Insect Pests of Economic Importance on Cereal Crops in the Senegal River Basin, West Africa

AN ABSTRACT- OF THE THESIS OF

Adama Sy for the degree ofMaster of Science

in Entomology presented on June 10, 1977

Title: INSECT PESTS OF ECONOMIC IMPORTANCE ON CEREAL CROPS

IN THE SENEGAL RIVER BASIN, WEST AFRICA Redacted for Privacy_ Abstract approved R. E. Berrybnd J. P. iattin

Cereal crops cultivated in Mali, Mauritania and Senegal consist primarily of sorghum, millet, rice and maize. They form the gramineous crops that, are programmed for the agricultural improvementof the Senegal River Basin. Twelve economically important insect pests on these crops were selected for study and treated with regard to their potential hazard to crop production. The selection of these insect pests was based on entomological investigations carried out in Senegal, Mali and the Senegal River Valley. Information was gathered from similar ecological areas in the Paleotropic region.

The following insect pests were selected: Diptera: Atherigona spp

(Muscidae), Contarinia sorghicola (Coquillet) (Cecidomyiidae) and

Orseolia oryzae (Wood-Mason) (Cecidomyiidae); Lepidoptera: Acigona ignefusalis (Hampson), Chilo zacconius Bleszynski, Maliarpha separatella Ragonot (Pyralidae), Heliothis armigera (Hubner), Sesamia calamistis Hampson, Spodoptera exempta (Walker) and Spodoptera littoralis (Boisduval) (Noctuidae); and Orthoptera: Locusta migratoria migratorioides (Reiche and Fairmaire) and Schistocerca americana gregaria (Forskal) (Acrididae). Information pertaining to the identification, distribution, host-plants, biology and control strategies, including agronomical and mechanical controls, varietal resistance, biological control and chemical control are presented for each pest.

The physical environment in the Senegal River Basin and agricultural production of the Senegal River Valley are described. An overall assessment of the pest complex of cereal crops is given and the present status of insect pest control in the Senegal River Basin is discussed. Insect Pests of Economic Importance on Cereal Crops in the Senegal River Basin, West Africa

Adama Sy

A THESIS

submitted to

Oregon State University

in partial fulfillment of the requirements for the degree of

Master of Science

Completed June 10, 1977

Commencement June 1978 APPROVED:

Redacted for Privacy

Professor of Entomology in charge of major

Redacted for Privacy

Head of Department of Entomology

Redacted for Privacy

Dean of Graduate School

Date thesis is presented June 10, 1977

Typed by Kitty Dougherty for Adama Sy ACKNOWLEDGEMENTS

My gratitude to Dr. R. Berry and Dr. J. Lattin is far greater than is possible to express. I have benefited from their kindness, support and understanding since my arrival in January, 1973 at Oregon State

University. Dr. R. Berry directed my academic training during my undergraduate work and he teamed with Dr. J. Lattin to organize my graduate program. Dr. J. Lattin recognized the need for entomological investigations in areas seldomly known for their entomofauna so as to anticipate entomological problems, and Dr. R. Berry foresaw the necess- ity of a compendium on the economically important insect pests of these areas so as to avoid entomological crisis. They provided the challenge and incentive with which I undertook this project. I am also thankful to Dr. W. Kronstad and Dr. T. Jackson for their valuable suggestions and their kind advice during the preparation of this project.

I would also like to extend my grateful acknowledgements to Gretchen

Dihoff, Scientific Librarian of the MUSAT: sra Project, University of

California, Riverside, and to her assistants for providing free access to the Sahelian literature. My sincere appreciation is also extended to

Dr. J. Breniere, Chairman of the Entomology Department of IRAT, Mont- pellier, France; J. Appert, Entomologist at the ORSTOM Centre de Dakar,

Senegal; B. Vercambre, Entomologist at the Institut Senegalais de

Recherches Agricoles, Bambey, Senegal; Galledou Tahara at the OCLALAV

Centre d'Aouin El Atrouss, Mauritania; Kane Hadya and Kane Cire at the

Ministry of Rural Development, Nouackchott, Mauritania, and to the Documentation Service of the Organisation pour la Mise en Valeur du

Fleuve Senegal (OMVS), St. Louis, Senegal, for the materials and suggestions they kindly provided. I am also indebt to Kitty Dougherty whose kindness and understanding supported the burden of typing this manuscript, and to literally hundreds of authors from whose work I have drawn freely the information presented. TABLE OF CONTENTS

Page

INTRODUCTION 1

Objectives 3

AGRICULTURE AND ECOLOGY OF THE SENEGAL RIVER BASIN 4

The Senegal River Basin 4

Location 4

Climate 6

Vegetation 8

Soils 10

Agriculture Production 12

Major crops 12

Potential crops 13

Crops and cropping systems 14

Management practices 15

INSECTS OF ECONOMIC IMPORTANCE ON CEREAL CROPS 21

Identity and Distribution of Major Groups of Pests 21

Crop Losses and Current Pest Control 23

Monographs of Selected Important Insect Pests 27

Diptera 27

Atherigona spp. [Sorghum shoot fly] 27

Identification 28

Distribution 29

Hosts 29

Damage 30 Page

Biology 31

Control strategies 35

Agronomical and mechanical control 36

Varietal resistance 36

Biological control 39

Chemical control 39

Contarinia sorghicola (Coquillet) [Sorghum midge] 41

Identification 42

Distribution 44

Hosts 45

Damage 45

Biology 47

Control strategies 51

Agronomical and mechanical control 52

Varietal resistance 53

Biological control 54

Chemical control 55

Orseolia oryzae (Wood-Mason) [Rice gall midge] 57

Identification 58

Distribution 59

Hosts 60

Damage 61

Biology 63

Control strategies 66 Page

Agronomical and mechanical control 68

Varietal resistance 68

Biological control 70

Chemical control 70

Lepidoptera 72

Acigona ignefusalis (Hampson) 72

Identification 73

Distribution 74

Hosts 75

Damage 75

Biology 76

Control strategies 79

Agronomical and mechanical control 80

Varietal resistance 81

Biological control 81

Chemical control 82

Chilo zacconius Bleszynski 83

Identification 84

Distribution 85

Hosts 85

Damage 86

Biology 87

Control strategies 90

Agronomical and mechanical control 90 Page

Varietal resistance 91

Biological control 92

Chemical control 93

Heliothis armigera (HUbner) [Old world boll worm] 95

Identification 97

Distribution 99

Hosts 100

Damage 100

Biology 102

Control strategies 105

Agronomical and mechanical control 106

Varietal resistance 107

Biological control 107

Chemical control 108

Maliarpha separatella Ragonot [Madagascar white rice borer] 110

Identification 111

Distribution 112

Hosts 112

Damage 113

Biology 114

Control strategies 115

Agronomical and mechanical control 117

Varietal resistance 117

Biological control 118 Page

Chemical control 118

Sesamia calamistis Hampson [Pink borer] 120

Identification 121

Distribution 122

Hosts 123

Damage 123

Biology 124

Control strategies 127

Agronomical and mechanical control 128

Varietal resistance 128

Biological control 129

Chemical control 130

Spodoptera exempta (Walker) [African Army worm] 131

Identification 131

Distribution 134

Hosts 134

Damage 135

Biology 136

Control strategies 138

Agronomical and mechanical control 140

Varietal resistance 140

Biological control 141

Chemical control 142

Spodoptera littoralis (Boisduval) [Egyptian Cotton worm] 144 Page

Identification 145

Distribution 147

Hosts 148

Damage 149

Biology 150

Control strategies 153

Agronomical and mechanical control 154

Varietal resistance 155

Biological control 156

Chemical control 156

Orthoptera 158

Locusta migratoria migratorioides (Reiche and Fair- maire) [African migratory locust] 158

Identification 160

Distribution 163

Hosts 165

Damage 167

Biology 170

Control strategies 174

Schistocerca americana gregaria (Forskal) [Desert locust] 176

Identification 178

Distribution 182

Hosts 183

Damage 184 Page

Biology 189

Control strategies 193

Agronomical and mechanical control 196

Varietal resistance 197

Biological control 198

Chemical control 200

CONCLUSIONS 202

BIBLIOGRAPHY 204 LIST OF TABLES

Table Page

I. Area, Production and Yield of Sorghum and Millet in the Senegal River Valley 17

II. Area, Production and Yield of Rice in the Senegal River Valley 18

III. Area, Production and Yield of Maize in the Senegal River Valley 19

IV. Area and Production of Major Cereal Crops in Senegal, Mali and Mauritania 20 INSECT PESTS OF ECONOMIC IMPORTANCE ON CEREAL CROPS IN THE SENEGAL RIVER BASIN, WEST AFRICA

INTRODUCTION

The Senegal River Basin is composed of areas distributed in the

four West African states of Guinea, Mali, Mauritania and Senegal.

Mali, Mauritania and Senegal contain the largest portion of the river

basin, including the Senegal River Valley, which is the principal area

for crop production. With the exception of Guinea, the states form

the western section of the Sahelian zonel, whose fragile ecosystems

and vulnerable environments underline the precarious living conditions

found there (see MAB technical notes 1975, and Anonymous 1975a).

One way to meet the challenge which is imposed by the physical

environment is the pooling together of commonly held natural resources.

This has been recognized by the Sahelian countries who have set up an

agency to formulate regional programs (Comite Inter-etats de lutte

contre la secheresse au Sahel-CILSS)2 (Anonymous 1975a). The states of

Mali, Mauritania and Senegal have also formed the Organization for De-

velopment of the Senegal River (Organisation pour la Mise en Valeur du

3 Fleuve Senegal-OMVS) , whose objectives, among others, are to regulate

crop production in the Senegal River Valley.

1The Sahelian zone extends between the Sahara desert in the north and the Sudanic zone to the south, and as a fringe, it spreads along the desert from the Atlantic ocean to Ethiopia, Somali and Kenya (Berry 1975). 2Included in the Agency are the states of Chad, Gambia, Mali, Mauri- tania, Niger, Senegal and Upper Volta (Anonymous 1975a). 3The old organization did include Guinea and was called: Organisa- tion des Etats Riverains du Senegal-OERS (Nelson et al. 1974). 2

Reorganizing the crop production design of the Senegal River Valley calls for regulating the Senegal River's dynamics and the introduction of improved farming methods (e.g. irrigation, double cropping and high yielding varieties), consequently, this would remodel the ecological background of the biota. But, as Gilbert White (1972) wrote, "a puzzl- ing aspect of many development projects is why they are not accompanied by more searching scientific investigations of their ecological consequences..." (Cited after Dasmann et al. 1974, p.183). Uvarov

(1960, 1961) pointed out that in planning any development of arid lands for agriculture, grazing or forestry, it is essential to take into account insect pests as a major hazard.

Although losses due to insect pests are poorly known in crops grown in the Senegal River Valley, Sasser et al. (1972, p.10) have found in

several African states, including Senegal and Mali, that "virtually all crops are faced with a complex of serious pest problems and losses on crops are high, certainly beyond tolerable levels", and Cramer

(1967, p.145) stated that "to put losses due to insect pests at 10%

from the potential production [millet, sorghum] is an extremely cautious

estimate". Insect pest problems have been intensified with changes

from traditional to modern farming (Nickel 1973), and more often, the

plasticity of the pest was the direct reflection of the ecological

design (Rivnay 1964, Dasmann et al. 1974). Thus, the insect component

could, by itself, reduce or prevent the objectives of the agricultural design from being achieved. This adds a new dimension to the global

strategy where planning for better viability of the present and future

cropping systems is anticipated. 3

Objectives

The objectives of this study were to gather the already available but widely scattered information of the economically important insect pests of cereal crops grown or intended to be grown in the Senegal

River Basin. This study provides materials for the planner for more adequately assessing and anticipating the type of information and management needed to minimize adverse effects of the insect pests.

It also provides materials which can be used in extension service, in organizing research, in the School of Agriculture, and as a reference and directory on important insect pests to be used by plant pro-

tection services. 4

AGRICULTURE AND ECOLOGY OF THE SENEGAL RIVER BASIN

According to Martine (1948), interest in developing agriculture

in the Senegal River Valley began in 1820, when Richard established

the first plant nursery in the Senegalese town known since as Richard

Toll. In the late 1930's, the organization known as Mission d'amen-

agement du Fleuve Senegal (MAS) created additional agricultural ex-

periment stations along the Senegal River (e.g. Diorbivol, Guede), and

began studying the Senegal River dynamics. Appert (1952) did the first

entomological survey in the Richard Toll-Matam segment of the valley.

Since that time, various studies have been made on the dynamics of

the Senegal River and the physiognomy of its basin. These studies

have assessed the potential of crop production in the area. Several

. of these studies are in unpublished documents and the following ac-

counts are mostly taken from Beyrard (1974a,b,c), Nelson et al. (1974)

and Curran and Schrock (1972).

The Senegal River Basin

Location:

The Senegal River Basin lies between 10°20' and 17°30' North lat-

itude and between 7° and 10°30' West longitude. The area covers

335,000 square kilometers and is divided into 32,000 km2 in Guinea,

102,000 km2 in Mali, 126,000 km2 in Mauritania and 75,000 km2 in Sene-

gal (Felix-Brigaud 1961). The basin incorporates the drainage areas

of the Senegal River and the river's affluents and tributaries, of

which Bafing, Bakoye, Faleme, Baoule and Gorgol are the most important. 5

The Senegal River proper is made up of the Bafing and the Bakoye which unite at Bafoulabe in Mali, and thereafter, form a single

stream, although, the Bafing is generally considered the upper stream of the river (Chaumney 1973). The River stretches over 1800 km in

length, from its head waters in the Massif of Fouta Djallon in Guinea,

to its mouth at Saint-Louis in Senegal, where it also drains into the

Atlantic ocean. In doing so, the river cuts across Western Mali and

forms the International boundary between Senegal and Mauritania.

The River cuts across a wet and dry zone along its path from the

Massif of Fouta Djallon to the Atlantic ocean. The wet zone corre-

sponds to the Guinean and Sudanian zones and provides the flood water which is carried into the Sahelian or dry zones. The Upper Basin lies

in the wet zone and incorporates the area from the Massif of Fouta

Djallon to Bakel in Senegal and constitutes 70% of the Basin

(Beyrard 1974a). The Lower Basin includes the Sahelian zone and in-

corporates the area from Bakel to the Atlantic ocean. This last segment includes the Senegal River Valley (Bakel to Dagana) which com-

prises ten to 25 km wide flood plains and the Delta (Dagana to the

Atlantic ocean), which forms a large area watered by various channels

of the River from downstream near Dagana.

According to Chaumney (1973) the River annually floods 200,000

hectares of land in the Lower Basin, 100,000 to 130,000 hectares of which are farmed. Felix-Brigaud (1961) stated that 200,000, 500,000

and 800,000 hectares would be flooded annually by the River, depend-

ing on years of low, moderate or high flood heights, respectively. 6

The Senegal River Valley and the Delta form the major crop producing areas of the Basin and provide 75-80% of the cereal cropproduction of Mauritania and approximately 8% of millet and sorghum, 20% of rice and 22% of maize production in Senegal (Beyrard 1974b). In addition, the areas form the trunk of the intended crop production schemes (Chaumney 1973, Beyrard 1974a).

Climate:

The annual average rainfall of the Upper Basin is said to de-

crease from 2000 mm in the southernmost segment (Guinea) to 700 mm in

the northernmost segment (Bakel). The Lower Basin falls in the semi-

arid to arid segments and its average rainfall is less than 500mm

(200-500 mm).

The wet zone (Upper Basin) corresponds to the Sudanian zone, which,

according to Jaeger (1968) is characterized by dry and rainy seasons.

The dry season lasts four to seven months, depending on location, and

includes a cold and dry period. The cold period lasts from December to

January with minimum daily temperatures reaching 11°C. The dry period

lasts from March to May and daily temperatures reach 40-45°C. The

trade wind Harmattan blows during this period and maintains continuously

high temperatures. The rainy season is generally cooler and peaks of

rainfall occur in August.

The semi-arid to arid segment (Lower Basin) corresponds to the

Sahelian zone, although the northernmost segment dips into the much

drier Sahelo-Saharian zone. According to Berry (1975), rainfall is

the crucial element of the climate in the Sahelian zone. Continuous

and complex climatic fluctuations have existed in Sahelian areas 7 during the Pliocene and Recent. The overall result of these fluctuations is the vulnerable environment of the Sahel. According to the

Institut de Recherche Agronomiques Tropicales et des cultures vivieres

(I.R.A.T.), 1972, the people of the Senegal River Valley (Kaedi) generally recognize five seasons, as follows:(1) The NDOUGOU or rainy season, which lasts from June to September with a relative humidity of

60-90% and temperatures above 30°C.;(2) the KAOULE (October to Novem- ber);(3) the DABOUNDE or cold and dry season which lasts from December to February, with temperatures as low as 10°C. but with daily thermal amplitude reaching 20°C. This period is also the onset of the trade wind Harmattan which is reported to lengthen the vegetative cycle of subsiding sorghum (I.R.A.T. 1973a);(4) the THIEDOU which corresponds to the dry season proper and lasts from March to April with temperatures exceeding 40°C., and (5) the DEMINARE or last period, corresponding to a transitional period before the rainy season.

The common feature of climate in the Basin is said to involve the variation of rainfall, particularly in the Lower Basin, and the dynamics of the River, primarily its flooding heights. Beyrard (1974a) found that ± 10 to 30% variation on the "normal" average annual rainfall was common in the Lower Basin and generally, years of below normal average rainfall were more frequent than years of above normal average rainfall. He concluded that the cycle corresponds to normal, humid, very humid, dry and very dry years. I.R.A.T. (1972) also found that for a period of ten years, the amount of rainfall considered 8 normal at Kaedi (average of 400 mm/year), was below the normal average for six years, and normal or above normal average for only four years.

The River floods from June to November, corresponding to the rainy season. During this season, the River exceeds its banks and in- undates the vast plains of the Valley and the Delta. The inundation period, velocity and discharges of the River are variable within the areas. According to Felix-Brigaud (1961), flooding starts in mid-

June at Bakel. The flood heights are variable, and on the average, the rise above low water is about 45 feet at Bakel and decreases to approximately 12 feet at Dagana. During the dry season (November to

May), the water level of the River is low and the water flows only in the River's minor bed, which is dry in some areas.

Vegetation:

The flora of Mali was reported by Jaeger (1968), Adam (1968a,b) gave an account on the flora of Senegal and Mauritania, and Schnell

(1968) treated the flora of Guinea. In each area, the floristic composition and distribution reflects climatic zones which are affected by the rainfall. Rainfall also influences the flora of the Senegal

River Basin, with the exception of the flood plains, where the flood heights influence the physiognomy of the vegetation.

According to Perraudin (1972) (in Beyrard 19742), vegetation in the Upper Basin forms a woodland savanna and a parkland forest. The floristic composition changes along the gradient South-North, depending on topography and rainfall. He stated that gramineous plants such as Pennisetum purpureum and Andropogon gayanus are the major 9

species of the herbaceous stratum, while among the trees, species

such as Combretum glutinosum (Combretaceae) are commonly found. He

described the vegetation of the Sahelian zone in the Lower Basin as

forming a wooded steppe of low trees and shrubs. Acacia raddiana

and Acacia flava (Mimosaceae) and Balanites aegyptiaca (Simarubaceae)

form the major tree species, while Shoenefeldia gracilis and Latipes

senegalensis (Graminae) and Borreria radiata (Rubiaceae) are the

dominant species in the herbaceous layer. He also reported that

savanna of Andropogon gayanus and Hyparrhenia dissoluta (Graminae)

may form in sandy places, and forests of Acacia nilotica (Mimosaceae)

are found on the flood plains.

SEDAGRI (1973) (in Beyrard 1974a) distinguished different phyto-

sociological groups in the Lower Basin. Acacia nilotica is found on

pool and flooded lands, Bergia suffriticosa (Elatinaceae) and Indigofera

oblongiflora (Papilionaceae) are found on occasionally flooded lands;

species of Acacia (Mimosaceae), Balanites (Simarubaceae), Bauhinia

(Caesalpiniaceae), Ziziphus (Rhamnaceae) and Capparis (Capparidaceae) are

found on seldomly flooded lands, and Acacia raddiana (Mimosaceae) and

Tamarindus indica (Caesalpiniaceae) are the major species on land never

flooded. According to Adam (1968a), the common aquatic graminae are:

Echinochloa stagnina, Oryza barthii, Echinochloa pyramidilis, Vossia

cuspidata, Polygonum senegalense and Diplachne fusca. Different groups

of vegetation are found in the saline soils of the Delta and correspond to groups of Arthrocnemum glaucum (Chenopodiaceae), Paspalum vaginatum (Graminae) and Sporobolus robustus (Graminae), respectively 10

(SEDAGRI 1973 in Beyrard 1974a).

Soils:

Michell (1969) discussed the geomorphology and pedogenesis of

the Senegal River Basin and SEDAGRI (1973) (in Beyrard 1974a) surveyed the soils of the Senegal River Valley. Durand (1965) studied the soils of the Boghe Flood plains (Mauritania) and Sys (1969) reviewed the classification of African soils and attempted to make a correlation with the U.S. soil classification system (7th approximation).

Agricultural soils of the Senegal River Valley are divided into soils of the flood plains and river banks and soils outside the flood plains. The division also corresponds to two cropping zones in the

Valley (see crops and cropping systems). The flood plains are known as OUALO and the outside flood plains as DIERI. They correspond to different soil-types which are traditionally classified according to their levees, flood potential, material and color, and agronomic suitability (Durand 1965). Chaumney (1973) and SEDAGRI (in Beyrard 1974a) adopted the indigenous system schemes of classification and divided the soils of the flood plains into Fonde, Hollalde and Faux Hollade, which correspond to soils of less than 30%, more than 50% and 30-50% clay content, respectively. According to Michell (1969), the Fonde corresponds to soils developing on high levees of fine sand and silt bordering the present path of the River and also its dead arms and tributaries. They also represent soils with ferromanganese concre- tions and their flooding period varies from 0-30 days. The Hollalde corresponds to soils forming on clayey ground depressions which are 11 flooded from 30-120 days and represent "topomorphic vertisols". In addition, Michell (1969) recognized the following soils: soils forming on pools where the duration of the flood exceeds 150 days and where water may stagnate throughout the dry season (Vindou), soils of fluva- tile origin where alluviation is still continuing (Djedjagol), soils of the present River banks which develop from sandy deposit (Falo), and soils of erroded old banks which develop on clayey sand and present large ochre-rust patches of iron sesquioxide accumulation (Diacre).

The DIERI corresponds to the floodless lands situated above the flood plains (Durand 1965). It represents coarse-textured and reddish- brown soils which are characterized by a high hydraulic conductivity and high base saturation (mostly calcium) (Durand 1965). These soils are formed on sand dunes derived from the Ogolian (dry period which occurred 15,000 to 20,000 years ago, Michell 1969) and they are classified as Psamustent (Entisol) (Durand 1965).

According to Martine (1948) the Fonde and the Hollalde soils are low in organic matter content. SEDAGRI (1973) (in Beyrard 1974a) found that soils of the flood plains are deficient in phosphorous, sulfur, and in some areas, magnesium. Chaumney (1973) stated that these soils are also deficient in nitrogen and they respond to fertilizer applications. He further added that 75% of soils of the Delta are halomorphic soils. 12

Agriculture Production

Major crops:

Food crops of Mali, Mauritania and Senegal are: millet, sorghum, rice, maize, niebe (Vigna unguiculata), cassava (Manihot utilissima) and sweet potato (Ipomea batatas). Wheat is grown in small areas in

Mauritania and Fonio (Digitaria spp) is cultivated in the wet zones of

Senegal and Mali. Millet and sorghum form the dominant food crops and are grown extensively in large areas in each country. These two cereal crops occupy 70-80% of the cultivated lands and account for 55% of the total food crop production in Senegal (International Bank for Recon- struction and Development: I.B.R.D. 1974), 62.2% of the farmed lands in Mali (Direction Statistique Mali: Dir. Sta. Mali 1975), and provide

60-65% of the total crop production in Mauritania (Beyrard 1974b.)

Rice is the second significant food crop and is widely grown in parts of

Senegal (Casamance) and Mali (Niger flood plains), while in Mauritania, rice has recently been introduced and is mainly grown in the Senegal

River Valley. Maize is an important diet component of these states, although, the crop is widely cultivated only in Mali (Bono 1970) and parts of Senegal (Sene 1966). Mango (Mangifera indica) is the main crop among fruit crops of Senegal and Mali, while date palm (Phoenix dactylifera) covers extensive areas (Oasis) in Mauritania (Beyrard 1974b). Indus-

trial crops such as groundnut (Arachis hypogea) and cotton are major ex- ports in Senegal and Mali, and sugar cane (Saccharum officinarum) has been expanded in Mali and Senegal, and forms a major component of the

Gorgol Valley (Mauritania) cropping system. Vegetable crops are produced in sufficient quantity in Mali and Senegal, but are grown only in small 13 areas in Mauritania (Beyrard 1974b).

The above crops form the crop production system of the Senegal

River Valley, but the area is more specialized in gramineous crops, of which sorghum and millet are of overriding importance (Sene 1966).

In addition, the area has the potential of ending the chronic cereal grain shortage of Senegal and Mauritania, providing adequate irrigation is achieved.

Rice is the major crop presently grown under irrigation and various agencies have been established in Senegal (I.B.R.D. 1974) and in Mauri- tania (Anonymous 1975d) for managing rice projects in the Senegal River

Valley. The areas, yield and production of the major cereal crops which are grown in the Senegal River Valley are given in Tables I, II, and III. The areas and overall cereal crop production of Senegal, Mali, and Mauritania are given in Table IV.

Potential crops:

Emphasis on producing enough cereal grains has been among the major agricultural policies of Senegal (Direction Agriculture, Senegal: Direc.

Agri. Senegal, 1963), Mali (Bouchet 1963) and Mauritania (I.B.R.D. 1968,

Anonymous 1975d), and also of the Regional Organization (OMVS) which

incorporates these states (Beyrard 1974b). The cereal crops receiving

the major emphasis in these polices are, sorghum, millet, rice and maize.

Other crops involved in the programs are, wheat, pastures and cotton

(primarily in Mauritania) and leguminous crops, such as niebe

(Vigna unguiculata), sugar cane, vegetables and fruit trees. 14

Crops and cropping systems:

According to Sene (1966), millet and sorghum which are grown in

Senegal, are comprised of two and three main groups, respectively.

Millet (Pennisetum spp) is divided into the Souna-types, which are

early maturing varieties (90-100 days) and the Sanio-types, which are late maturing varieties (150 days). The sorghum group includes the

Caffras which are grown on receeding flood plains, and Guinnensis and

Durra, which are the rain-fed sorghums. Among the rain-fed sorghums, the Guinnensis are the most widely cultivated and include several varieties, whose length of growing periods would classify them into short or late maturing varieties. The Durra groups are essentially made up of late maturing varieties. The cultivated maize varieties are short-cycle varieties (70-100 days) (Sene 1966, Bono 1970). The rice groups include Oryza sativa on irrigated lands and Oryza glaberrima (African rice) on swamps or upland cultivations.

Two cropping periods are usually recognized with the exception of irrigated rice. These periods correspond to what is locally termed in the Senegal River Valley as 1) farming the DIERI and 2) farming the

OUALO (Sene 1966, Anonymous 1967). Early maturing varieties of millet and sorghum are farmed during the rainy season in the DIERI and their growth depends entirely on rainfall. They occur either as pure stands, or more often, in mixed cropping with niebe (Vigna unguiculata) and occasionally with beref (Citrullus vulgaris). Sorghum and maize are the major crops which are grown during the dry season in the OUALO and correspond to the subsiding crops of the flood plains. The OUALO 15

is formed of clayey soils (see soils) and is generally able to retain enough moisture to allow the growth of sorghum and maize. Additional farming is done during the dry season on the exposed River banks, lakes and ponds, and usually involves maize and vegetable crops. With the exception of the Fonde (see soils), all the recognized soils

(Hollalde and Faux Hollalde) have the potential for rice cropping.

Management practices:

Bourke (1963) discussed the traditional farming practices of millet in West Africa, and Sene (1966) and Direc. Agri. Senegal (1963) described farming practices for sorghum and millet in Senegal. Tra- ditional farming involves several simple practices borne from the farmer's experience with his crops and the environment of his cropping; it is generally considered as "a production system operating at a lowenergy level and approaching a state of biological equilibrium"

(Schultz 1964, in Smith 1974, p.3). Traditional farming practices

in the Senegal River Valley involve sowing in the DIERI after the first significant rain following the dry season, and planting in the

OUALO as soon as floods have receeded. Thereafter, the practices consist of weeding the fields, which takes the bulk of the labor in DIERI and protecting the crops, particularly in OUALO (e.g. from Weaver bird: Quelea spp) since it forms the only green area during the dry

season. The process ends with crop harvesting which varies in DIERI and OUALO. The time of farming depends on flood retreat in the latter and rainfall in the former. The OUALO and the DIERI systems are both labor demanding, although they require different amounts of energy 16 expenditure.

The farm size averages 3.77 ha of DIERI '+ OUALO for a farming family unit of 5.7 individuals (MISOES in Beyrard 1974a). The yield averages 250-400 kg/ha of millet in DIERI and 450 kg/ha of sorghum in OUALO. Fertilizers and pesticides are not used extensively, although various experiments have shown their significance in im- proving yield. For instance, Sene (1966) reported that 300 kg/ha of ammonium sulfate in a split application increased millet yield from

300 to 1,416 kg/ha, and 3,000 kg/ha of maize were obtained by application of 530 kg/ha of a combination of ammonium sulfate, bicalcic phosphate and potassium chloride. I.R.A.T. (1973a) reported that sorghum grown on flood plains can yield 1500-2000 kg/ha, provided it is sown immediately and given 100 units of nitrates/ha. Bouchet

(1963) reported that seed dressing with 20 g/ha of technical Thiram

(fungicide) increased sorghum yield by 30%. However, according to

Deuse (1972), the annual use of pesticides in Senegal is no more than one kg/ha per year, and I.B.R.D. (1974) found that the use of fertilizers have substantially decreased in Senegal. Table I. Area, Production and Yield of Sorghum and Millet

in the Senegal River Valleya

1961/621962/631963/641964/651965/661966/671967/681968/691969/701970/71 Senegal

Area (hectares) 121,000126,601123,660141,000140,685141,786159,681123,542130,318109,440

Production 59,190 63,049 47,667 80,500 66,150 65,045 87,313 43,054 83,914 31,558 (metric tons)

Yield (kg/ha) 490 498 385 570 470 460 547 348 644 288

Mali

Area 73,335104,865109,852 99,391

Production 149,600141,000141,000189,000135,800 89,120102,905115,800117,915

Yield 210 980 1,054 1,186

Mauritania

Area 156,000158,000160,000160,000178,000160,000178,000 89,000178,000160,000

Production 70,000 71,000 72,000 72,000 80,000 72,000 90,000 40,000 90,000 72,000

Yield 450 450 450 450 450 450 450 450 450 450

aThe data corresponds to areas, production and yield of crops of each segment of the Senegal River Valley located in Mauritania, Senegal and Mali. (Modified after Rodts 1972) Table II. Area, Production and Yield of Rice

in the Senegal River Valleya

1961/621962/631963/641964/651965/661966/671967/681968/691969/701970/71 Senegal

Area (hectares) 7,630 7,960 8,350 9,190 12,520 15,560 16,115 6,413 16,470 10,030

Production (metric tons) 17,620 19,540 23,090 21,975 27,515 38,195 28,180 11,945 30,095 20,100

Yield (kg/ha) 2,300 2,450 2,765 2,390 2,198 2,453 1,740 1,860 1,830 2,000

Mali

Area 3,850 8,560 3,910 3,820

Production 5,600 7,800 2,900 4,100

Yield 1,260 825 642 1,033

Mauritania

Area 300 250 500 500

Production 600 500 1,000 1,250

Yield 2,000 2,000 2,000 2,500

in the Senegal River Valleya

1961/621962/631963/641964/651965/661966/671967/681968/691969/701970/71 Senegal

Area (hectares) 9,550 9,865 8,405 19,700 22,000 24,038 21,173 8,615 17,960 16,217

Production (metric tons) 7,510 6,214 4,946 12,496 12,600 15,496 23,562 4,686 13,580 14,290

Yield (kg/ha) 786 630 590 635 573 645 1,112 756 880

Mali

Area 12,328 10,980 10,270 12,040

Production 14,970 11,671 9,600 15,040

Yield 976 950 730 1,110

Mauritania

Area 6,500

Production 3,000 3,700 6,000 3,800 4,000 3,000 3,000 4,000

Yield

in Senegal, Mali and Mauritaniaa

Area harvested(x1000 ha) Production(x 1000 tons)

1961-65 1972 1973 1974 1961-65 1972 1973 1974

Rice Paddy

Senegal 76 54 65 68 100 37 64 95 b b Mali 175 184 135 180F 170 195 100 200F

b b b b Mauritania 1F 1F 1F 1 1F

Maize

Senegal 39 32 36 31 32 20 31 40

b b Mali 74 9OF 90 90 80 6OF 80 87 b b b b b b b Mauritania 6F 7F 6F 6F 4 4F 3F 3F

Sorghum + Millet b b Senegal 956 936 947 1000F 483 323 486 500F b b b b Mali 1132 1200F 1200F 1250F 782 600F 525 600 b b b b b b Mauritania 254 220F 160F 160F 93 5OF 3OF 3OF

aSource: Production Yearbook, F.A.O. 1974, vol. 28,1 b= F.A.O. estimates ON.) 21

INSECTS OF ECONOMIC IMPORTANCE ON CEREAL CROPS

Identity and Distribution of Major Groups of Pests

Risbec (1950) and Appert (1957) have identified the economic

entomofauna of the cultivated crops of Senegal and Mali. Appert

(1963) and Breniere (1967) surveyed the pest complex of gramineous

crops of Senegal and provided a partial listing of the major and

potential pests. Breniere (1969, 1970, 1971), Buyckx (1962),

Bouriquet (1963), Appert (1964, 1971a) and Risbec and Mallamaire

(1949) described the insect pests of francophone West Africa, and

York (1967, 1970), Nye (1960), Schmutterer (1969) and Rivnay (1962)

listed the major insect pests of crops of West Africa, East Africa,

Sudan and East Central Africa and Mediterranean Africa, respectively.

Cotterell (1963) and Caresche et al. (1969) provided a synopsis on

the major insect pests of Continental Africa and a multidisciplinary pest management team identified the economically important insect

pests of several African states, including Senegal and Mali

(Sasser et al. 1972).

Many of the above authors concluded that the economically impor-

tant insect pests of cereal crops could be classified broadly into

stem borers (Lepidoptera: Pyralidae and Noctuidae), shoot borers

(Diptera: Muscidae and Diopsidae), earhead pests (Lepidoptera:

Noctuidae and Diptera: Cecidomyiidae) and grasshoppers and locusts

(Orthoptera: Acrididae) (U.S.A.I.D. 1974, Breniere 1970, Sasser et al.

1972). However, the insect complex varies with geographical location 22 and its economic status depends on the level of agriculture practiced

(traditional versus ameliorated). The second major group of insect pests of gramineous crops includes sporadic lepidopterous pests. e.g. Spodoptera spp (Noctuidae) which are commonly ranked as secondary pests (Young and Teetes 1977, Young 1970). Hemipterous groups also cause significant damage to rice crops (Grist and Lever 1969) and species of Nezara (Pentatomidae), and Dysdercus (Pyrrhocoridae) have been found to greatly reduce yield of sorghum (Bowden 1965). The corn leaf aphid Rhopalosiphum maidis (Fitch) and the sorghum aphid

Melanaphis sacchari (Zehntner) (Homoptera: Aphididae) are listed among the potential insect pests of sorghum and maize (Young 1970).

The species are vectors of millet red leaf-virus (Kennedy, Day and

Eastop 1962), and the corn leaf aphid is a vector of sugar cane mosaic virus. According to Mallamaire (1954), the sorghum aphid is a well known pest of subsiding sorghum in the Senegal River Valley. Among coleopterous pests of sorghum and millet, Lema spp (Chrysomelidae) are said to cause severe damage on young seedlings (C. Agr. Pr. Pays

Chauds 1965).

Bioclimatic zones and geographical areas have not been defined for any particular group of insect pests of cereal crops that were identified in either Senegal or Mali. Rather, the groups appear to be widely distributed in these countries and are similar to those found in other Sahelian areas (Sasser et al. 1972). Appert (1952) listed the major groups of insect pests found in the Senegal River Valley and he concluded that the important species corresponded to widely known 23 species in Africa. Schmitz (1969) also listed the economically important insect pests of crops of the Senegal River Valley. The pests were found to correspond broadly to those found in other areas of

Senegal and Mali. Schmitz's list (1969) included: Chilo zacconius

Bleszynski (Pyralidae), Maliarpha separatella Ragonot (Pyralidae),

Eldana saccharina (Walker (Pyralidae), Acigona ignefusalis (Hampson)

(Pyralidae), Sesamia cretica Lederer, and Sesamia spp (Noctuidae) which are all lepidopterous stem borers. Eublemma gayneri Roth

(Noctuidae), Pyroderces hemizopa Meyer (Cosmopterigidae), Contarinia sorghicola (Coquillet) (Cecidomyiidae), and Geromyia penneseti (Felt)

(Cecidomyiidae) are the earhead pests and a last group including:

Heliothis spp (Noctuidae), Cirphis loreyi (Duponchel) (Noctuidae) and

Spodoptera spp (Noctuidae) are cosmopolitan Lepidoptera.

Crop Losses and Current Pest Control

There is poor knowledge of losses due to insects in many of the cereal crops. However, Sasser et al. (1972) found that for several

African states, the losses are usually high, and Smith (1974, p.4) stated that traditional agriculture is beset with a wide range of pest problems. In Senegal, it is said that cecidomyiid pests and lepidopterous stem borers cause significant losses to cereal crops.

LecLerq (1962) (in Cramer 1967) stated that Contarinia sorghicola

(Coquillet) caused 50% reduction in yield to sorghum not ripening at the same period. Coutin (1970) reported that 50-90% losses in sorghum were due to this species in 1967-1969, and another midge Geromyia 24

penneseti (Felt), caused 40% loss to late maturing millet (Schmitz

1969). The lepidopterous stem borer, Acigona ignefusalis (Hampson) damages rainfed millet in the Senegal River Valley (Schmitz 1969) and is a set back to late maturing millets in Eastern Senegal (Bren- eire and Coutin 1969). Schmitz (1969) found that subsiding sorghum was free of stem borer pests, but irrigated rice was heavily to moderately infested by Chilo zacconius Bleszynski and Maliarpha separatella

Ragonot, respectively. He concluded that the damage incidence of the pest complex was related to the season, cropping system (DIERI versus

OUALO) and cropping schemes (irrigated versus rainfed crops). Acridid

(Orthoptera) populations are common features of arid land (Uvarov 1957).

They are said to involve more than 40 species of grasshoppers, 15 of which are of major significance (U.S.A.I.D. 1974), as are four locust species, namely the desert locust Schistocerca americana gregaria (Fors- kal), the tree locust Anacridium melanorhodon (Walker), the African migratory locust, Locusta migratoria migratorioides (Reiche and Fair- maire) and the red locust, Nomadacris septemfasciata (Serville). While the potential damage of these pests is recognized in the Sudano-Sahelian zone (Sub-Saharan ecological zones stretching from Senegal to Ethiopia,

U.S.A.I.D. 1974, p.1), quantitative damage estimates are poorly document- ed. According to Kane (1977) (Personnel Communication), 50% and 25% of crops grown during the rainy season and on the flood plains in the dry season, respectively, were lost owing to grasshopper damage in Mauri-

tania in 1975-1976. According to Singh (1974) approximately 30 to

100% losses of millet and sorghum were observed during grasshopper 25 outbreaks in 1974 in many Sahelian countries.

Little insect pest control is practiced in traditional farming owing to several factors of which economics is perhaps the most important. According to Smith (1974), it is unwise to impose modern pest management practices on such systems without changing the basic production potential. However, several practices that the farmer uses

(e.g. early planting, mixed cropping, weeding) constitute indirect means of controlling the pests. On the other hand, shifting cultivation may induce floral and faunal diversity and may lead to small fluctuations of the pests (Nickel 1973) or provide suitable habitats, particularly in arid lands, to locust and grasshoppers (Uvarov 1957,

1964) and lead to pest outbreak.

Artificial input, such as pesticides, are not used extensively with the exception of partial seed dressing and subsided cash crops.

Sasser et al. (1972) found that only 5% of the millet and sorghum seeds were treated with insecticides in Mali. In Senegal, they found that small amounts of pesticides were used, mainly against the rice stem borers. These authors concluded (p.12) that "farmers producing at the subsistence level simply cannot afford insecticides, fertilizers, etc. at the present time (or in the foreseeable future) ". However, plant protection services have been established in Mali, Senegal and

Mauritania, and are broadly aimed at controlling vertebrate and invertebrate pests. Further, they provide expertise to farmers for insect pest controls. In addition, International organizations such as 26

O.I.C.M.A., (Organisation Internationale contre le criquet migrateur

Africain) and O.C.L.A.L.A.V.,(Organisation commune de lutte antiacridienne et antiaviaire) provide the basic control of such pests as locusts. 27

Monographs of Selected Important Insect Pests

Diptera

Atherigona spp

Common name: Sorghum shoot fly

Order: Diptera

Family: Muscidae

A large number of Diptera of the genus Atherigona Rondani are reported to attack cereal crops, particularly sorghum species. The general common name, sorghum shoot fly, may refer to different species of

Atherigona Rondani as observed by Deeming (1971), Baliddawa and Lyon

(1974) and Jotwani, Verma and Young (1969).

Risbec (1950) and Appert (1957, 1963) reported that A. quadripunctata Rossi is among the insect pests of cereal crops of Senegal. Bren- iere (1970) reported that the same species infests shoots and young seedlings of sorghum plants in the "French West African" countries.

The Institut Senegalais de Recherche Agricoles (I.S.R.A.) 1976, listed

A. quadripunctata as anonymous of A. ponti, a species described as new in Deeming (1971). Both East African and Asiatic literature on sorghum shoot fly deal essentially with A. varia soccata Rondani (review of

Young 1970, Young and Teetes 1977).

The above notes suggest that may species are involved and their taxonomical position is still not clearly defined, although Deeming

(1971) offered a thorough treatment of the subject. The review of

Young (1970) reported that the shoot fly (Atherigona varia soccata) 28 has generally been considered a minor or occasional pest in Africa and the Indian subcontinent. However, the fly is assuming a greater importance since the introduction of sorghum hybrids and intensive cultivation of sorghum crops. Breniere (1972) holds the view that

Atherigona species can be a potential threat, particularly to off-

season irrigated sorghum crops.

Identification:

According to Deeming (1971) the genus Atherigona comprises 145

species, five subspecies and one variety. From these, he listed 71 species and two subspecies as endemic to the Ethiopian region, including the Atlantic Islands. He provided keys to the species found

in the Ethiopian region and stated that the keys are only applicable to male adults.

Short descriptions of A. quadripunctata are found in Risbec (1950) and Appert (1963). Venturi (1940, 1968) in Deeming (1971) also described A. quadripunctata and summarized its life history.

The species A. quadripunctata in Senegal, was described by Risbec

(1950) and Appert (1963) as follows: the adult fly is small, about

3.5 mm in length. The abdomen is yellowish and bears black spots on the posterior sides. The wings are hyaline 'lanes transparentes, in- colores, finement pubescentes, bordees de soles" Risbec (1950, p.114).

The full grown larva is about 5-8 mm long, with black mouth parts.

The general color of the larva is cream. The pupa is elongated, reddish brown, "pope cylindrique, tronquee vers la tete, arrondie en arriere, marron rougeatre" Risbec (1950, p.114). The egg is white, convex on the upper sides and ribbed longitudinally, "L'oeuf est blanc, 29 convex a sa partie superieure, et strie longitudinalement" Appert

(1963, p.34).

Distribution:

Appert (1963) reported that A. quadripunctata is widely distributed in Africa. Both Risbec (1950) and Appert reported that the insect occurred in Senegal. Breniere (1970, 1972) listed the same species as being distributed in Sahelian regions, particularly with reference to former "French West Africa". Hennig (1961) in Deeming

(1971), listed A. varia soccata as widely distributed throughout the tropics and subtropics of the old world, from the Canary Islands to

Central Asia and from Northern Italy to Uganda.

Hosts:

Deeming (1971) compiled a list of the recorded hosts of A. varia soccata. The list included: cultivated sorghum, Sorghum vulgare,

Sorghum halepense, Sorghum verticilliflorum, Cynodon dactylon, Eleusine coracana, Pennisetum thyphoides, Panicum miliare, Panicum miliaceum,

Brachiaria brirantha, Desmostachya bipinnata, and Zea mays. He stated that the insect infests Sorghum bicolor in Northern Nigeria. In the

Sudan, A. varia soccata has been reported to infest wheat in addition to cultivated sorghum and Pennisetum species and the wild grasses of the genus Sorghum (Sorghum purpureo-sericeum) Schmutterer (1969).

In Sahelian areas, particularly Senegal, Mali and Upper-Volta,

A. quadripunctata attacks "mil" (a french name used indiscriminately for both cultivated sorghum and Pennisetum species) Risbec (1950),

Appert (1963), Breniere (1970, 1972). In addition, the insect also 30 attacks "melon" (Risbec 1950).

Damage:

As their names imply, shoot flies destroy the growing apex of the host plant. Breniere (1972) reported that the symptoms of attack appear at the end of the first month of the growth phaseof the host.

After the main stem of the host has been attacked, the central leaves whiten and become yellow and the tillers are subsequently attacked.

Breniere (1972) concluded that the infested plant (sorghum) appears

in a "rosette form". He reported that sorghum is able to recuperate

from infestation occurring at a later stage of the plant growth.

Deeming (1971) stated that once passed a certain stage of its devel-

opment, guinea corn, Sorghum bicolor, shoots cease to be susceptible

to attack by shoot flies. Young (1970) reported that generally

seedlings are very susceptible to larval injury for about four to

six weeks after germination.

In general, the damage of shoot flies is particularly severe on

late sown crops. Breniere (1972) reported experimentation in Upper

Volta has shown that for three different sowing dates, the percentage

of tillers attacked varied from 4% on early sown crops to 30-40% on

late sown crops. Schmutterer (1969) also indicated that up to 90%

or more damaged plants have been observed in late sown crops (central

rainlands of the Sudan). Similar conclusions were reached in Senegal

(I.S.R.A. 1976). However, owing to the tillering ability of the hosts

(sorghum and Pennisetum species), the plants are able to compensate

to some extent for the damage caused by shoot flies (Risbec 1950,

Wheatley 1961). 31

Biology:

Breniere (1972, p.131) pointed out that owing to the lack of

precise information on the shoot fly species involved in West Africa,

"any biological study is indeed of little value". Most of the bio-

logical information reported in the literature deals with A. varia

soccata Rondani. The Symposium held at New Delhi (India) summarized

most of the information regarding shoot flies (Jotwani and Young,

Editors, 1972). Schmutterer (1969) stated that Atherigona spp re-

semble each other very much in appearance and bionomics.

According to Appert (1963), A. quadripunctata Rossi lays its eggs

on the underside of the leaves of the host plant. The egg incubation

period lasts about two days. The larvae, upon hatching, bore into

the shoot of the host (young seedlings) and feed on the internal

tissues of the shoot. Feeding injury results in the wilting and some-

times death of the growing point of the host. The larval period

lasts an average of 17 days and the pupal stage, which is found with-

in the stem of the host, lasts six to seven days.

The bionomics of A. varia soccata Rondani has been reported by

several authors. In Africa, the fly has been particularly studied in

East Africa (Taksdal and Baliddawa 1975, Barry 1972, Swaine and Wyatt

1954, Nye 1960). In the Indian subcontinent, the biology of the fly has been reported by Kundu and Kishore (1970), Moize and Naqvi (1969).

The reviews of Young (1970) and Young and Teetes (1977) summarized

information on the insect in various sorghum growing areas of the world.

The following information deals primarily with A. varia soccata and 32

provides a general review of shoot flies.

Studies of A. varia soccata in East Africa revealed that the in-

sect has a variable life cycle, even within a given country (e.g.

Uganda), suggesting the possibility of different species or biolog-

ical races of the fly (Barry 1972). Swaine and Wyatt (1954) re-

ported that the life cycle of the fly required 16.8 days in Tanzania

(2 days for egg, 8 days for larvae, and 6-8 days for pupae). Nye

(1960) found that the complete life cycle in Kenya lasted 20 days

(3 days for egg, 10 days for larvae, and 7 days for pupae). In

Serere, Uganda, Barry (1972) reported that the life cycle of the fly

lasted an average of 26.9 days (3.5 days for egg, 13.0 days for larvae,

and 10.4 days for pupae). Taksdal and Baliddawa (1975) reported in

Kabaryole, Uganda, that the life cycle lasted an average of 29.5 days

(2-3 days for egg, 19-23 days for larvae, and 5-8 days for pupae).

In the Sudan, Schmutterer (1969) reported that the egg stage of A. varia

soccata lasted about two days, larvae are fully grown in about two

weeks, and the pupal stage takes eight to 12 days during the rainy

season.

In the Indian subcontinent, the complete life cycle of A. varia

soccata required 17-21 days (1-2 days for egg, 8-10 days for larvae,

and 8-10 days for pupae). Kundu and Kishore (1970) reported that A.

varia soccata has four larval instars. In Pakistan, Moiz and Naqvi

(1969) reported that the life cycle of this species requires 14 days

at high temperatures (2-4 days for egg, 6-11 days for larvae, and

6-14 days for pupae). In Thailand, the life cycle of A. varia soccata 33 is completed within three weeks (Sepsawadi et al. 1971).

Adults of A. varia soccata are active mostly during early morning and at dusk. However, in the field, they occur throughout the day (Young 1970). Their behavior is influenced by the prevailing temperatures, which in India, induces two periods of activity(March-

April) and (August-September) (Singh and Sharma 1968). Jotwani et al.(1970) reported that extreme temperatures of 30-44°C. and

2-14°C. have an adverse affect to shoot fly activity. They also stated that ecological factors such as continuous or heavy rains, create adverse affects on the incidence of the fly. Taksdal and Baliddawa

(1975) suggested that the fly emergence may be favored by successful soil himidity. They indicated there was a definite correlation between high infestation of the fly and low rainfall. The adult life lasts two to four days but can reach 12-14 days (Barry 1972, Kundu and

Kishore 1970).

Females of A. varia soccata lay their eggs singly in the lower surfaces of the leaves of the host plants, usually in the seedling stage. The eggs can also be found on the leaves of old plants (Schmutt- erer 1969). Kundu and Kishore (1970) indicated that females can lay

20-25 eggs during a life span of 12-14 days. Young (1970) indicated that usually one or two eggs are found in each plant except in heavy infestations, when the number may reach six or more. Taksdal and

Baliddawa (1975) noted that the four to six leaf stage of the host plant is preferred by ovipositing females and Singh and Sharma (1968) found that crowded plants are also preferred for oviposition. 34

Barry (1972) reported the larval behavior as follows: upon hatching, the larva migrate up over the leaf and down into the center whorl until it reaches the growing tip, where it feeds and passes through three larval stages. The center stem is subsequently killed and other stems are stimulated to produce tillers. Moiz and Naqvi

(1969) and Kundu and Kishore (1970) indicated that no more than one larva or pupa develops per infested seedling. Taksdal and Baliddawa

(1975) reported that one larva is sufficient to cause "dead heart"

(death of the growing point).

The review of Young (1970) reported that larvae complete their development in the decaying plant tissue following the death of the central stem. Kundu and Kishore (1970) indicated that the larva will cut a hole at the base of the stem before pupating. Barry (1972) noted that some larvae may remain quiescent for an extended period and suggested that it may constitute a diapause. It is generally recognized that pupation occurs inside the stem within the lower section of the dead tissue or in the soil near the base of the stem (Barry

1972, Kundu and Kishore 1970, Schmutterer 1969).

In the Sudan, A. varia soccata is reported to occur all year round in the irrigated areas or where cereal crops and grasses are available, but the fly passes the dry season in the pupal stage in rainfed areas

(Schmutterer 1969). In Pakistan, the insect completes 15-16 generations a year and overwinters as larvae in grains or fodder grasses

(Moiz and Naqvi 1969). In India, the larvae are reported to overwintet in sorghum and grasses (Singh and Sharma 1968). In Kenya, Nye (1960) 35 reported that there was no resting stage of A. varia soccata as long as the soil remains moist, but during very dry conditions, the pupae remain below ground level and the fly does not emerge.

Control strategies:

The control of shoot flies is hindered by the species-complex, some of which may occur simultaneously, and the poorly understood taxonomy of this group of pests (Baliddawa and Lyon 1974). Many reported investagations, particularly on A. varia soccata show that:

1. Late sown crops are generally more infested by the fly than are

early sown crops, and irrigated crops suffer more damage than rain-

fed plants (Breniere 1972, Davies and Jowett 1966, Schmutterer 1969).

2. The incidence of attack by the flies is generally restricted to

the seedling stage of the host plant and becomes negligible once

the plant (sorghum) is 14-16" tall (Barry 1972), or mature

(Deeming 1971).

3. Tall and medium sorghum is more capable of recovering from shoot

fly infestation than is very short sorghum (Taksdal and Baliddawa

1975).

4. Closely spaced plants in the four to six leaf stage of growth are

preferred for female oviposition (Singh and Sharma 1968, Taksdal

and Baliddawa 1975).

5. Extreme temperatures and continuous or heavy rains reduce the flies

activity (Jotwani et al. 1970, Singh and Sharma 1968). Periods of

drought increase seasonal incidence of the flies and successful

soil humidity favors adult emergence (Taksdal and Baliddawa 1975). 36

6. Where breeding of the flies is continuous, the flies survive from

crop to crop in fodder grasses, grasses, and grains (Moiz and Naqvi

1968, Schmutterer 1969).

Agronomical and mechanical control:

Among the cultural and mechanical control techniques reported against shoot flies, flooding, adjusting time of irrigation, and man- uring had no significant effect in controlling the pest (Young 1970).

Singh and Sharma (1968) stated that fertilizer had no effect on resistance or susceptibility of sorghum to A. varia soccata. They found that closely spaced plants attracted the female for oviposition and on this basis, they recommended a change in the spacing of plants in

India.

The thrust of cultural methods in controlling shoot flies depends primarily on manipulating dates of planting. In rain-fed crops, it is generally recommended to plant at the earliest feasible time during the season, since it has been shown that the infestation is more severe in late planted crops (Baliddawa and Lyon 1974, Breniere 1972,

Young 1970). Other techniques recommended to control shoot flies are: increased seed rate, removal of injured plants, transplanting seedlings, and identification and destruction of alternative hosts (Young 1970,

Pradhan 1972).

Varietal resistance:

Several studies have been devoted to screening lines of sorghum to identify resistance to the shoot fly, A. varia soccata. Ponnaiya

(1951a, b,) observed in India, that 15 varieties of sorghum were 37

resistant to the shoot fly among 212 types of sorghum he tested. He

attributed the resistance to the presence of irregularly shaped silica

units in the tolerant varieties. Rao and Rao (1956) reported 14

varieties of sorghum that were resistant to the shoot fly among 42

lines tested. Jain and Bhatnagar (1962) also found some resistant

lines of sorghum among sorghum varieties they evaluated.

Singh and Sharma (1968) reported that among 3500 varieties (world

collection) screened under field conditions, 150 varieties showed re-

sistance to the shoot fly, and further screening revealed five varie-

ties to be highly resistant and one highly susceptible. They indicated

that the nature of the resistance was due to antibiosis and tolerance.

Singh et al.(1968) screened 4123 varieties (world collection) of sor-

ghum and reported that 565 varieties in the collection rated high in

resistance to the shoot fly A. varia soccata. They reported that most

resistant species were found in the Conspicuum, Dochna, Caudatum, and

Durra types. They provided a complete list of the genetic stocks

found to be resistant and susceptible to the fly. Jotwani and Srivas-

tava (1970) reported that some sorghum lines may possess high degrees

of resistance to the sorghum shoot fly, but none are immune or com-

pletely resistant.

Blum (1967, 1968, 1969) reported that sorghum resistant to the

shoot fly in India was not resistant in Isreal. He suggested that

different biotypes of the fly may occur in the two. areas. He explained the mechanism of resistance to the shoot fly as "non-preference for oviposition, seedling resistance due to the inability of larvae to 38

penetrate the leaf sheaths, and tolerance by the plants due to resis-

tance of tillers formed after the growing apex is destroyed" (Blum

1968, p.388). He found differences in the amount of lignification

and silica deposition between the observed resistant and susceptible

sorghum varieties, but he could not establish a definite relationship

between the phenomenon observed (silica deposition) and seedling re-

sistance (Blum 1968). He concluded that survival of shoot fly resis-

tant sorghum varieties is associated with lignified tissues at the

central leaf whorl and rapidly growing tillers (Blum 1969).

In East Africa, Dogget et al. (1970) found the two sorghum cul-

tivars, Serena and Namatere, to be good sources of resistance to the

sorghum shoot fly. They suggested that seedling resistance and re-

covery resistance (tolerance) were the main types of resistance to

the sorghum shoot fly. Recovery resistance was the most important

type because it has a high genetic correlation with yield (Starks et al.

1970).

Taksdal and Baliddawa (1975) stated that there was a difference

in the level of resistance (preference for oviposition, antibiosis and tolerance) to the shoot fly among sorghum cultivars. They reported

that tall and medium cultivars are more capable of recovering and the very short cultivars stand up poorly to shoot fly attack. Soto (1974)

stated that non-preference for oviposition appears to be the main

source of resistance to the shoot fly, and while antibiotic factors in sorghum affecting larval instars are present, they operate at a low level. 39

In West Africa, particularly in Upper Volta, Breniere (1972) reported that the Voltaic varieties, Oueni and Bourkou, appear more susceptible to shoot fly than Yifiri or S29. He stated that some varieties (cross between American and Voltaic lines) appeared to be more resistant than their local parents. In Senegal, I.S.R.A. (1976) reported that some varieties of sorghum showed promise for resistance to shoot fly, A. quadripunctata = A. ponti.

Biological control:

The natural enemies of shoot flies appear to be little known.

Young (1970) said that hymenopterous parasites of A. varia soccata were found in India and Morocco. In Northern Nigeria, Deeming (1971) reported the following parasites of A. varia soccata: Pachyneuron sp

(Pteromalidae), Exoristabia deemingui Subba Rao (Encyrtidae) and a

Braconidae gen.n. Alysia. All the parasites were reared from pupae.

Risbec (1950) reported that two pupal parasites, Spanlagia pennisetae

Risbec, and Spanlagia atherigonae Risbec (Hymenoptera) occurred on

A. quadripunctata Rossi.

Chemical control:

The chemical control of sorghum shoot flies, primarily A. varia soccata, was discussed by Baliddawa and Lyon (1974) and Davies (1970).

In Africa, methods of controlling the shoot fly were reported by

Wheatley (1961), York (1967, 1970, 1972), Breniere (1972) and short notes are found in Appert (1963). The last two authors reported on control of A. quadripunctata.

Wheatley reported that dusting around the base of the plant with 40 a combination of DDT/BHC (3:10:0) gave good control if applied weekly, beginning after the plant had germinated and continuing until the plant was one foot high. Appert (1963) recommended dusting the seedl-

ings every six days until they reach 40 cm high, with either Toxaphene

(10% a.i.) or BHC (5% a.i.). York (1972) reported that infestations were reduced by 96% when seeds were dried coated with carbofuran.

Davies reported that endosulfan was an effective control of the shoot

fly but it requires several applications. He recommended the use of

the chemical only for the production of high value hybrid seeds.

Sepswadi et al. (1971) and Meksongsee(1972) reported that carbofuran

as a soil treatment at planting time gave good control of A. varia

soccata in Thailand.

Breniere reported that treatment with carbofuran, phorate and

disulfoton increased seedling emergence, but did not prevent attack by

the shoot fly. He suggested that split applications of phorate may

be required to control shoot fly. In Senegal, I.S.R.A. (1976) re-

ported that seed dressing with carbofuran gave effective control of the

shoot fly A. quadripunctata. Young (1970), Jotwani and Young (1972),

and Young and Teetes (1977) concluded that systemic insecticides may

give better control than conventional foliage sprays or dusts. 41

Contarinia sorghicola (Coquillet)

Diplosis sorghicola Coquillet 1898

Contarinia sorghicola (Coquillet) Felt 1908

Synonyms

Contarinia saltata Felt 1919

Contarinia andropoginis Felt 1921b

Contarinia palposa Blanchard 1958 [Hardy 1960, Harris 1966, Gagne 1973]

Common name: Sorghum midge

Order: Diptera

Family: Cecidomyiidae

Contarinia sorghicola (Coquillet) is one of the major insects

which damage grain sorghum (Young and Teetes 1977). It is one of the

rare insects, along with Atherigona spp which is specific to the genus

Sorghum (Young 1970). Available information indicated that C. sorghi-

cola originated in Africa even though it was first discovered and de-

scribed in North America (Harris 1961a, 1970, Coutin 1969). Barnes

,(1954b, 1956) provided a full account of most Cecidomyiidae which in-

fest cereal crops. Harris (1964, 1966) provided an account of the tax-

onomy of C. sorghicola along with other important Cecidomyiidae.

According to Appert (1963), the insect was discovered for the

first time in Senegal by Leclercq in sorghum in the early sixties. In

the same country, the bionomics and the economic status of the midge

was assessed by Coutin (1970). He concluded that the sorghum midge

damaged a high proportion of cultivated sorghum in Senegal during 1967-

1969. Coutin and Harris (1974) also reported from Senegal the 42 midge C. sorghi (Harris), which is a related species but is confined more to Pennisetum spp (e.g. Pennistumtyphoides). The same authors

(1969) reported Geromya penneseti (Felt), another midge which is a potential threat to millet, Pennisetum typhoides.

Young (1970) reported that nine species of cecidomyiid midges are listed from the earheads of sorghum and closely relatedwild hosts.

Coutin and Harris (1974) suggested that the total numberof cecido- myiids species which develop on sorghum is still unknown. In North

America (Texas), where C. sorghicola has been known for several years, the damage is reported to amount to several million dollars (Gable et al. 1928, Walter 1941, Thomas and Cate 1971). In other sorghum growing areas of the world, the insect is also listed as the key pest of cultivated sorghum (Young and Teetes 1977).

Identification:

Harris (1966, p.315) reported the following combination of characteristics which distinguish the family Cecidomyiidae from other

Diptera:

Larva (third instar).-Small, usually up to 2-4 mm. long, occasionally up to 12mm.; of constant and characteristic form with the thoracic and single supernumerary segments tapering towards the small head capsule, and the nine abdominal segments gradually tapering posteriorly; general body colour ranging through shades of orange, yellow, red and white; characteristic ventral, sclerotised sternal spatula present on the prothorax of most, but not all species; spiracles present on the prothorax and first eight abdominal segments; complex patterns of papillae, spinule rows and other cuticular ornamentation visible in cleared larval skins at high magnifications. Adult.-Small flies, usually 2-5 mm. long, exceptionally up to 15 mm.; antennae long, moniliform, with 6 to 40 segments (usually 14), including scape and pedicel; antennal segments generally bearing whorls of long setae and groups 43

of characteristic sensori ranging from the clusters of simple thin-walled trichoid sensillae of the Lestremiinae to the complex circumfila of many male Cecidomyiinae; eyes well developed, generally holoptic; ocelli present in some Les- tremiinae, otherwise absent; maxillary palps well developed, with 3 or 4 segments, sometimes reduced to 1 or 2, occasionally reduced to a rudiment; wings with relatively simple venation, up to five longitudinal veins (generally fewer), a few or no cross-veins; male genitalia in the form of a bilaterally symmetrical clasper with median aedeagus and various accessory structures; ovipositor relatively simple though often capable of considerable extension; abdomen usually various shades of red, orange and yellow.

The characteristics of the subfamily Cecidomyiinae, tribe Contar-

inii, and the genus Contarinia Rondani are reported by Harris (1966).

Barnes (1954a) stated that the separation of the gall midge (Cecidomy-

iidae) solely on the morphological characteristics is not satisfactory.

Recent accounts on the taxonomy of Cecidomyiidae are also given by

Grover (1966, 1967a,b, 1968, 1970) and Gagne (1973). Anonymous (1975b)

provided a selected bibliography on the taxonomical work of the family.

Grover (1975) provided a key to the Oriental gall midges which included both Contarinia Rondani and Orseolia Kieffer and Massalongo.

The adult C. sorghicola (Coquillet) is a medium small species, with an orange colored abdomen and relatively long antenna, about 1/2

inch long. The female is slightly larger than the male. The female has a well-developed ovipositor and the average wing length is about

1.5 2.0 mm (Appert 1963, Harris 1966, Caresche et al 1969). Under field conditions, the adult female is found generally crawling over the spiklets of sorghum heads during the blooming period (Gable et al.

1928).

The larvae are small, elongate and legless, and about 2 mm in 44 length. At first they are pink but become reddish-orange at a later stage. They lack a sternal spatula (Harris 1966, Caresche et al. 1969).

Passlow (1973) indicated that larvae feed on developing grain and generally are concealed within the floret. Harris (1970) reported that the presence of the midge can often be detected by squeezing the spiklets. The appearance of bright red body contents oozing from the tips of the spiklets indicates the presence of larvae.

The pupa is reddish-brown or black (Caresche et al. 1969). Taley et al. (1971) reported the length of the pupae as 2.009 mm, the width of the thorax as 0.43 mm, and the abdomen width as 0.628 mm. Pupation occurs within the floret.

Taley et al.(1971) described the egg as follows: freshly laid eggs are yellowish-orange and become dark orange before hatching. The egg is more or less cylindrical and measures 0.346 x 0.074. The eggs are laid under the surface of glumes or in the stigma of the ovary.

Distribution:

Barnes (1956) reported that the distribution of the midge is nearly worldwide in sorghum growing areas, and it is likely that the midge was well established in Africa before it was discovered in that continent. Previous distribution of the midge reported by Callan (1945) mentioned that the insect occurred in each of the five continental areas and the Pacific Islands. On the African Continent, the sorghum midge is reported in: Gambia, Central African Republic, Ghana, Kenya,

Nigeria, South Africa, Senegal, Upper Volta, Niger, Mali, Cameroun,

Togo, Sudan, Uganda, and Chad (Caresche et al. 1969, Coutin 1969). 45

The Commonwealth Institute of Entomology (C.I.E.) map 72(A) (1968b) also listed: Ethiopia, Rhodesia, Sierra Leone, Somalia, Zambia, Tan- zania, Zaire and Malawi.

Young (1970) listed the overall distribution of the midge as including the Southern Continental United States, Mexico, Hawaii, South

America, The West Indies, Africa, Italy, Aden, the Indian Subcontinent,

Indonesia, and Australia. The species has also been reported in

Southern France (Coutin 1969).

Hosts:

According to the review of Young (1970), C. sorghicola is generally specific to the genus Sorghum. Bowden (1965) reported that the midge has been reared from a large number of varieties which represent all the subspecies of cultivated sorghum defined by Snowden, and from the wild Sorghum arundinaceum. Barnes (1956) listed as host of C. sorghicola: all varieties of grain sorghum and sorgos (sweet sorghum), broom corn (classified as Sorghum vulgare Pers), Sorghum halepense

Pers (Johnson grass), Sorghum sudanense Stapf (Sudan grass), Sorghum verticilliflorum, Sorghum vulgare, Sorghum caudatum, Sorghum durra,

Sorghum guineense, Sorghum arundinaceum, Andropogon gayanus, Trioda flava (tall red top). Generally all of the reports concluded that cultivated sorghum and wild related grasses are hosts of C. sorghicola (Gable et al. 1928, Caresche et al. 1969, Harris 1964, 1970,

Barnes 1954a, 1956, Geering 1953, Bowden 1965, Young 1970, Hill 1975).

Damage:

The larvae which spend their whole life within sorghum spiklets

(Harris 1970) lacerate the developing ovary in the floret and feed on 46 oozing cell saps (Taley et al. 1971). This results in the failure of grains to develop and they shrivel up and appear "blighted andblasted"

(Caresche et al. 1969, Young 1970). The presence of the damage is first indicated by the occurrence of aborted spiklets associated with reddness of the glumes (Geering 1953). Barnes (1956) stated that the occurrence of sorghum heads with a flattened appearanceis a diagnostic sign of damage. Harris (1970) suggested squeezing the spiklets between the thumb and forefinger as a quick method to detect infestation of the midge. Harris (1971) devised an x-ray method for detecting larvae and pupae of the midge within the spiklets.

Harris (1966) stated that C. sorghicola is the most important single factor limiting the cultivation of sorghum in the West Indies and in the more humid areas of West Africa. He reported (1970) losses in the order of 20-50% in U.S.A., Sudan and Trinidad, and for most

African sorghum growing countries, losses amount to 5-10% loss of grain annually. Taley et al. (1971) reported that the midge has become a serious pest in India since the introductionof hybrid sorghum and damage of 60-95% has been observed in the hybrid sorghum CSH-I.

In Texas (U.S.A.) where the midge has been known for a long time, losses have exceeded ten million dollars annually several times since

1950 (Thomas and Cate 1971). Coutin (1969, 1970) reported that the midge is a severe pest of sorghum in Senegal where 50-90% losses of grain were observed in 1967-1969, and in Chad where up to 80% yield

loss has been reported. Breniere (1970) indicated that serious damage to sorghum was observed due to the midge in late maturing varieties 47 in Mali in 1965, and in Niger and Upper Volta in 1968.

The economic threshold of the sorghum midge has been established at one adult/sorghum head when 50% of the heads have begun tobloom

(Texas) (Bottrel 1971), or when 20-30% of the sorghum heads are in bloom (Young and Teetes 1977). In Mississippi (U.S.A.), the threshold has been reported to be two to three adults/sorghum head (Pitre et al. 1975). In Queensland, Passlow (1960, 1973) stated that control is warranted if the midge population exceeds six females/sorghum head.

Biology:

Several authors have reported the biology of C. sorghicola:

Bowden (1965) in Ghana, Harris (1961b) in Nigeria, Geering (1953) in

East Africa, Coutin (1970) in Senegal, Schmutterer (1969) in the Sudan and Central Africa, Taley et al. (1971) in India, Passlow (1954, 1965,

1973) in Queensland, Parodi (1966) and Overmann James (1975) in South

America, Walter (1941), Gable et al. (1928), Doering and Randolph

(1963), Thomas and Cate (1971) and Bottrel (1971) in North America.

Barnes (1954a, 1956), Harris (1970), Young and Teetes (1977) gave reviews of the midge.

The adult C. sorghicola is reported to be active mainly during morning or evening hours and mates soon after they emerge. Harris

(1961b) reported that both sexes are short lived, and they usually die within ten hours after emergence. Thomas and Cate (1971) reported that males live from a few hours to one day and females die within

24 to 48 hours. Barnes (1956) reported that the adults can live four 48 to five days in cages if provided with sufficient water. Parodi (1966) stated that the sex-ratio indicates a predominance of females over males (45:55, 36:64). Peak emergence of the diapausing midge varies with atmospheric conditions. Passlow (1973) and Harris (1961b) reported that the emergence of adults follows warm weather and sufficient rainfall followed by periods of relatively high humidity.

Oviposition begins shortly after adults emerge, usually during the flowering stage. Adults deposit eggs within the developing flowers.

According to Passlow (1973), in sorghum, eggs are laid before the yellow pollen is shed and during pollination. Doering and Randolph

(1963) found that the greatest oviposition occurred three days after the sorghum heads emerged and was completed after the heads were exposed. Taley et al. (1971) found that infestations of the midge on the cobs at the flowering stage were 100% at the tip, 30% at the middle portion, and 16% at the lower portion. They observed that eggs were laid up to the milky stage of grains, but larvae developing from these eggs did not survive.

The female is reported to lay an average of six to ten eggs (maximum 20) in a single floret and an average of 30 to 35 eggs may be laid by a single female (Taley et al. 1971). Harris (1961b) reported that a single female may lay an average of 50 eggs and Passlow (1973) and

Parodi (1966) reported that a female can lay up to 100 eggs.

According to Barnes (1956), the eggs incubate in 42-60 hours at

86 to 75°F., but at a lower temperature, it requires four days. The incubation period of eggs has also been reported to be two days 49

(Parodi 1966), four days (Harris 1961b), and two to five days (Taley et al. 1971).

Upon hatching, the larva crawls down to the ovary and remains there through its developmental period, feeding on the plant juice

(Barnes 1956, Harris 1970, Taley et al. 1971). Bowden (1965) observed over two seasons, a mean density of 1.7 live larvae/spiklet and a maximum of seven larvae/spiklet. He concluded that despite the several eggs laid in a spiklet, only one larva normally develops in each spiklet. Gable et al.(1928) reported that one larva/spiklet is sufficient to cause complete loss of grain, but as many as eight to ten larvae may develop to maturity on the same seed. The complete larval period in non-diapausing individuals is reported to last seven to eleven days

(Parodi 1966, Gable et al. 1928), ten days (Harris 1961b), eight to thirteen days (10.8 days average) (Taley et al. 1971). According to

Taley et al.(1971), four larval instars develop.

The full grown larvae pupate within the spiklet, but at the time of emergence, they work their way to the tip of the spiklet (Barnes

1956, Gable et al. 1928, Taley et al. 1971). The pupal period is reported to last six to ten days (6.8 days average) (Taley et al. 1971), five to seven days (Harris 1961b), three to five days (Parodi 1966).

Passlow (1973) stated that after adults emerge, tiny pupal cases remain attached to tips of glumes, and if a large proportion of sorghum heads show this sign, it may be too late to save the crop.

The complete life cycle of C. sorghicola (egg to adult without diapause in larvae) lasts 19 to 22 days during the growing season in 50

Northern Nigeria (Harris 1961b); in Northern Ghana, the cycle lasts 17 to 21 days (Bowden 1965), in Uganda 19 to 25 days(Geering 1953), in

India 13 to 32 days (Taley et al. 1971), in Argentina 13 to 16 days

(Parodi 1966), in Texas (U.S.A.) 11 to 21 days (average of 16 days)

(Thomas and Cate 1971), and in Queensland, the cycle lasts 17 to 19 days during summer (Passlow 1973). Young reported that 9 to 12 generations can develop during one growing season.

A facultative diapause may occur in C. sorghicola larvae, en- abling the midge population to survive from one season to the next in areas where prolonged dry seasons or cold winters occur. Some authors indicated that some individuals may stay in diapause for up to two or three years (Young 1970, Barnes 1956, Coutin 1970). Geering (1953) stated that diapausing larvae and their pupal stages lasted 223-227 days (December), 180-189 days (February) and 120-128 days (April). He concluded that climatic changes and probably low saturation periods of air were among the factors terminating diapause. Breniere (1970) re- porting from the work of Coutin, states that larval diapause lasts about eight months in the laboratory, after which humidification of sorghum heads is essential for pupation and eventual emergence of adults.

Harris (1961b) found that adults from diapausing populations emerged after the weekly mean relative humidity exceeded 60%. Barnes (1956) observed that diapause can be broken by wetting the material in which larvae are diapausing, and keeping it at a relative humidity of 94-100% and at 25-30°C. Passlow (1954, 1965, 1973) concluded that adult emergence is induced by a combination of factors such as warm weather and 51 sufficient moisture, followed by a period of high relative humidity.

Some authors indicated that some larvae of every midge generation enter diapause (Passlow 1965, Parodi 1966, Taley et al. 1971). In Senegal, some larvae begin entering diapause from thesecond generation of the midge and may reach 80% of the population by the last midge generation

(Coutin in Breniere 1970).

Control strategies:

Harris (1970) stressed climatic factors, particularly high atmospheric humidity as being the main cause of midge outbreak. He reported that the midge infestation tends to be more severe in low-lying areas such as river valleys which provide longer growing seasonsand many wild hosts of the midge. Bowden (1965) found in Ghana, that the

Guinean savanna zone, with its high humidity, is more favorable to the midge than the much drier Sudan savanna. He indicated that economic damage results from the combined effects of gradual population increase

following emergence and breeding by earlier adults, and more import-

antly from the mass emergence of the majority of adults from diapause

after the temperature and moisture thresholds have been past. In

Senegal, the majority of the midge population emerges 40 days after the

first significant rain following the dry season (Coutin in Breniere

1970).

It has also been reported that there is an importantrelationship

between sorghum midge infestations and the flowering times of the sor-

ghum crops (Harris 1961b, Barrow 1975). Coutin in Breniere (1970) re-

ported in Senegal, that infestations of the midge increase from 20% 52 when flowering occurs in early October to80% when flowering occurs at the end of October or in November.

It is generally felt that infestations ofthe sorghum midge increase with delayed planting dates,longer flowering seasons and mixed varieties. The buildup of the population before sorghum comesinto

flower is largely dependent on the presence of wildhosts, volunteer

or early planted sorghum(Harris 1961b, 1970, Thomas and Cate 1971,

Pitre et al. 1975, Passlow 1954, Bowden 1965). Gable et al. (1928)

and Parodi (1966) reported that wind is the mostimportant factor in

dispersal of adult midge and that flight is in thedirection of pre-

vailing wind.

Agronomical and mechanical control:

As suggested by Barnes (1956), lessening themidge phenology is

the primary target for control.This requires knowledge of the ecolog-

ical requirements of the midge in a given geographical. area. The key

elements in the control are management of wildhosts and planting sor-

ghum so that flowering will occur before the mainpopulation buildup

of the midge. According to Harris (1970), the control should involve

a concerted effort of the wholefarming community in a given area. The

following techniques were suggested by Gable et al.(1928), Walter

(1941), Barnes (1956), Passlow (1973), Harris(1970), and Pitre et al.

(1975):

outside sources of in- 1. The field location should be away from all

festation and designed in a way that prevailing windsblow toward

the source of infestation. 53

2. Elimination from the cropping areas of all nearby wild host volun-

teers, particularly those of the genus Sorghum. Disposal of crop

residues by burning or ploughing before the next growing season.

Management of wild hosts along field borders and where possible,

cutting forage and silage before it flowers.

3. Planting at the most appropriate time to insure an even flowering

period; by sowing pure and uniform seed, and using varieties that

are not prone to tiller. If this is not possible, the planting

date should be scheduled so crops come into flower at the same time

and before the main population buildup of the midge.

4. Spacing the plants to achieve a good yield from the smallest num-

ber of tillers.

Varietal resistance:

Varietal resistance among sorghum species to C. sorghicola has

been reported. Bowden and Neeve (1953) reported that the Nunaba

group varieties show resistance to the sorghum midge. From Brazil,

the sorghum variety AF-28 has been observed to show high levels of re-

sistance to the sorghum midge. The factors contributing to resis-

tance of AF-28 are antibiosis, nonpreference and/or tolerance (Overman

James 1975). In Mexico, Santiago Armenta (1975) stated that diff

erences in susceptibility to the sorghum midge have been found among

15 varieties of sorghum. He listed the varieties N-K-Savanna and

Dekalb -42 as less susceptible to the midge than others. Johnson (1976)

reviewed the work on varietal resistance to the midge in Texas and

found that various lines show resistance to the midge, particularly the 54

Caudatum sorghum types. The most obvious morphological difference between the resistant and susceptible types is their small glumes.

However, there are also indications that under heavy infestations, the midge does not distinguish between susceptible and resistant lines of sorghum. Wiseman and McMillian (1970) found some preference among tested lines even under heavy infestation, but found that most of the sorghum lines were attacked when the midge was abundant. Gowda and

Thontadarya (1975) also found differences in susceptibility among tested lines, but no variety was free from sorghum midge attack.

Harris (1961b) suggested that the midge can adapt its behavior and oviposition on either resistant or non-resistnat varieties.

Biological control:

The impact of biotic factors on C. sorghicola is limited (Barnes

1956). Harris (1961b) indicated that natural enemies have little importance in limiting the initial increase in population of the midge.

In Senegal, Coutin (1970) found the following parasites of the midge larvae: Eupelmus popa Gir and Aprostocetus (Tetrastichus) diplosidis GrwF. The predator, Orius punctaticollis (Reut) (Hemiptera:

Anthocoridae) attacked adults. He concluded that parasitism was low and had little or no effect on population regulation of the midge.

In Queensland, Passlow (1958) noted that one to four larvae and one parasite larva were commonly found developing in the same plant.

He stated that the highest percentage of parasitism was 24.2% with an average of 14.1% of the midge population parasitized in late maturing crops. He found that parasites were of little importance in early and 55 mid-season crops because the rate of parasitism was too low.Young

(1970) concluded that the level of parasitism of the sorghum midge may occur late in the season, but its overall impact in controllingthe midge population is negligible.

Chemical control:

Jotwani and Young (1972) have reviewed the chemical control of C. sorghicola. Their view stressed timing of chemical treatment as the underlying factor in control of the sorghum midge. They reported that research in Texas has revealed that application of insecticides before sorghum panicles have completely emerged from the boot was too early to achieve good control, and treatment three to five days following complete head emergence was too late. Effective control was obtained when treatment was made as soon as possible after complete head emergence.

The recommended procedure in Texas is two applications of organophos- phate insecticides such as disulfoton, carbophenothion, diazinon, or parathion, or a carbamate such as carbaryl (Ward 1975). The first application should be made when 50% of the sorghum heads have just begun to bloom and when one adult midge is found/sorghum head (Thomas and

Cate 1971, Bottrel 1971).

Wiseman et al.(1973) found that in a single application of carbaryl after flowering was completed increased the yield four to seven bushels per acre in Georgia. In the West Indies (Trinidad), a single spray application to sorghum in the mid-bloom stage is reported to give a higher yield of grain than when the heads were sprayed in the early bloom stage (Barrow 1975). Passlow (1960, 1973) found that spraying 56 is of no economic value after flowering has passed its peak and is not justified when midge populations are as low as two females/head.

He suggested (in Queensland) application of D.D.T. or diazinon at

270 g a.i./hectare when the midge population exceeds six females/sorghum head.

In Nigeria, York (1970) reported that the best control of C. sorghicola has been achieved by dusting the sorghum at anthesis with

2 1/2% D.D.T. Coutin (1970), who studied the midge in Senegal, reported that gamma B.H.C. at 250 g/ha applied up to 19 times did not reduce the infestation of the midge below 20%; endosulfan at 500 g/ha applied four times on late sorghum varieties reduced the infestation from 98 to 15%; four applications of fenthion and fentrothion at

650 g/ha were effective against the adult midges, but were phytotoxic to the sorghum, and nine applications of phasolance at 450 g/ha reduced the midge population at the beginning of the season, but by the end of the season, the level of the midge population in treated and untreated plots were the same. He concluded that chemical control, like cultural control, is insufficient when used alone. 57

Orseolia oryzae (Wood-Mason)

Cecidomyia oryzae Wood-Mason 1881

Pachydiplosis oryzae (Wood-Mason) Felt 1921a

Orseolia oryzae (Wood-Mason) Gagne 1973

Common name: Rice gall midge

Order: Diptera

Family: Cecidomyiidae

The rice gall midge has been known for a long time as Pachydiplosis oryzae (Wood-Mason). Recently, Gagne (1973, p.507) placed the genus

Pachydiplosis (of authors not Kieffer) under Orseolia Kieffer and Massa- longo and created the combination Orseolia oryzae (Wood-Mason). The midge is a well-known pest in Southeast and West Asia and in the Indian subcontinent, where the midge damage on rice has been known since 1880

(Reddy 1967). A bibliography of the midge in these areas was provided by Reddy (1973).

In Continental Africa, the economic status of the midge is recognized but not well quantified. Descamps (1956a) reported that the midge in Cameroun destroyed up to 75% of the rice crop in the Logone

Valley in 1954 (North Cameroun). Harris (1960) observed and reared the midge from rice in Northern Nigeria. He concluded that the midge is not expected to become a major pest when vigorous rice is grown and when only one crop is cultivated each season. Risbec (1950) reported identifying the midge from specimens sent from Kayo (Mali). Vayssiere and Galland (1950) reported some damage on rice by the midge in Kayo

(Mali). Recently, Breniere (1969) indicated that the midge occurs 58 in Senegal (Casamance and Eastern Senegal). He suggested that the potential damage to rice caused by the midge could be increased since most countries in West Africa plan to increase rice production by year- round cultivation.

Identification:

The taxonomy of the family Cecidomyiidae has been reported by various authors (listed previously in the description of Contarinia sorghicola). Mani (1934) in Reddy (1967) described the male and female of the rice gall midge and illustrated the male genitalia, the exuvium of the female and the antenna. Perera and Fernando (1969) described and illustrated both larvae and pupae of the midge. Additional descriptions of the immature stages are found in Fernando (1972), and Leuam- sang et al.(1968). Short notes on the midge were reported by Risbec

(1950). Keys to the genera of Cecidomyiidae were given by Grover

(1975) .

Adult rice gall midge is described by Fernando (1972)as being a minute mosquito like insect of orange to orange-brown color in the female and pale brown in the male. Mani in Reddy (1967) gave the size of the male as 3 mm in length and the female 3.5 mm.

Perera and Fernando (1969, p.7) described the larvae and pupae as follows:

All three larval instars are spindle shaped andpossess a reduced head bearing a pair of antennae and a pair of kidney shaped eye spots mid-dorsally on the second segment of the body which is thirteen segmented. The first instar larva is characterized by the possession of two pairs of short spines borne laterally on tubercles on the penulti- mate segment and four pairs of spines on tubercles on the last segment of which one pair of spines is considerably 59

longer than the others. The second and third instar larvae do not possess spines on the pennultimate segment and the last segment bears only 3 pairs of short spines. The third instar larva is characterized by the possession of a heavily chitinized Y shaped sternal spatula located mid-ventrally between the second and third segments. The pupa is characterized by the possession of a pair of heavily chitinized cephalic horns each bifurcating into a pair of spines. Two similarly chitinized horns are borne, one each below the compound eyes. A pair of fine spines are located in the post-occipital region while a pairof thicker spines is located on the margin of the mesothorax. Minute spines are located in numbers at the posterior margins of the first seven abdominal segments. The male pupa can be distinguished from the female pupa by the abdomen being shorter than the posterior extension of the legs and the presence of claspers which are visible through the pupal skin at the posterior end of the abdomen.

The dimensions of the larvae given by Fernando (1972) are: 0.50 x 0.127mm for the first instar; 1.5 x 0.4 mm for the second instar; and 3.2 x

0.8 mm for the third instar. Risbec (1950) reported that larval length may reach 4 mm and is reddish in color (presumably the last instar).

The eggs are described as being elongate, reddish-brown and reaching 0.44 x 0.25 mm (Fernando 1972). The immature stages, with the exception of eggs, develop inside a gall which is induced by larval feeding at the base of the apical meristem of the rice plant (Perera and

Fernando 1969, 1970, Fernando 1972, Barnes 1956). Previous descriptions of the immature stages by several authors are found in Reddy (1967).

Distribution:

The review of Reddy (1967) listed the rice gall midge as occurring in south and south eastern Asia and in Africa, particularly in Burma,

Ceylon, China, India, Indonesia, Nigeria, Northern Cameroun, Sudan,

Thailand, and Vietnam. Grist and Lever (1969) listed the following countries in which the rice gall midge occurs: India, Pakistan, Ceylon, 60

Burma, Taiwan, Cambodia, Vietnam, Malaya, Java, Mali, Nigeria, Cameroun, southern Sudan and Thailand. A complete list of the midge distribution is given in the C.I.E. map 171 (1963).

The midge is reported from Mali by Risbec (1950), and Vayssiere and Galland (1950). Breniere (1969) reported the rice gall midge from Senegal (Casamance and eastern Senegal), Ivory Coast, and Kaye,

Mali (southern section of the Senegal valley). Harris (1960) suggested that the insect can be considered well-established in the Sudan and Guinea zone of Tropical Africa.

Hosts:

Wild and cultivated rice are considered to be the main host of

Orseolia oryzae. The status of alternative hosts of the midge is still controversial. Barnes (1956) listed the following hosts of the midge:

Oryza sativa (irrigated, swamp and upland rice), Panicum stagninum,

Panicum congregatum, Ophiurus corymbosus, and Paspalum scrobiculatum.

He stated that the eggs of the midge were found on Paspalum orbiculare,

Panicum repens and Zizania latifolia, but raised doubts on many of the above reported alternative hosts. Bakhsi (1974) studied the host plant range of the rice gall midge, particularly with Oryza sativa,

Cynodon dactylon, and Paspalum scorbiculatum. He concluded that the midges breeding on paddy (rice) and different grasses are host specific and under normal conditions do not change their hosts. Similar studies were made by Bhamburkar et al.(1971) and they found that only the gall fly from wild rice could produce galls on cultivated rice. They also concluded that the pest remains on wild rice during the non-cropping 61

season or in green stubble when fields stay wet enough to allow it,

otherwise, wild rice is preferred. Israel et al.(1970) listed many

weeds as potential hosts of the rice gall midge, but stated that only

in Mnesethia laevis did cross infestation studies confirm the identity

of the midge. Reddy (1967) suggested that resemblence of the galls

on alternate host plants with those on rice plants may not be an indic-

ation that Pachydiplosis oryzae (=Orseolia oryzae) caused the gall

formation.

Damage:

The damage on the rice plant caused by the midge results from the

larval feeding on the apical meristem which subsequently develops into

a gall instead of an ear bearing stem (Fernando 1972). When the grow-

ing point of the plant is destroyed, the leaf sheath of the highest

leaf develops into a long hollow cylindrical tube called "silver shoot"

or "onion shoot" (Barnes 1956, Grist and Lever 1969).

Israel and Prakasa Rao (1968) reported that infested rice plants

react by producing tillers, which, if attacked produce additional till-

ers. Severe infestation results in a prolonged tillering phase, stunt-

ed growth, delayed flowering, and uneven maturity, giving a bushy

appearance to the plant. They concluded that the overall end result

of infestation from the midge is reduction in yield.

Perera and Fernando (1969, p.9) stated that Pachydiplosis oryzae would develop and induce gall formation in any meristematic region,

except in roots. They explained the gall formation in the plant as 62

consisting of:

a. suppression of leaf primordial differentiation at the growth cone, b. cell proliferation in a specific zone on the inner surface of the innermost leaf primordium, in the form of radial ridges that grow and in a fuse forming the gall primordium which enclose the developing larva, c. elongation of the gall primordium following pupation.

They suggested that the development of the gall is brought about by the diversion of nutrients from the apical meristem to the larva, and poss- ibly, substances produced by first instar larva and prepupa. In addition, nutrient flow after the larva has stopped feeding could account for the growth of the radial ridges and the gall elongation. They also reported that recovery of infested plants could occur if the infestation is controlled before the second instar larval stage, but the plant will not recover after the larva reaches the third instar.

In south and southeast Asia, the rice gall midge is reported to cause 60% loss in yield of rice in different regions (Israeland Pra- kasa Rao 1968). Shastry et al.(1972) reported in India, that loss in rice yield can range from 15-100%, depending on location, season, varieties, and time of planting. Israel, Vedamoorthy and Rao (1959) in Reddy (1967) found for every unit increase in the incidence of the rice gall midge, there was a corresponding loss of 0.502% in the yield. Descamps (1956a) reported from North Cameroun, that the midge caused 75% loss in rice yield. Even though damage incidence is not quantified in West Africa, the potential of the midge threatening rice crops, particularly under continuous cultivation, was expressed by Breniere (1969) and Harris (1960). Sampling schemes for estimating infestations and field losses from the midge were given by 63

Singh et al. (1972).

Biology:

The main biological characteristics of the rice gall midge have been reviewed by Barnes (1956), Reddy (1967) and Pathak (1968). Prasad

(1968a,b, 1969a,b) summarized the biology of gall midges in general and listed some control measures. Breniere (1969) gave a background account of the midge in West Africa.

Adult midges are nocturnal in habit. They rely on plant juices and moisture from water droplets on the leaves of the host plant for survival. Emergence from the pupa occurs at night and at early dawn, and is followed shortly by copulation. The adult lifespan varies from one to five days and females live longer and out number males in the field (Reddy 1967, Barnes 1956, Pathak 1968). Fernando (1972) reported that male emergence and survival decreased when humidity was low and temperature was high. He concluded that temperatures ranging from

20.5°C. to 27°C. and 75-79% relative humidity were optimum conditions for adult survival in the laboratory.

The eggs are laid singly or in a group on various parts of the hosts. According to Reddy (1967), eggs may be deposited at the base of the plant, on the stem of rice seedlings, sheathes, ligules of the leaf, undersides of the leaf blade and occasionally on standing water. The potential egg laying capacity of the individual female is variable. Fernando (1972) reported that 175 to 200 eggs are laid on the,first night of emergence. Leuamsang et al.(1968) found that a minimum of 19 and a maximum of 251 eggs, with an average of 136 64

eggs could be laid per female. Pathak (1968) reported that the individual female is able to lay from 100 to 200 eggs. The incubation period of eggs was found to last three to four days in India and three to six days in China (Reddy 1967). In Thailand, the incubation period ranged

from three to.five days (Leuamsang et al. 1968). Fernando (1972)

found that relative humidity over 90% was essential for a normal hatch

in the laboratory.

The development and behavior of the larvae was reported by Perera

and Fernando (1969, 1970), and Fernando (1972) as follows: the first

instar larva upon hatching moves from the oviposition site to the ter-

minal or axillary shoot apices to which they are attracted.They do

so without boring into the plant tissue. They feed at the base of the

apical meristem which induces the gall to form, and subsequent larval

instars remain therein and feed at the base of the growth throughout

their development. Larvae which infest terminal shoot apices develop

normally but arrested growth or dormancy occurs in larvae which in-

fest axillary buds and their growth is resumed only after the active

growth of the buds. Several larvae may infest one shoot apex, how-

ever, only one larva develops within it after the third instar is

reached. Pathak (1968) and Barnes' (1956) reported that only one larva

develops per infested tiller.

The review of Reddy indicated that the first instar larva is able

to survive in water for a period of up to six days. Descamps (1956a)

reported that the young larvae can enter water and infest the rice

plant. The larval period observed by several authors varied from 65 six to 33 days (Reddy 1967). Pathak (1968) reported that the period lasted an average of 15 to 20 days. Perera and Fernando (1969) and

Fernando (1972) reported that there are three larval instars, and a short prepupal period (24 hours). They indicated that humidity over

95% and a moist surface are essential for the first instar larvae to survive and successfully infest young rice plants.

The full grown larva is reported to pupate within and near the base of the formed gall. The built-in series of heavily chitinized spines allow the pupa to reach the top of the gall and to pierce a hole for the adult emergence (Reddy 1967, Fernando 1972).The pupal period lasts from two to eight days (Reddy 1967, Pathak 1968).

Larval diapause has been reported in the rice gall midge. This allows the insect to survive in unfavorable seasons. Descamps (1956a) reported that the midge infest the wild rice (Oryza barthii) after the main crop is harvested. The larvae progressively enter diapause as weeds dry up, but the development can also proceed during the dry season, provided there is sufficient moisture. Otherwise, diapause con- tinues for some months and larvae only resume their activity after the rains begin. In other areas, the larvae are reported to overwinter in rice stubble and grasses, or they remain quiescent in nascent buds underground (summer) and develop with the bud's growth after the rains begin (Reddy 1967). Perera and Fernando (1970) suggested that larval dormancy in inactive axillary shoot apices may explain the seasonal survival of the rice gall midge.

The complete life cycle of the rice gall midge requires 19-26 days 66 on rice and-9-14 days on grasses (Katarki and Bhagarat 1960). Israel

et al. (1970) indicated that the life cycle lasts 21 days on riceand

24 days on weeds. In India, the complete life cycle (egg to adult

emergence) required two to three weeks, and five to eight generations of the midge are produced each year (Reddy 1967). In Thailand,

Leuamsang et al.(1968) stated that the complete life cycle takes 26

to 35 days at an average temperature and relative humidity of28.2°C.

and 73% respectively in the insectary. Descamps (1956a) stated that

in north Cameroun, the life cycle requires 25 days in August. Pra-

kasa Rao, Rao and Israel (1971) reported that the lower and upper

threshold temperatures for development of the midge are 16°C. and 34°C.

respectively. The review of Pathak (1968) indicated that 26 to 30°C.

and 82 to 88% relative humidity are favorable for the midge development.

Control strategies:

The reviews of Reddy (1967), Pathak (1968) and Barnes (1956) and

studies of Prakasa Rao, Rao and Israel (1971), Wickramasinghe (1969),

Rao (1975), Katiyar et al.(1971), Israel et al. (1970) and Chelliah

and Subramanian (1973) pointed out some of the factors which favor

heavy midge infestations. They are summarized as follows:

1. The midge activity intensifies at the onset of the rainy season;

some generations of the midge can develop on wild hosts and later

transfer to cultivated rice. Generally, abnormally wet weather

and late planting of the crop are conducive to heavy infestation

by the midge, whereas, dry weather has the reverse effect. 67

2. The midge is able to infest both nursery and field rice. The

tillering stage of the plant is the most favorable period for

infestation, which increases the number of tillers but not the

yield.

3. The midge incidence is more pronounced in humid areas such as

low lying areas, or river valleys. In Thailand, the midge is

primarily observed in districts through which rivers pass

(Kovitvadhi and Cantelo 1966).

4. Soil pH may effect the midge infestations. Alkaline soils are

reported to support a higher population of the midge. Increasing

levels of either nitrogenous fertilizer or potash fertilizer in-

crease infestations of the midge, but phosphate in combination

with nitrogen has the opposite effect.

5. Continuous standing water favors heavy midge infestations; rice

growing up to 45-60 cm in water can be infested by the midge (Rao

1975).

6. The pest survives between rice crops in weeds, wild rice, self

sown rice, or rice stubble left to sprout. Wild rice is the most

preferred alternate host if sufficient moisture is too low to

allow cultivated rice stubble to stay green (Bhamburkar et al. 1971).

Survival of the pest can also be achieved through diapausing larvae

in partly buried galls such as in Panicum sp (Israel et al. 1970),

Oryza barthii (Descamps 1956a), or through larval dormancy in in-

active axillary shoot apices of the rice plant (Perera and Fernando

1969, 1970). 68

7. Pathak (1968) stated that the rice gall midge seldom attacks the

second or third rice crop. Breniere (1969) indicated that in

West Africa, the second rice crop can be heavily attacked by the

midge, particularly if grown at the beginning of the dry season

and under irrigation.

Agronomical and mechanical control:

Various techniques have been put into use for control of the rice gall midge. The review of Reddy (1967) reported measures such as: removal of infested plants and their destruction before the pupal stage of the midge, destruction of stubble by either burning or ploughing, and weeding out alternate hosts. Generally, the best control measures involve early planting of the rice crop and/or the use of early maturing varieties along with good fertilization. The main objective of early planting is to escape the major population buildup of the midge. Patel, Bhat and Gokavi (1957) suggested that draining rice fields may be a possible method for controlling the midge when infestations are severe in irrigated rice. Shastry et al.(1972) reported that some farmers often grow seedbeds of photoperiod sensitive varieties prior to heavy pest incidence. Thus, they transplant over-aged seedlings (50-70 days old) which allows the mother tiller to escape infestation and produce panicles.

Varietal resistance:

Several authors observed that high yielding rice varieties are more susceptible to midge damage than local varieties grown under local conditions (Katiyar et al. 1971, Reddy 1967), and levels of the midge infestation vary with varieties under similar fertilization programs 69

(Chelliah and Subramanian 1973). Patel, Bhat and Gokavi (1957) reported that the rice variety "faya" resists infestation of the rice gall midge in Nyassaland. Bhat, Patel and Gokavi (1958) found that early maturing rice varieties show less infestation, but there was no difference among the middle and late maturing groups. However, they found one late variety (Ratnachudi) which was more resistant to the midge than the improved varieties, although it yielded 20% less.

Shastry et al. (1972) reported that 246 rice varieties among the F.A.O. and C.R.R.I. genetic stocks had some degree of resistance to the rice gall midge. Field screening at Warrangal, India, confirmed the resistance in the varieties Esawarakora, HR 42, HR 63,

Ptb 18, Ptb 21, and Siam 29. The variety Esawarakora was used as a donor parent to produce among others, W1263, which was observed to be highly resistant to the midge and was used in breeding programs in

India, Ceylon, IRRI, and Thailand. Plodder and Alagoda (1972) found that W1263 seedlings were not resistant to oviposition of the midge, but they inhibited the transformation of first instar larva to second instar larva at their terminal apices. They suggested the resistance may be explained by the concentration of factors or substances in the tissue of some rice varieties, indicating that antibiosis could be the mechanism of resistance in the variety W1263.

Wickramasinghe (1969) stated that varieties like H4, Taichung native

1, and IR 8 are susceptible to attack from the rice gall midge, owing to their high nitrogen responsiveness and tillering abilities. Pre- vious investigations on varietal resistance to the rice gall midge are 70

found in Reddy (1967).

Biological control:

The rice gall midge is reported to be controlled by its natural

enemies. In Southeast and West Asia, Platygaster sp are major para-

sites among the complex parasites of the midge. Up to 80% parasitism

occurs in some areas (Reddy 1967).

In Continental Africa, Descamps (1956a) looked at the parasite

complex in Northern Cameroun and found that up to 20% of the larvae

are parasitized on cultivated rice by Tetrastichus pachydiplosisae

Risbec. Platygaster diplosisae Risbec destroyed up to 38% of the

active larvae, and 50-60% of those entering diapause in the wild rice

Oryzae barthii. He also found that diapausing larvae are parasitized

by Aplastomorpha camerounensis Risbec, and a Bracon sp (near Bracon

annulicornis (Brues). Breniere (1969) reported from the Ivory coast

that a Platygaster sp parasitized large numbers of larvae towards the

end of the rainy season. In Kayo, Mali, Risbec (1950) reported

Tetrastichus sp as a parasite of the rice gall midge.

Chemical Control:

Bhamburkar et al. (1971, p.40) stated that three soil applications

of thimet (Phorate 10% granule) at 4 kg per acre controlled 98-99% of

the midge when applied as follows: "(1) at the time of sowing seed nur-

sery,(2) 8-10 days after transplantation,(3) 25-30 days after transplantation". Prakasa Rao (1970) and Satpathy (1970) observed that granular endrin applied in irrigation water at 1.5 kg/ha, 10, 30, and 50

days after transplanting rice plants was effective to lower the midge 71

infestation and increase yield from 1.46 tons/ha to 2.04 tons/ha.

Hidakat et al.(1974) said that in Thailand, Diazinon granules

applied at 2 kg/hectare gave excellent control of the rice gall midge.

In West Africa, Breniere (1969) indicated that research in the

Ivory coast has shown that adding B,H.C., and granular Diazinon to

irrigated water reduced infestations of the rice gall midge and

substantially increased the yield. Reddy (1967) suggested that

accurate timing of the chemical treatment is necessary for effect-

ive control, and generally, application of insecticides by means

of low volume spray at the peak of the midge infestation gives the

best control. 72

Lepidoptera

Acigona ignefusalis (Hampson)1

Proceras ignefusalis Hampson

Diatrea ignefusalis (Hampson)

Chilo ignefusalis (Hampson)

Coniesta ignefusalis (Hampson)

Acigona ignefusalis (Hampson)

Synonyms

Chilo pyrocaustalis Hampson (misidentification)

Coniesta pyrocaustalis (Hampson) (misidentification) [Anonymous 1954, Grist and Lever 1969, Bleszynski 1970] Order: Lepidoptera

Family: Pyralidae

Subfamily: Crambinae

Acigona ignefusalis (Hampson) has been reported in Senegal by

Risbec (1950) and Appert (1957) under the name of Chilo pyrocaustalis.

Appert (1963, 1964) treated the insect under the name of Coniesta ignefusalis. The same name, Coniesta ignefusalis was used by Harris

(1962), who did most of the biological investigations of the insect in Northern Nigeria.

Harris (1962) reported that the insect is the major factor limiting yield of millet in some areas of Nigeria. Breniere and Coutin (1969)

'Taxonomic treatment of this species was not found during the survey of literature. According to Bleszynski (1970) what has been called Chilo pyrocaustalis is referable to Acigona ignefusalis (Hampson). 73 classified A. ignefusalis as the most important stem borer of millet in Eastern Senegal (Sinthiou-Maleme), and Schmitz (1969) found the insect to be the most damaging pest of rainfed millet in some segments of the Senegal River Valley (Kaedi).

Identification:

Bleszynski (1969, p.32) described the genus Acigona Hubner as follows:

Ocelli fully developed, moderate, vestigial or completely absent. Face rounded, more or less produced, or strongly conical, often with a corneous point and ventral ridge. Forewing with R1 free or coincident with Sc., R2 free or stalked with R3 - R5. R5 in most species free, but one American species and one African species stalked with R3- R4. M2 free. In hindwing cell open. Frenulum in female double or triple, sometimes the same specimen shows one hindwing with double and the other with triple frenulum. Forewing unicolorous or with Chilo-type pattern; many species show two transverse lines, discal dot and terminal dots, venular and intervenular lines. Male genitalia: valva always with well developed costal-basal process (pars basalis), uncus and gnathos well developed, pseudo- saccus and saccus absent, vinculum large with complex mus- cle attachment, aedoeagus in most species with no cornuti. Female genitalia: posterior apophyses strongly dilated, papillae anales often stout, 8th tergite linked to ostium pouch by a narrow bridge. Bursa copulatrix often with one or two signa.

Risbec (1950, p.74) reported the adult characteristics as follows: female adult is about 12-14 mm in body length, with a span "envergure" of 26-30 mm. The male is smaller; 10 mm in body length, with a span of 22-25 mm. The general color is golden brown in the forewing

"jaune paille", and the hind wing is hyaline "blanchatres presque incolore".

The larvae attain 17 mm when full grown (Risbec 1950). Harris

(1962) indicated that two types of larval color occur, depending 74 whether or not the larvae are diapausing or non-diapausing. He stated

that the diapausing larvae (during the dry season) are uniformly pale

yellow to cream-white, but non-diapausing larvae (during rainy season)

are black spotted. The pupa is ten to 17 mm long, and is equipped with

two strong pairs of spines in the cremaster. The stage occurs within

the stem of the host (Risbec 1950).

The eggs are cream-yellow when freshly deposited, but darken

later. They are oval in shape with no sculpture in the chorion and

are deposited in batches between the leaf sheath and stem of the host

(Risbec 1950, Harris 1962).

The immature and adult stages are illustrated in Harris (1962).

Appert (1964) illustrated the venation pattern of pyralid and noc-

tuid stem borers of cereal, to assist in distinguishing the two groups.

Bleszynski (1969) provided keys to the genera of the subfamily

Crambinae.

Distribution:

Bleszynski (1969) stated that the genus Acigona is distributed in

the Paleartic, Ethiopian, Indian, Australian, Neartic and Neotropical

regions, but most species occur in the subtropics and tropics.

A. ignefusalis is reported mainly from West Africa. Harris (1962),

Breniere (1970), Grist and Lever (1969) and Appert (1964) listed the

following countries in which the moth is distributed: Gambia, Ghana,

Mali, Niger, Nigeria, Upper Volta, and Senegal. Schmitz (1969)

reported the moth as occurring in Mauritania (Kaedi). The moth

is not listed among the insect pests occurring in East Africa (Nye 1960), 75 and Schmutterer (1969) does not list the moth in Central and North- east Africa.

Hosts:

The host plants which are recorded for A. ignefusalis are all in

the Graminae family. Harris (1962) and Appert (1963, 1964) listed

the host plants as follows: Sorghum vulgare, Pennisetum typhoides,

Oryza sativa, Zea mays and Saccharum officinarum. Among the grasses,

the list included: Panicum maximum and Andropogon sp. Gregory

(1954) recorded, in addition to the above cultivated crops, Digitaria

ibura, and Forsyth (1966) listed Pennisetum cinerens.

Damage:

Bleszynski (1969) divided the larvae of Crambinae species into

those which defoliate grasses and mosses and those which are stalk

borers of grasses. Acigona species belong in the last category.

Damage from Acigona spp results from larvae tunneling in the stem.

This weakens the host and interfers with the vascular system of the

plant, which prevents grain formation (Harris 1962).

A. ignefusalis is considered the most specific in regards to its

host selection among the stem borers of cereal crops. Harris (1962)

observed both interspecific and intraspecific selections of plants by

the moth. He reported that the insect tends to be confined in millet

(Pennisetum typhoides) more than other host plants, and within the

millet, the moth selects larger and older plants for oviposition.

Risbec (1950) also indicated that varieties of millet (Sanio and Souna)

are frequently more damaged by the insect than are sorghum species. 76

The severity of damage from A. ignefusalis is generally considered higher in late sown crops or late maturing varieties during the rainy season. Anonymous (1954) reported in Ghana, that loss due to

the moth is no less than 5% and sometimes more, particularly in late millet. At a density of three larvae/stem, grain production was reduced 54% (Anonymous 1954). Harris (1962) reported in Northern

Nigeria, that loss in early millet is seldom significant, but major

loss may occur in late planted crops. Breniere and Coutin (1969)

found in Eastern Senegal (Sinthiou-Maleme), that A. ignefusalis devel-

oped three generations during the cropping season (rainy season).

They observed when staggering the planting date of millet crops, that

the last sown plants supported the heavier infestation. They concluded

that early maturing varieties (Souna) are less infested in comparison

to late maturing varieties (Sanio), although the latter varieties are

able to tolerate heavy infestations of the moth.

Biology:

Notes on the life history of A. ignefusalis are given in Risbec

(1950), Appert (1963, 1964, 1957), Breniere and Coutin (1969) and

I.S.R.A. (1975, 1976), but the most detailed studies have been report-

ed by Harris (1962). Unless otherwise stated, the following account

is from Harris (1962).

The adults are active shortly after they emerge, which is during

the night. In the day they are inactive and lie unnoticed on the low-

er surfaces of leaves or along stems. The adult life span is about

six days with a preoviposition period of about two to three days. 77

The oviposition period may last through the adultlife.

The eggs are laid in groups of 20 or 50 (Harris1962, Risbec

1950). The individual female lays 100-200 eggs. The incubation period is about nine to 12 days (Harris 1962), or seven tonine days as reported by I.S.R.A. (1975). The eggs are deposited between the stem and leaf sheath.

Upon hatching, the larvae remain clustered at first,then start

tunnelling the leaf sheath and the underlying stem one daylater.

Within the plant tissue, the larvae move by active and passive trans-

port. The passive transport is due to the growing tissueand the

active transport is due to the tunnelling of the larvae. Thus, un-

like other stem borers, the larvae of A. ignefusalis can befound at

a higher level in the plant than thehatching site. This habit is

not observed in rice plants (Grist and Lever1969). Dispersal of

larvae between plants is limited. A density of three larvae/plant is

considered normal in infested plants (Anonymous 1954). Harris (1962)

and Risbec (1950) indicated that infested plantsgenerally have a

high larval density, and up to 3.98 larvae andpupae/stem of infested

millet was found by Harris (1962). The dispersion of larvae within

the plant can delay the sign of infestation and may preventinjury to

the growing point of larger millet plants.

Duration of the larval period depends on whether or not thelarva

is diapausing or non-diapausing. Harris (1962) noted that the larval

period in the rainy season lasted 30-40 days, with a mean of34 days.

At the onset of the dry season, the larva enters a facultative 78 diapause which can last up to six or seven months, and occasionally more than a year. I.S.R.A. (1975) found the larval period in the laboratory lasted 26 days. The report indicated the presence of a facultative diapause in A. ignefusalis larvae. It also reported

(1976), that percentage of pupation in diapausing larvae increase with increasing moisture (45% pupation at 5 mm and 75% pupation at

5 x 10 mm). The report stated that in natural conditions, larval diapause was terminated by the first significant rainfall in Bambey,

Senegal.

Usua (1970b) studies larval diapause in a similar species,

Bussoela fusca (Fuller) (Nouctuidae). He stated that larval diapause was not necessarily linked to the season, but that it occurred throughout most of the year, even when the host (maize) was actively growing.

He reported that water did not terminate diapause in the field, but appeared to increase the emergence of the adult after larval diapause had been completed. He noted that diapausing larvae feed throughout the period, but about 82% less than non-diapausing larvae. He found that larval pigmentation is a function of the host quality, e.g. pigmented non-diapausing larvae occur when the host is young or mature but still fresh, and non-pigmented diapausing larvae occur when the host is dry. He concluded that diapause may not be responsible for larval coloration, and suggested genetic mechanisms or heredity controls diapause.

Mature larvae of A. ignefusalis pupate within the host stem.

According to Harris (1962), the male pupal period lasted an average 79 of 9.3 days and an average of 9.7 days for the female pupa. Risbec

(1950) indicated that the pupal period lasted nine days, and I.S.R.A.

(1975) reported eight days for the period.

The life cycle of the moth is completed in 57 days (without diapause) in Northern Nigeria (Harris 1962), and 36-46 days (average of

41 days) in Senegal in the laboratory (I.S.R.A. 1975). Six to seven larval instars develop during the life cycle (Harris 1962). In Senegal and Northern Nigeria, A. ignefusalis develops three generations during the rainy season (Breniere and Coutin 1969, Harris 1962).

Control strategies:

The observations of Harris (1962), Breniere and Coutin (1969),

I.S.R.A. (1975, 1976) and I.R.A.T. (1971) revealed some of the characteristics which determine the incidence of A. ignefusalis. They are summarized as follows:

1. The larvae survive the dry season mainly in crop residues from

the preceeding growing period (rainy season) and particularly in

millet stem stool.

2. The larvae tolerate high temperatures and low humidity. Harris

(1962) noted that stems stalked in the field or used in construct-

ing houses are a major source of infestation.

3. Diapause is terminated by rainfall of 100 mm, high relative hu-

midity and at temperatures not exceeding 40°C. (I.R.A.T. 1971),

or following the first significant rain following the dry season

(I.S.R.A. 1976).

4. Late sown crops during the rainy season are heavily infested and, 80

while sorghum species may not be severelydamaged, millet (Pennise-

tum typhoides) may bevirtually destroyed.

such as Souna, suffer less damage 5. Late maturing millet varieties

from A. ignefusalis than later maturingvarieties such as Sanio.

develop during the rainy season. 6. Three generations of the moth

During the second generation, thepopulation causes significant

damage on the millet crops, and bythe third generation, the plants

may be completelydestroyed.

Agronomical and mechanical control:

Harris (1962) suggested the followingmethods to control A. ignefusalis in Northern Nigeria: (a) removal and destruction of stems and stools of cereal crops, (b)cleaning up fields after harvest,

son, and (d) if stackingthe stems is practiced, they shouldbe stack-

ed in small stacks and left in the openrather than in shaded areas.

Ploughing and burning crop residuesdestroys large number of

"overwintering" diapausing larvae found instools (Anonymous 1954).

This method of control was also suggestedby Appert (1957) and Risbec

(1950).

Planting at the earliest feasible timeof the rainy season and/or

using early maturing varieties arealso suggested. Breniere and Coutin

(1969) found damage from A. ignefusalis was more severein the early

maturing varieties (Souna) sown July8th and 19th, than the same var-

ieties planted June 21st and 27th duringthe same growing season

(Eastern Senegal). It is also found in Senegal, the latematuring 81 millet varieties (Sanio) are most heavily infestedby A. ignefusalis thant the early maturing varieties (Souna) (Risbec 1950,Appert 1963,

Breniere and Coutin 1969).

Varietal resistance:

I.R.A.T. (1971) reported that millet varieties werefound to show

some degree of resistance to A.ignefusalis in Niger. It listed the

following varieties in order of decreasing resistance: P3KOLO, Zonge,

Souna 3, Mil de Dori, HK Synthetic Niger, Synthetic 1 Kano,Ex Bornu,

and M2 Ghana.

In Senegal, the variety "Mil cerealier Gam" is more susceptible

than the variety "Mil Souna 3" (I.S.R.A. 1976). Breniere and Coutin

(1969) and Breniere (1970) reported that the late maturing Sanio var-

iety showed more resistance to A. ignefusalis than the early maturing

variety, Souna. They suggested that resistance might be due to the

greater height and more biomass of the Sanio variety.

Biological control:

Harris (1962) listed Syzeuctus sp. (Icheumonidae) as the most im-

portant parasites of A. ignefusalis in Northern Nigeria. Other para-

sites include: Sturmiopsis parasitica (Curran) (Tachinidae),

Tetrastichus atriclavus Wtstn.(Eulophidae), and Hyperchalcida

soudanensis Steffan (Chalcidae). He noted that the overall rate of

parasitism in both pupae and larvae seldom exceeded 10%.

Risbec (1960) reported the following parasites of A. ignefusalis

in Senegal: Syzeuctus sp. (Icheumonidae); Euvipio fascialis

Szepligeti, Apanteles sesamiae Cameron and Rhaconotus soudanensis 82

Wilkinson (Braconidae); Euchalcidia soudanensis Stefan =Hyperchal- cidia soudanensis (pupal parasite) (Chalcididae); Euzkadia(integralis)

Mercel (larval parasite) (Encyrtidae); Platytelenomus hylas =Teleno- mus hylas Nixon (egg parasite)(Proctotrupidae = Scelionidae);

Goniozus sp. (larval parasite) (Bethylidae). Risbec (1950) suggested

that the overall effect of parasitism is variable in Senegal.

Chemical control:

Grist and Lever (1969) suggested Endrin and Sevin to controlA.

ignefusalis infestation in rice crops. York (1967, 1970) reported

that Endosulfan (= Thiodan) and Azodrin applied as granules or spray,

or 5% DDT dust can effectively controlcereal stem borers. Bouriquet

(1963) reported that Endrin or Dieldrin applied as granulars or as a

dust can also be effective against stem borers.

In Senegal, experiments with Carbofuran (= Furadane)and

Endosulfan to control A. ignefusalis showed inconclusive results

(Breniere and Coutin 1969, I.S.R.A. 1976). 83

Chilo zacconius Bleszynski

Chilo zacconius Bleszynski 1970

Common name: none

Order: Lepidoptera

Family: Pyralidae

Subfamily: Crambinae

Bleszynski described C. zacconius in 1970, based on specimens from Senegal, Mali, Ivory Coast and Nigeria. According to Breniere

(1969), Risbec (1950) and Descamps (1956b) presented information on this species under the name Proceras africana (of authors, not Auriv.).

Appert (1952) also used the combination Proceras africana when he cited this species as an important pest of rice in the Senegal River

Valley. Breniere himself, based on correspondance from Bleszynski, listed the species as Chilo sp. (zacconius) Blesz. Nickel, in

Breniere (1969), considered the combination Parerupa africana (Auriv.) as the same as Proceras africana Auriv., as did Grist and Lever

(1969). However, Breniere (1969) suggested that in fact, the complex could involve three distinct species, Proceras africana Auriv., Chilo zacconius Bleszynski and Parerupa africana (of authors not Auriv.).

Bleszynski (1965, 1969) has detailed most of the taxonomical treatments regarding the subfamily Crambinae. Other treatments of the subfamily Crambinae have been made by Kapur (1950, 1967), and a critical review of the most important economic species within the subfamily has been made by Jepson (1954). The economic species important 84 on rice crops are treated by Grist and Lever(1969). A world revision of the genus Chilo was published by Bleszynski (1970).

Identification:

Bleszynski (1970) listed 41 species in his revision of the genus

Chilo, 18 of which are found in the Ethiopian region. He suggested

that the region is the present center of distribution of the genus.

Bleszynski also listed the species C. zacconius Bleszynski and C.

diffusilensis (S.de Joannis) = (C. phaesoma Martin) as occurring in

Senegal. The latter species was treated by Martin (1958) and its

distribution appears to be more confined to the wetter zone of Sene-

gal (Casamance), although, both species overlap in their distribution

(Bleszynski 1970).

The description of male and female genitalia of C. zacconius is

given in Bleszynski (1970). The description of the stages of the in-

sect is given in Risbec (1950) Appert (1952) and Descamps(1956b)

under the name of Proceras africana Auriv. and in Breniere (1969)

under the name of Chilo sp. (zacconius) Blesz.

Bleszynski (1969, p.12) offers the following description of the

genus Chilo:

Ocelli in most species well developed. Chaetosemata moderate. Labial palpi correct, often very long. Face variable, rounded or more or less produced forward, often with a distinct corneous point; sometimes with a triangular or rounded ridge underneath (formed by the clypeus). Fore- wing with free or coincident with Sc, R2 free, R3 and R stalked; R5 free, M1 free, M2 present stalked with Cul. 4 Forewing with pattern often much reduced, transverse lines present or absent; often with metallic shiny scales, singly or in patches. Colors mainly yellow and brown. Hindwing with no pattern, always lighter than forewing. Females always larger than males, and often with more pointed apex 85

and more oblique termen of the forewing. Male genitalia: uncus and gnathos proportionately shortand stout; tegmen with no lobes; juxta-plate often with long arms; saccus present; vinculum very narrow; pseudosaccuswell developed; sacculus not differentiated; costa only rarely with a process; the aedoeagus mostly slender,often with an arm from near base ventrally. Female genitalia: papillae anales broad, not differentiated; 8th tergite simple, linked to ostium pouch by a weak membrane; ostium pouch rather slightly differentiated, often not well demarcated from ductus bursae; the latter often lightly scleritized, long; bursa copulatrix often with one or two signa or scobina- tions.

The larva is about 13 mm in length and is striped longitudinally with five bands, one median and four lateral, "une mediane et4 lat-

erales; les plus extremes au-dessus des stigmates sontincompltes"

(Risbec 1950, p.142). The pupae is about 10 mm in length and can be

found in or outside the host plant (Breniere 1969).

The egg size is about 0.8 x 0.5 mm. The chorion surface is

sculptured with irregularly shaped polygones (Descamps 1956b). The

eggs are laid in batches of ten to 50 or more onthe leaves of the

host. The keys of Chilo species are in Bleszynski(1970).

Distribution:

Bleszynski (1970) and Breniere (1969) reported the following dis-

tribution of C. zacconius: Mali, Senegal, Nigeria, Ivory Coast,

Dahomey and Cameroun. The insect is also recorded in Sierra Leone

(Morgan 1973). Appert (1952) and Breniere (1969) reported the insect

in the Senegal River Valley.

Hosts:

According to Breniere (1969), the hosts of C. zacconius include:

cultivated rice, Oryza barthii (wild rice), Echinochloa stagnina,and

Sorghum arundinaceum. Bleszynski (1970) indicated that the genus Chilo 86 is known to be notorious pests of rice, sugar cane,maize, sorghum and other Graminae.

Damage:

The information available on C. zacconius suggeststhat the insect behaves like many other stem borersof rice, particularly of the genus Chilo. Appert (1952) reported that three to four larvae are often found in infested rice. They tunnel in the rice stem, result-

ing in the weakening of the plant and causing it tobreak-off in the wind. Appert concluded that C. zacconius is the most damagingrice

pest in the Senegal River Valley. Descamps (1956b) indicated that

tunnelling of the rice plant results in the production of emptyrice

panicles. Breniere (1969) and Vercambre (1975) reported that larvae

of C. zacconius cause two kinds of damage: attack on young rice seed-

lings during their vegetative growth may kill the growingpoints of

the rice plant, causing "dead heart", or the larvaeattack the rice

plant during the flowering stage, causing the formationof empty rice

panicles, giving the characteristic of a "white head". According to

Vercambre (1975), the two kinds of damage correspond to thedevelop-

ment of two generations of the insect. The first kind of damage

("dead heart") is caused by larvae of the first generation, and the

second ("white head") is caused by larvae of the second generationin

Senegal. The above types of damage are assumed to develop whenthe

rice crop matures in 100 days (from transplanting toharvest).

Grist and Lever (1969) reported that in some rice borers(e.g.

Tryporyza incertulas (Walker), every unit percent increasein damage 87 results in a loss of 13.27 pounds/acre. Kok and Varghese (1966) found in Malaysia that a borer infestation in rice of onelarva/two tillers, resulted in a 38% and 31% loss on 50 and 65 dayold plants, respectively. They concluded that the amount of loss depended on the intensity of infestation and on the age of the plantwhen infestation occurred. Generally, damage from rice stem borer is most severe during the ear stage of the riceplant (Grist and Lever 1969).

Methods of population and damage assessment of stem borers onrice or on other Graminae, have beenreported by Jepson (1954), Ishikura

(1967), Israel and Abraham (1967) and Metcalfe (1969).

Biology:

Little is known about the biology of C. zacconius. Appert

(1952) reported the following observations. The insect is active at

night. The eggs are deposited on the hosts (rice) leaves. Upon

hatching, larvae tunnel into the stems of the hosts. The species

Procera africana survive the dry season in the larval stagewhich re-

mains in the dead stem of the host. Pupation occurs at the beginning

of the rainy season and lasts eight to nine days. Appert (1952)

further noted that damage from the insect begins in early Augustin

Richard Toll, Senegal. Descamps (1956b) reported in Cameroun, that

the egg stage of Proceras africana lasted four daysand the pupal

period lasted six days during the rainy season. Breniere (1969) re-

ported that the pupal period of C. zacconius lasted five to sixdays

in Dahomey. Vercambre (1975) and I.S.R.A. (1975) reported that in

an insectary, C. zacconius developedin 30-45 days in Casamance, 88

Senegal. The female lays an average of 280 eggs. The adult sex ratio favors the male (2/3 males - 1/3 females). The egg incubation period lasts four days, and larval and pupal periods last 20-30 days and four to seven days, respectively. The insect develops four overlapp- ing generations from early July to October.

Breniere (1969) and Vercambre (1975) reported that there is no diapause in C. zacconius. They suggested that the insect survives the dry season in wild Graminae hosts, particularly in the more humid zones, or in off-season cultivated rice crops. Descamps (1956b) also reported that Proceras africana survives the dry season in Cameroun on Sorghum arundinaceum which grows in the wet zone or on thebank of the Benoue River in North Cameroun.

General accounts on the biology of most Chilo species (other than

C. zacconius) have been reported by Grist and Lever (1969), Grist

(1965), Kiritani and Iwao (1967) and Banerjee and Pramanick (1967).

Banerjee and Pramanick (1967) reviewed the life history of economic species of Chilo in the tropics. Their findings are summarized below to provide a camparison with C. zacconius. None of the species

summarized below are reported in either Senegal, Mali or the Senegal

River Valley.

1. Chilo suppressalis (Walker): this species is considered the most

damaging of the Chilo complex to rice in Southeast Asia. The fe-

male has an undiscriminate egg laying habit and up to 300 eggs are

laid in several batches. Incubation period lasts one to two days

or four to ten days, depending on the weather. The newly hatched 89

larvae immediately bore into the plant tissue. They disperse

into neighboring stems as they grow older and the plants whither.

The larvae can also be transported to other plants by the wind.

They are positively phototropic for a short period, then become

negative phototropic, until pupation. The "dead heart" charac-

teristic of damage is produced by the first generation larvae,

and the second generation larvae produce the damage whichresults

in "white head". Five to eight larval instars develop, but gen-

erally six are observed. The larval period lasts about five to

ten days. Adults live for four to eight days. The dry season is

passed in rice stubble below the soil as mature larva (India) or

the moth may survive throughout the year (Philippines).

2. Chilo partellus (Swinhoe): this species is considered more of a

pest on sorghum and maize than on rice. In Africa, the species is

reported in many of the Eastern and Central African countries.

The female lays its eggs on various parts of the host during a one

to three day period. The eggs are deposited in several clusters,

and a maximum of 300 eggs per individual female are deposited. The

incubation period of eggs is variable, depending on the season.

The newly hatched larvae first wander on the plant surface,feeding

on the leaf epidermis and then bore into the stemof the host, kill-

ing the central shoot. Adults live two to four days. The complete

life cycle takes 29-33 days in the summer and 83-210 days in the

winter, and six to seven generations occur per year (India).

Fukaya (1967) reported that for C. suppressalis, the lowest 90 threshold temperature for embryonic development is11-15°C., but the optimum temperature for egg development is 30-31°C. He indicated that larval duration differs in each generation and is associatedwith the physiological status of the host (rice) or the length of thephoto- period. The male larvae develop faster than female larvae,, but the situation is reversed in the pupae. The longevity of the adult depends on environmental conditions, mainly temperature. Adults live for two weeks at 15°C. but only four to five days at 35°C. He suggested that the moth has different ecotypes in Japan.

Control strategies:

Most of the control methods used against the Chilo-complex are reported from Southeast Asia. The symposium on rice stem borers held

at I.R.R.I. in 1964 (I.R.R.I. 1967) discussed many of themethods and a global assessment of the rice stem borers. The major methods of the

control of rice stem borers depends on the use of chemicals (Pathak

and Dyck 1973). Several factors influence the damage caused by rice

stem borers including: high rate of nitrogen fertilization, inten-

sive rice cultavation, planting density, morphological characteristics

of the rice plant, water management and soil reaction (Pathak 1972).

These characteristics are discussed under Maliarpha separatella

Ragonot. The following control methods pertain to several of the

better known Chilo species, but provides a framework for control of C.

zacconius.

Agronomical and mechanical control:

A general discussion of cultural methods used against rice stem 91 borers was given by Khan (1967), Grist (1965) andGrist and Lever

(1969).

Appert (1952) and Risbec (1950) recommended floodingof rice fields to control Proceras africana. Grist (1965) and Grist and

Lever (1969) reported the following techniques forcontrol of most rice stem borers: collection of the eggs in the seed bed'to prevent larvae from being dispersed to the field through hostplants. Cutting out infested plants before larvae start todisperse to adjacent plants.

Trapping larvae with rice straw or other gramineous stems,then destroying the larvae. Clean cultivation, close reaping of the rice plants to leave short stubble. Crop rotation, late transplanting of rice, flooding the rice field or completely submergingthe rice plant

for a short period, and stubble destruction or straw treatment.

Varietal resistance:

Several papers in the literature on rice stem borersdescribed varietal resistance of rice to borers (e.g. Israel 1967, Munakataand

Okamoto 1967, Pathak 1967a, 1972, Pathak et al. 1971, Athwaland

Pathak 1972, Khush and Beachel 1972).

It is generally accepted that rice varieties of the Japonica type

are less susceptible to rice stem borersthan are the Indica types.

However, this generalization does not always hold true at all stages

of plant growth (Pathak 1967a). According to Israel (1967), variation

in resistance is due to stage specificity, variation inthe structure

of the leaf sheath and stem at different stages of growth,effect of

borer incidence on tillering and/or the development ofsclerenchymatous 92

tissue in older plants. Munakata and Okamoto (1967 p.469) explained the differences in varietal susceptibility torice stem borers as:

"1) difference in oviposition preference amongadults, 2) difficulty of the hatching larvae in boring into rice stems,3) survival of larvae, 4) dispersion of larvaeand 5) compensatory activity of rice plants for injury". Athwal and Pathak (1972) and Pathak et al.(1971)

reported several structural characteristics ofthe rice plant which

could also contribute to the resistance. Pathak (1972) suggested that

tall rice varieties might be more attractive tomoths. He found that

susceptibility to the borer is positively correlatedwith the length

and width of the leaf blade.

Several rice varieties have been listed as resistantto rice stem

borers: Ptb28, TKM-6, EK1263 and Ptb21 (Athwal andPathak 1972,

Khush and Beachell 1972, Pathak et al. 1971). In Senegal, I.S.R.A.

(1975, 1976) reported that no resistance to stemborers has been ob-

served, although some varieties appear more susceptiblethan others

(e.g. Apura, Segadis, Ebandioulaye, Tunsart, TN1)and generally, the

group 0. glaberrima is the leastaffected by borers. I.R.A.T. (1971)

also indicated in Mali, that O. glaberrima is lessaffected by stem

borers than is O. sativa.

Biological control:

A large number of parasites and predators are known toaffect

the Chilo complex (Mickel 1967, Yasumatsu 1967,1975). Among these,

Trichogramma species are reported to give the greatest controlof the

complex, particularly when the stem borer population ishigh. 93

Breniere (1969) compiled the known parasites of C. zacconius and listed the parasites reported for Senegal and Mali as follows:

Euchalcidia soudanensis Stef. (Chalcidae), Tetrastichus procerae Risb.

(Eulophidae), Habrobracon sp. aff. triangularis Szepl., Perilitus sp,

Chelonus curvimaculatus Fer., Apanteles syleptae Fer. and Apanteles

procerae Risb. (Braconidae); Coelocentrus sp andCharops sp

(Icheumonidae); Pipunculus risbeci Seguy (Pipunculidae). The overall

rate of parasitism is reported to be 75% in the Senegal RiverValley

(Appert 1952). Descamps (1956b) reported that larvae parasitism is

25% in Northern Cameroun. Nickel (1967) indicated that the overall

rate of parasitism of the rice stem borer is variable, butgenerally,

there is a high rate of parasitism in Africa.

Chemical control:

Rao and Israel (1967) suggested that for chemical control of rice

stem borers, the insecticides should be directed againstadults during

their maximum abundance, the newly hatched larvae during their dis-

persing or migrating stage, or larvae and pupae inside leftoverstubble

and plant stalks.

Pathak (1967b) reported in experiments at I.R.R.I., that gamma

BHC was highly effective when mixed in irrigation water at a rateof

two to three kg/ha on plants 50 and 80 days aftertransplanting, re-

spectively. Pathak and Dyck (1973) suggested treatment of rice seed,

or placing the insecticide one inch below thesoil surface. These

methods resulted in the use of less insecticide than when applied

in the irrigation water. These methods also were least disruptive to 94

predators and parasites.

In Sierra Leone, Morgan (1973) foundthat foliar spray of 0.040 gamma BHC, EPN, Diazinon orCarbaryl (= sevin) applied at a rate of

300 gallons/ha effectively controlled rice stemborers. In Senegal, various experiments using Lindane + Urea,Diazinon, Chlorfenviphos and Carbofuran gave good control of stemborers (I.S.R.A. 1975, 1976). 95

Heliothis armigera (Hubner)

Noctua armigera Hubner 1805

Chloridea armigera (Hubner) Hampson 1903

Heliothis armigera (Hubner) Ochsenheimer 1826

Helicoverpa armigera (Hubner) Hardwick 1965

Synonyms

Heliothis pulverosa Walker 1857

Heliothis conferta Walker 1857

Heliothis uniformis Wallengren 1860

Chloridea obsoleta (Fabricius) Hampson 1903

Heliothis obsoleta (Fabricius) Turner 1920 [Common 1953] Leucania (Heliothis) obsoleta (F.) Risbec 1950

Common name: Old world boll worm

Order: Lepidoptera

Family: Noctuidae

Subfamily: Heliothidinae

Hardwick (1965) raised the genus Helicoverpa Hardwick andhe (1970,

p.18) stated, "The genus Helicoverpa has been raisedbecause they differ

sufficiently from dispacea (Linnaeus), type species ofHeliothis, and be-

cause no generic name is availablefor the group", in addition, he added,

"It was largely on the basis of character of the vesicathat corn earworm

and its relatives were recognized as constituting a naturalgeneric entity

descrete from Heliothis". In doing so, Hardwick (1965) recognized five

species groups within the genus, the Punctigera group(in Australia), the

Gelotopoeon group (South America), the Hawaiiensis group(Hawaii), the 96

Zea group (through-out the world) and the Armigera group (Old world).

Within the Armigera group, he recognized two species: Helicoverpa helenaeand Helicoverpa armigera. He divided the species Helicoverpa armigera (Hubner) into three subspecies: H. armigera commoni(Hardwick),

H. armigera conferta (Walker), and H. armigera armigera (Hubner). He reported that the Armigera group is distributed in Africa, Europe, Con- tinental Asia and Japan. Hardwick (1970, p.18) did not oppose recombin- ing the genera Heliothis and Helicoverpa if "larger generic units are deemed desirable", but he stated, "I'd strongly object however, to the submergence of Helicoverpa into Heliothis, when other more intimately groups are each recognized as genera on a much shallowerphylogenic level".

Singh (1971) rejected the genus Helicoverpa on the grounds that

it has no meaning for economic entomologists. He indicated (p.96) that,

"The Helicoverpa group species should be considered merely as a subgenus

or only a "section", a category which is little accepted by lepidopter-

ists" and he concluded,

The recognition of a subgenus Helicoverpa has no meaning at all for economic entomologists. In accordance with the rule of zoological nomenclature, the corn earworm should be named Heliothis armigera (Hubner). The name was widely used by 19th century entomologists, and was incorrectly replaced by Hampson at the beginning of the 20th century, and was restored in Western publica- tions in 1040.

Heliothis armigera (Hubner) has been reported among the pest complex of Graminae in Senegal by Risbec (1950) under the name of Leucania

(Heliothis) obsoleta F. In the Senegal River Valley, the insect is reported by Appert (1952) under the name of Heliothis armigera, and re-

cently, Appert (1976) treated Heliothis armigera among the pests of vegetables in Senegal. 97

Identification:

Historical notes on the nomenclature of Heliothis armigera

(Hubner) and related species are given by the followingauthors:

Common (1953), Pearson (1958), Todd (1955),Forbes (1954) and Hard- wick (1965, 1970). The authors indicated that there were many species involved in what was considered a single species(Heliothis armigera) and which was reported to occur throughout the world. Forbes (1954) distinguished the North American species from the complexand called it Heliothis obsoleta (Fabricius). From the same area (North America),

Todd (1955) found the species named by Forbes wasdescribed previously by Boddie under the name of Phaleana zea. He made the combination

Heliothis zea (Boddie) for what is now the corn earwormin North

America. Common (1953) found that four species wereinvolved in what was called Heliothis armigera inQueensland and he held the view that the species (Heliothis armigera) called by the same namein both North

America and elsewhere were different. Pearson (1958) suggested that any reference in the entomologicalliterature to Heliothis armigera

(Hb.) or H. obsoleta F. under the generic names of Heliothis or

Chloridea could be taken to refer to H. zea (Boddie) ifthey relate to the New world and H. armigera (Hb.)if it occurred in any other region, with caution in Australia. Hardwick (1965) worked out the taxonomy of the complex and foundthat many species or subspecies were

involved and may overlap in their distribution.

The morphological description of four Heliothis species,includ-

ing H. armigera is given by Kirkpatrick (1961a). He alsoprovided keys 98 to their immature stages. Hardwick (1965) published keys to the groups and to their species. H. armigera is also treated in Poitout

(1972), Delattre (1973), Rivany (1962), Schmutterer (1969), Appert

(1976), Risbec (1950) and Pearson (1958).

Pearson (1958, p.144) described the adult H. armigera. His description is summarized as follows: the adult length and wingspan are

18 mm and 40 mm respectively. The general color varies from dull yellow or olive-grey to brown with a darker brown markingwhich takes

the form of a distinct circular spot, half way between thebase and apex of the forewing; there is a smaller spot nearthe base and a

broad irregular band across the broadest part of the wing, parallel

to the first distal margin. The hind wing is pale with strongly

marked veins and a broad dark apical border with two lighter spots on

it. Kirkpatrick (1961a) illustrated the venation and markings of the

forewing and suggested that the hindwing color provided the most con-

sistent difference among the Heliothis species, whereas, forewing

markings were similar on all species.

The eggs are reported to be pale green when freshly deposited

and turn grey shortly after hatching; the egg size is about 0.477 x

0.528 mm (Hardwick 1965). The eggs are laid singly or scattered over

the host plant, but generally at the growing terminus of the host

(Hardwick 1965). Pearson (1958) noted that the shape of the egg is

spherical and its surface is sculptered by ribs.

The full grown larva is about 40 mm (Risbec 1950, Pearson 1958).

Pearson (1958, p. 144) reported that the larval color is variable and 99 the larval skin has a "characteristic granular appearance...the surface consisting of close set, minute tubercles". Kirkpatrick

(1961a,p.183) suggested that "the minute spinules" which cover the larval skin are a distinguishing feature of the genus Heliothis.

The larval body has longitudinal bands (Pearson 1958) which total five in number and are a distinguishing characteristic of H.armigera

(Risbec 1950, Appert 1976). The larvae are generally found in the fruiting bodies of the host (Hardwick 1965).

The pupae average 13.8 mm in length, "the length to posterior margin of fourth abdominal segment" (Hardwick 1965, p.105). The

dimension given by Risbec (1950) is 12-20 mm in length and 4.5 mm in

width. The pupae are generally found below ground at various depths:

5-10 cm (Rivnay 1962) and 2-3 cm (Lazarevic 1971), and appear tobe

related to the moisture content of the soil (Pearson 1958).

Distribution:

Hardwick (1965) reported that Helicoverpa armigera is distri-

buted nearly from the Pacific Islands westwards to the Canary Islands

of the West coast of Africa. He suggested that the moth is indigenous

to areas between 40 degrees south latitude and 40 degrees north

latitude. Schmutterer (1969), Rivnay (1962), Pearson (1958), Common

(1953) and Vishakantaiah (1972) listed H. armigera as broadly dis-

tributed in Africa (North and South), Southern Europe, the Near and

Middle East, India, Southern and Eastern Asia, Australia and New Zea-

land. The C.I.E. map 15(1968a) lists the countries where the moth

has been recorded. H. armigera is reported from the Senegal River 100

Valley by Appert (1952) and Breniere (1967), and Mallamaire(1956) listed the insect as distributed in Mali and Mauritania.

Hosts:

A large variety of plants are recorded as hostsfor H. armigera, and according to Singh (1971) more than 50 to 60 speciesof crops can

be listed as being damaged by H. armigera.

Among cultivated Graminae, H. armigera has been reported toin-

fest: Sorghum sp., Zea mays, Pennisetum sp., and Eleusine coracana

in East Africa (Lepelley 1959); Pannicum milliaceum(French millet),

Sorghum spp (grain sorghum), and Zea mays in Queensland(Kirkpatrick

1961b); Sorghum, Pennisetum typhoideum in India (Vishakantaiah1972);

"Mil" (Pennistum and Sorghum spp), and rice and maize in Senegal or

West Africa (Risbec 1950, Appert 1952, Risbec andMallamaire 1949).

H. armigera is a well known pest of cotton and most studies on

the moth are centered on that particular plant. Other botanical

families recorded as hosts of H. armigera (besides Graminae and Mal-

vaceae) include: Aizoaceae, Caryophillaceae, Compositae, Cruciferae,

Iridaceae, Leguminosae, Linaceae, Musaceae, Rosaceae, Rutaceae,

Solanaceae, Vitaceae, Euphorbiaceae, Amaranthaceae, Portulaceae,

Convolvulaceae, Chenopodiaceae, Cucurbitaceae, Capparidaceae and

Labiatae (Pearson 1958, Kirkpatrick 1961b).

Damage:

Damage studies of H. armigera have been reported mainly in re-

ference to cotton. Pearson (1958) gave a thorough treatment on the

subject and reported factors which cause the moth to become a severe 101

pest on cotton. He reported that larvae of H. armigera usually con- fine themselves to the reproductive organs of cottonand appear to favor consumption of buds and small bolls. Lazarevic (1971) reported that cotton damage reached 40% when thelarval population reached 0.83 to 6.58 larvae/row 3 m long.

Hardwick (1965) reported that the pest prefersmaize among its host plants and noted that generally the larvaefeed on the flowers and fruits of their host plants. Reed (1965h) and Appert (1967) reported that larvae of H. armigera feed on silks(maize) and may burrow down to feed on the cobs. Larvae can attack sorghum plants dur-

ing any of its growth stages but are mainlyimportant pests of the

flower head and developing grains (Anonymous1974). Larvae of H.

armigera feed on the sorghum head when it first appearsabove the

leaf sheath, but feeding decreases as the grainsharden (Anonymous

1974). This characteristic was also reported by Risbec(1950).

However, Vishakantaiah (1972) reported that thelarvae feed on the

hardening grain of Pennisetum typhoideum. Risbec and Mallamaire

(1949) reported that larvae of H. armigera feed onfoliage of young

rice seedlings. Young and Teetes (1977) listed H. armigera among

the "head" caterpillars of sorghum. They also found that larvae may

feed on the soft grains of sorghum, but they concludedthat H. armigera

tends to infest legumes and cotton more thancereal crops.

Passlow (1973) indicated that control of H. armigera onsorghum

is economically sound only if the sorghum ishigh yielding, or is

cultivated under irrigation and only when two orthree larvae 102

"2 cm or more long" are observed/sorghum head. In the U.S.A., studies of the related species, H. zea (Boddie) showedthat 16 larvae/sorghum head reduced the yield by 25 to 30% (Burkhardtand Breithaupt 1955).

Buckley and Burkhardt (1962) found, when larvaeof H. zea were caged on three varieties of sorghum at adensity of one to 13 larvae/sorghum head, the yield was reduced 6-48%. They found that 75% of the damage was done by the last two instars. Kinzer and Hendersen (1968) also found that 20 H. zea larvae/ten sorghum heads was aneconomically damaging population.

Biology:

The adult H. armigera is active mainly at night or atdusk (Appert

1976, Pearson 1958). Both sexes live an average of 11 days, up to a maximum of one month (Reed 1965a). Lazarevic (1971) found adult longevity lasted between three and eight days at temperaturesof 25-30°C.

Length of the adult period is reported to vary,depending on the nature of larval food (Hardwick 1965), or availability of nectar orits equivalent as food for the adult (Pearson 1958). The preoviposition period has been reported to last two to five days(Poitout 1972). Coaker

(1959) reported that the oviposition period lasted 10.4days, and

Rivnay (1962) suggested that it lasted two to threeweeks.

The female lays eggs on various portions of thehost plant, but

prefers the growing terminus of the plant (Hardwick1965). Coaker

(1959) and Roome (1975b) suggested that ovipositionof the moth follows

the flowering cycle of the host plant. The average number of eggs

laid/female may range from 12 to 1248, with an average of373.8 at

25-30°C. (Lazerevic 1971), or from 0 to 3065 according toReed (1965a). 103

Hardwick (1965) recorded a maximum of 4394eggs/female. The incubation period of eggs may last three days at 22°C. to nine days at

17°C. (Rivnay 1962). Kirkpatrick (1962) found that egg incubation required three to four days at 28°C. andfive to six days at 18°C.

The number of larval instars and theirdevelopmental rate vary with temperature, kind of diet and strainof population. Poitout and Cayrol (1969) found in laboratorypopulations, that five to six larval instars and occasionally seven tonine may develop. They reported that the occurrence of five larvalinstars was related to the vigor of the population and wasfavored at a temperature range of

25-35°C. Less than 40% of the larvae passedthrough five instars if natural food such as bean or tomato wereused, regardless of the

individually temperature. Hardwick (1965) found among 239 larvae,

reared to adult, that 69% developed sixlarval instars, 30% developed

five instars, and one developed sevenlarval instars. Singh (1972)

found that 10% of the population developed sevenlarval instars on

cabbage in the laboratory. Coaker (1959) found that larvae of H.

armigera developed in 21.8 days on maizeand in 33.6 days on sun-

flower corolla and receptacle.Hardwick (1965) found at a constant

temperature of 25°C., that the larvalperiod lasted an average of

15.4 days. Lazarevic (1971) reported that larvalperiod lasted an

average of 25 days. Six larval instars appear to be the most common-

ly recorded (Reed 1965a, Hill 1975, Meng etal. 1962).

The young larvae commonly feed on theepidermal layer of small

leaves (Hardwick 1965). On sorghum, the larvae begin feeding on 104 young flowers and later on developing grains (Roome 1975b). On legmun- inous plants, the larvae may feed on the tender leaves and subsequently bore into the pods and the developing seeds (Lall 1964). The mature larvae leave the host plant and burrow into the soil where pupation occurs (Pearson 1958, Hardwick 1965, Risbec 1950). Reed (1965a) reported that pupation can also occur in maize cobs.

The prepupal period lasts less than three days according to Hard- wick (1965), three to four days according to Rivnay (1962) and one day at 25°C. according to Lazarevic (1971). The length of the pupal stage varies, depending on the temperature, kind of host plant and the presence or absence of diapause. Coaker (1959) found that the pupal period of H. armigera lasted 19.7 days after larvae had fed on three week old maize cobs, and 26 days when fed on seven week old cotton bolls. Hardwick (1965) found that the mean pupal period lasted 13.2 days. Lazarevic (1971) found the duration of pupal stage in nondiapausing larvae lasted between 23 and 116 days. He reported that in field or laboratory populations, the percentage of diapausing larvae did not exceed 9%. He added that regardless of the season, some pupae remain in diapause and the percentage of pupae in the population increased during the dry period or when irrigation was stopped

(in the Gezira and Sennar of Sudan). Risbec (1950) reported that the pupal period lasted ten to 19 days during the rainy season and about

13 days during September-October in Senegal, but is longer later in the season.

The complete duration of the life cycle of H. armigera and the 105 number of generations the moth can produce each year are variable through the geographical distribution of the insect. Lazarevic (1971) found that the life cycle was completed in 31-41 days at 25-30°C. on cotton leaves in the laboratory. He reported that H. armigera developed three complete generations from early October to mid-January in cotton fields in Gezira (Sudan). In the mediteranean area, the moth developed two to four generations each year (Poitout 1972). In China,

Meng et al. (1962) reported that three generations/year are observed north of 40°N latitude, four between 32 and 40°N, five between 25 and

30°N, six to the south of 25°N latitude and seven generations may occur each year in some locations. Hardwick (1965) found that the genus (Helicoverpa) remained active throughout the year intropical regions with the exception of those that entered a drought induced diapause.

Control strategies:

Pearson (1958) reviewed the control of H. armigera in cotton growing areas of Africa. Hardwick (1965) discussed the control methods used against the corn earworm complex. The factors which make

H. armigera a major or a potential pest have been reported as follows:

1. Migration of the moth can explain the wide distribution of the in-

sect (Hardwick 1965) and may allow infestations to occur in new

or isolated crops (Appert 1976).

2. A wide host range of plants not botanically related provide food

material for the moth during the whole year.

3. The facultive diapause which exists, allows the moth to survive 106

in areas of low rainfall. Schmutterer (1969) indicated that in

the Sudan, H. armigera survives through the dry season as dia-

pausing pupae. In addition, nondiapausing individuals continue

laying eggs on wild hosts or on cultivated crops under irrigation.

Schmutterer (1969), Lazarevic (1971) and Pearson (1958) noted that

in the Sudan, the weed Ipomea cordofona (Convolvulaceae) is the

most important host for the moths survival during the dry season.

4. In addition to the above characteristics, the high fecundityof

the moth and the confinement of larvae in the fruiting structures

of the host plant, lead Hardwick (1965) to suggest that control

should be aimed at protecting specific crops rather than stabil-

izing the populations as a whole.

Agronomical and mechanical control:

Control techniques used against the corn earworm complex have been reported by Hardwick (1965) as follows: manipulation of planting date and crop rotation, to avoid periods of maximum attractiveness for oviposition; hand picking larvae from maize ears and clipping or pulling silk from the tip of maize ears. Rivnay (1962) suggested controlling weeding to avoid larval migration from adjacent fields. Ploughing the ground to destroy pupae has also been reported to give some degree of control.

In the Sudan, during the dry season, cultivation of someplants

(e.g. Hibiscus spp.) is prohibited, but this method is of little value (Schmutterer 1969). Some plants appear to be preferred for oviposition (e.g. maize and Dolichos lablab) and are suggested for use 107 as trap crops (Reed1965b, Pearson 1958).

Varietal resistance:

Some authors have observed differencesin the infestation rate of H. armigera in several sorghum types,but no resistance has been

reported. Dogget (1964) reported that morelarvae of H. armigera were found on sorghum withclosed panicles than on sorghum with open

or erected heads. He suggested that natural mortalityof larvae in

the closed head type sorghum probablyaccounted for these differences.

Breniere (1970) also indicated in Senegal,that closed panicle type

sorghums are more infested by "earhead" pestsin general than the

open panicle sorghums. Nonveiller (1969) made similar observations

in Cameroun, and found strong correlationsbetween infestations of

"earhead" lepidopterous pests (e.g. Eublemma gayneriRoths; Noctuidae)

and the structure of sorghum panicles. He suggested theuse of this

criteria for sorghum selection andbreeding.

Resistance studies on the similar species,H. zea (Boddie) are

reported by Painter (1951) and recently inthe review of Maxwell et al.

infestation of H. (1972). Buckley and Burkhardt (1962) observed that

zea on tight sorghum headsis generally more severe than in the open

type sorghum. Maxwell et al. (1972) reported that severalresearchers

have observed that soil fertility, nitrogenbalance in corn plants,

feeding deterrents, feeding inhibitors,growth inhibitors, and nutri-

tional value of diet influence the damageby H. zea.

Biological control:

H. armigera has many predators andparasites. Rao (1968) listed 108 the parasites recorded on various Heliothis species in India. Pearson

(1958) compiled the parasites of H. armigera reported in Continental

Africa. He reported that mass release of Trigromma luteum (egg parasite) in South Africa did not control the insect. Roome (1975a) and Roome and Daoust (1976) found in Botswana, that a local unpurified virus (NPV) was effective as a standard control to prevent loss in sorghum heads from H. armigera. They indicated that the virus was as effective as carbaryl in reducing yield loss.

Risbec (1960) reported the following parasites of H. armigera found in Senegal: Braconidae: Disophrys nigricornis BR., Apanteles ruficrus Hal., Apanteles maculitarsis Cam.; Eulophidae: Euplectrus laphygmae Ferriere; Tachinidae: Sturmia inconspicua Meig., Sturmia laxa Burm.

Chemical control:

In Madras (India), DDT in a 10% dust or 0.2% spray are suggested to protect sorghum against H. armigera (Nagaraja and Abraham 1959).

Passlow (1959) suggested that paper bags dipped completely or partially in an emulsion containing 0.5% Aldrin and put over sorghum heads gave some control of H. armigera in breeding plots. Passlow

(1973) and Anonymous (1974) recommended Endosulfan at 730 g or Car- baryl at 1.1 kg a.i./ha for control of H. armigera in sorghum fields when two to three larvae were found/head of sorghum (in Queensland).

Appert (1967) recommended 10% DDT dust at 1.5 kg a.i./ha for control of H. armigera in maize. In vegetable crops, he (1976) recommended using Endosulfan, Demethoate or baits using DDT or 109

Carbaryl (in Senegal). Singh and Singh (1972) found that Carbaryl applied at 0.8 kg/ha gave good control of H. armigera in tomato.

Carbaryl has a half life of 0.52 days and there was no detectable residue in tomatoes ten days following the spray. 110

Maliarpha separatella Ragonot

Maliarpha separatella Ragonot 1888

Synonyms

Anerastia pallidicosta Hampson 1896

Ampycodes pallidicosta Hampson (Hampson in Ragonot 1901)

Rhinaphe pallidicosta Hampson 1918

Enosima vectiferella Ragonot 1901

Rhinaphe vectiferella Ragonot (Hampson) 1918 [Martin 1958, Breniere et al. 1962, Kapur 1967]

Common name: Madagascar white rice borer

Order: Lepidoptera

Family: Pyralidae

Subfamily: Phycitinae (Kapur 1967)

Maliarpha separatella is reported to be an important pest of rice crops. Kapur (1967) stated that this species is widely distributed in the Paleotropic (Ethiopian and Oriental) regions, but it has been reported on rice only in parts of Africa. Martin (1958), who is considered the first to have clarified the taxonomy of M. separatella, stated that specimens from Senegal were reared from rice. Breniere et al.(1962) reported that this species has been known from Madagas- car since 1901 and they considered M. separatella as the most important rice stem borer in that area. They suggested that M. separatella is a native of Continental Africa, but the economic status of the insect is uncertain on that continent.

Appert (1964) listed the species as infesting rice crops in Sene- gal. Breniere (1969) and Schmitz (1969) recorded M. separatella in 111 the Senegal River Valley, particularly in Richard Toll, andthey pointed out the potentiality of the insect becoming a major pestof rice grown under irrigation.

Identification:

The taxonomy of M. separatella Ragonot is treated inMartin (1958).

He illustrated and described the genitalia. Kapur (1967) developed

keys to the most important noctuid and pyralid stem borers. He provided diagnoses of families, subfamilies, genera and species ofthe

important pests. Breniere et al. (1962) described and illustrated all

stages of M. separatella and a description of M.separatella is also

given by Appert (1967, 1970, 1964, 1963), Nye (1960), and Gristand

Lever (1969).

Adult length is reported to attain 12 mm in the male and 15 mm

in the female (length from head to the tip of wings)(Breniere et al.

1962). Grist and Lever (1969, p.108) stated that "the forewings in

males[are]brownish ochreous with darker markings in females, the fore-

wings[are]whitish yellow to yellowish orange with a single fuscous

discal spot". In male adults, the antenna is longer (7.25 mm), where-

as in the female the length is 6.85 mm(Breniere et al. 1962). Kapur

(1967, p.9) reported that the genus Maliarpha is distinguished by

"fore and hind wings with vein 4 (or M3) absent, i.e. only 3 veins

arise from median nervure; proboscis weak".

The mature larvae was described by Grist and Lever (1969, p.108)

whitish yellow in color, brown pronotum with darker anchor-like abdominal segments; females with grooves 112

on the eighth and ninth segments, the latterbeing short; length 18 mm.

Nye (1960, p.31) noted that in mature larvae, "the head is medium brown; prothoracic shield pale yellow brown, body creamy white; pinnacula very pale; and the caudal plate is pale yellowish brown". He reported the size of full grown larvae as 24 mm in length and 3 mm in breadth.

The pupa is elongated and brown "brune allongee" with cremaster bearing three pairs of straight spines. A dot "tache" which is pink in color is observed around the fifth abdominal segment in male pupa

(Breniere et al. 1962, Appert 1967).

The egg size is 0.6 0.7 mm in length and 0.4 - 0.5 mm in width.

The eggs are seedlike and yellow when freshly laid and turn to brown at the time of hatching (Breniere et al. 1962). They are deposited in masses and are protected in a case made from the glue that the female spreads on the leaf before ovipositing; this glue makes the leaf wrinkle and thus forms the case.

Distribution:

The distribution of M. separatella falls in the Paleotropic

(Ethiopian and Oriental regions) (Kapur 1967). Within the Ethiopian region, the insect has been recorded in: Madagascar, Mali, Kenya,

Sierra Leone, Senegal, Ghana, Niger, Upper Volta, Cameroun, Tanzania,

Malawi, Uganda, Swaziland, Ivory Coast, Nigeria, South African Repub- lic, Sudan, Zambia and Chad (C.I.E. map 271, 1970).

Hosts:

The hosts of M. separatella are indicated to belong almost 113

exclusively to the genus Oryza (wild and cultivated rice) (Nye 1960,

Harris 1962, Ingram 1958, Martin 1958, Breniere 1969, Appert 1967).

Hill (1975) stated that the insect was also found on Echinochloa

holubii in Swaziland. I.R.A.T. (1971) also reported that M. separa-

tella infests Echinochloa stagina in Mali.

Damage:

The damage caused by M. separatella is similar to that done by

other rice stem borers (Grist and Lever 1969). The larvae tunnel in

the rice stems and feed on the internal tissue, which may cause the

plant to lodge or prevent formation of normal rice panicles. Nye

(1960) indicated that infested rice plants may have either panicles

which are normal or unfilled panicles which are white. Appert (1967)

stated that environmental conditions may lead to preventing rice pan-

icle formation or can induce lodging of the plant which makes it diffi-

cult to diagnose the damage characteristics of M. separatella.

The severity of infestation from M. separatella is variable.

Where only a single rice crop is annually produced, the damage is not

serious (Nye 1960), but where there is a continuous rice cropping and

a long wet season, such as in parts of Madagascar, infestation of80%

is recorded (Breniere 1969). Grist and Lever (1969) reported that

observations have found for every 1% of rice stems attacked by M.

separatella, there is an annual loss in yield of 24.8 kg/ha. Schmitz

(1969) noted 7-8% infestation on experimental plots in Richard Toll

(Senegal). He suggested that the insect could be expected to become

more serious where two crops of rice are raised annually. 114

Biology:

Maliarpha separatella has been thoroughly studied in Madagascar.

Breniere et al. (1962), Breniere and Rodriguez (1963), Breniere and

Lacoste (1962), Appert (1967, 1970) reported the biology and control of the insect in that area. Pathak (1968) and Grist and Lever (1969) also reported elements of biology and control of M. separatella.

Breniere (1969) reviewed the insect with references to West Africa.

According to Breniere et al. (1962), adults of M. separatella are positively phototropic. They are mainly active at night and during the day they can be found mostly in the lower portions of rice plants. The adult longevity may last about five to six days or longer, but never exceeds 12 days (Appert 1970). Oviposition starts two days following adult emergence (Appert 1967), or it can take up to four or five days in an unmated female (Breniere et al. 1962). The female lays eggs for two to three days, and the number of eggs per individual female can reach 200-300 (Appert 1967). The eggs are laid in masses on the upper surface of leaves (Breniere et al. 1962).

The egg incubation is variable, depending on temperatures, and may require seven to 12 days (Breniere et al. 1962, Appert 1967). Upon hatching, the young larvae migrate to the tip of the plant where they remain for a short period. Some larvae may suspend themselves with a silken thread and can be dispersed to surrounding rice plants by the wind. Others may fall into the water and are able to swim due to air layer surrounding their bodies. The larvae which remain on the tip 115 of the plant, migrate towards the base of theplant and crawl between the leaf sheath and stem and finally into the stem(Breniere et al.

1962, Appert 1967, Pathak 1968). Breniere et al. (1962) indicated that six to seven larval instars develop. Their developmental period is variable, depending on temperature, stageand condition of the host and absence or presence of larval dormancy. The larval period lasts one to two months. The authors observed in Madagascar, that larval dormancy developed in areas experiencing dry seasons orin areas with a single rice crop per year. No resting stage is found

in wet zones or where rice cultivation is continuous.

The full-grown larvae have a tendancy to feed on thebasal parts

of the plant where pupation also occurs. The pupal stage last nine

to 15 days at 28°C. and 70% relative humidity(Breniere et al. 1962).

The complete life cycle of M. separatella requires42-90 days in

Madagascar (Breniere et al. 1962). From the same area, Appert (1970)

indicated that three generations of the insect occur a yearand breed-

ing is continuous in the wet zones of the islandswhich affords con-

tinuous rice cropping. Vercambre (1975) suggested that M. separatella

may develop three generations in Senegal; twoduring the rainy season

and one in the dry season (mostly in larval dormancy).

Control strategies:

Control of rice stem borers are indicated by various authors to

involve similar techniques. The differences found generally involve

the phenology of the specific pest and can vary withgeographical

area, but more often, are tied to the croppingschemes. The control 116 techniques of M. separatella have been reported from Madagascar (e.g.

Breniere et al. 1962, Breniere and Lacoste 1962, Breniere and Rodri- quez 1963, Appert 1967, 1970). Khan (1967), Pathak (1968) and Pathak and Dyck (1973), Tandon (1973) and Grist and Lever (1969) also reported population dynamics and control measures for rice stem borers.

The control strategies are summarized as follows:

1. For many rice stem borers, it is generally admitted that inten-

sive cultivation and high rates of fertilization increases the in-

cidence of rice pests. Mehta (in Tandon 1973) advocated at least

20-30 g of technical pesticide should be used for every kg of

fertilizer mix. Pathak (1968) stated that rice fields receiving

high rates of fertilization and rice plants containing high levels

of nitrogen are generally found more suitable for larval growth.

2. Plant spacing, tillering potential of the rice variety, and mor-

phophysiological characteristics of the rice plant influence ovi-

position of rice stem borers (Pathak 1968). These characteristics

were shown to influence damage caused by Maliarpha separatella

(Appert 1970).

3 Soil texture and fertility are important factors reported to in-

fluence rice stem borers incidence. Khan (1967) noted that severe

damage occurred in clay soil than in sandy soil and rice grown in

water logged and saline areas were more susceptible to borer attack.

4. Where rice is grown continuously, it is recognized that later crops

suffer heavier infestation than do early ones. 117

Agronomical and mechanical control:

The review by Khan (1967) mentioned various methodsof controlling rice stem borers, though a number of them areconsidered either to involve high energy expenditure or areof limited value. Among the measures which the author reported were: floodingthe rice stubble together with dragging; destroying the stubble by eitheruprooting and plowing followed by exposure to the sun, androoting the stubble by chemical means (e.g. calcium cyanide). All these methods are aimed at larval destruction, because generally larvae areconfined to the stubble after rice harvest. Shifting the date of sowing or crop rotation can also minimize the borer incidence. Khan (1967) also indicated that broadcast crops suffered less damage to rice stemborers

than transplanted ones, although the latter is known toyield more.

Varietal resistance:

Pathak (1968) stated that tall rice varieties with long wide

leaves and larger stems are susceptible to rice stemborers. In Mad-

agascar, some differences on susceptibility toM. separatella has

been found in rice varieties. Appert (1970) found less oviposition

by the insect on the variety Indica 342 than on Japonica1300 and

1572. He also suggested that IRAM 1345, which is an upland rice var-

iety, suffered less damage from M. separatella.

The International Institute of Tropical Agriculture , Ibadan,

Nigeria: I.I.T.A. (1973) found the rice varietiesSikasso, W1263, and

Taitung 16 had low levels of damage from M. separatellaand Sesamia

calamistis. I.R.A.T. (1971) reported that the local rice 118

(Oryza glaberrima) in Mali, was found to be less infestedby M. separatella and other borers than Oryza sativa. The report indicated that infestation was found to reach 40-80% in the lattervariety, whereas, 5-10% was the percentage rate of infestation onOryza glaberrima. I.S.R.A. (1976) also reported that Oryza glaberrima offersgood levels of resistance to many stem borers.

Biological control:

A list of parasites recorded on M. separatella wasgiven by

Breniere et al. (1962), Breniere (1965, 1969). The following parasites are reported from Senegal and Mali:Phanerotoma saussurei Kohl (Bracon-

idae); Bracon sp. (Braconidae); and Goniozus sp.(Bethylidae) all from

Senegal, and Phanerotoma sp. (Braconidae), and Goniozus sp.(Bethylidae)

from Mali. All are reported to be larval parasites (Breniere 1969).

There are also several parasites recorded from Ghana, Swaziland, Sierra

Leone and Madagascar. I.R.A.T. (1973b) reported that Goniozus procerae

(Bethylidae) is an important parasite of rice stem borers in Casamance

(Senegal. The report stated that parasitism of larvae can reach

10-30% in May-June and December-January.

Chemical control:

Pathak and Dyck (1973) suggested that up to 10% "dead hearts"

caused by stem borers within the maximum tillering stage of therice

plants do not cause significant loss in yield, providing the cropis

protected later. They suggested that either root-soaking treatment

of rice seedlings before transplanting or placing the insecticide one

inch below the soil surface near the roots of recently transplanted 119

seedlings would provide good control against rice stem borers. They noted that the root-soaking treatment can be made from 1000 ppm in-

secticide and should be done 12-24 hours before transplanting.

Appert (1970, 1971a) suggested that when more than seven egg masses of M. separatella are found per two square meters, control is necessary. He recommended application of gamma BHC (granules) in

irrigation water at 3 kg a.i./ha. The treatment was made 40 days

after transplanting the rice plants or 10 days prior to the end of

the tillering period. Where rice cropping is continuous, the author

suggested the use of Diazinon at the same rate. The first rice crop

is treated 50 days following transplanting with a second application

30 days later. The second rice crop is treated with one application of Diazinon 40 days after transplanting the crop (the recommendations are made for Madagascar).

I.R.A.T. (1971) indicated that more than one ton yield difference was observed between treated and untreated plots of rice using Urea

+ Lindane (gamma BHC). It stated that Lindane granules applied at

2 kg a.i./ha seven and 50 days after rice planting is recommended for control of the rice stem borer and diopsids (Diptera) in Casamance

(Senegal). 120

Sesamia calamistis Hampson

Sesamia calamistis Hampson 1910

Sesamia vuteria Stoll, Hampson (ex errore) 1910

Sesamia mediastriga Bethune-Baker 1911 (Tams and Bowden 1953)

Common name: Pink Borer

Order: Lepidoptera

Family: Noctuidae

Subfamily: Amphypirinae

Sesamia sp. are recognized as important pests of Graminae (Tams

and Bowden 1953, Rao and Nagaraja 1969), and in Africa, S. calamistis

Hampson, S. cretica Lederer, and S. botanephaga Tams and Bowden are

listed among the most serious pests of cultivated Graminae (Appert

1963, 1964, Schmutterer 1969, Tams and Bowden 1953). The distribution

of the species and their economic status in the cultivated Graminae

are variable. S. calamistis is reported to be an important pest of

maize and sugar cane and to some extent, sorghum and rice (Tams and

Bowden 1953, Rao and Nagaraja 1969). It is also the most common

species in dry areas (Jepson 1954, Usua 1968a,b,). S. cretica is

listed as a serious pest of sorghum, but is confined to the Mediter-

annean area (Northeast Africa, North Africa), Sudan,Middle East,

and Southern Europe (Rivnay 1962, Tams and Bowden 1953, Schmutterer

1969). S. botanephaga is injurious to maize and to some cultivated

sorghum, rice and sugar cane, and is confined to wet zones (Tams and

Bowden 1953). 121

The above three species of Sesamia are recordedin Senegal.

Risbec(1950) listed S. vuteria (= S. calamistis) in the pestcomplex of cultivated Graminae. Appert (1952) and Schmitz (1969) recorded S. cretica as an injurious pest of Graminae in theSenegal River Valley.

Breniere (1967) listed S. botanephaga as a pest oncultivated sorghum and Pennisetum species in Bambey (Senegal), andhe (1969) listed S. calamistis as a pest of rice in the Senegal RiverValley, though he indicated that S. calamistis was more frequent inupland rice than in irrigated rice.

Identification:

The morphological description of 15 species and twosubspecies of

Sesamia are given by Tams and Bowden (1953). They also provided keys to species of Sesamia and to manyother noctuid genera economically important to cultivated Graminae. They reported that S. calamistis is variable in both color and size. Usua (1969) provided a key based on chaetotaxy for separating larvae of S. calamistis, S.penneseti and

S. botanephaga. Williams (1953) described the immature stages of S.

calamistis, and Nye (1960) and Tams and Bowden (1953)illustrated the

adult genitalia. Tams and Bowden (1953), Ingram (1958) and Harris

(1962) suggested that the only positive method ofdistinguishing the

species is by examining the male and female genitalia(see Caresche

and Breniere 1962).

Adults: the forewings are pale cartridge buff and the hindwings

are white. The general color of the adult moth varies fromlight to

dark buff with ochraceous to fuscous overtones. The wing span varies 122 from 22 to 30 mm in the male and from 24 to 36 mmin the female (Tams and Bowden 1953).

The larva is 2 mm long when newly hatched andreaches 25 to 30 mm when fully grown. The head is medium brown, prothoracic shieldpale yellow-brown, and the buff colored body is diffusedwith pale pink

dorsally. Pinnacula are seldom visible. The caudal plate is yellow-

brown. The sides and underside of the body are tingedwith yellow

(Moutia 1934, Williams 1953, Nye 1960).

The pupa is 17 to 20 mm long and about 4 mm wide. The head is

dark reddish-brown and the thorax and abdomen arereddish-brown dorsa-

lly and yellow-brown ventrally. The pupa is generally found in a

cocoon made of debris cementedtogether with silk threads (Williams

1953, Walters 1974).

The eggs are round, flattened with fluted sides. They are cream

color and measure 0.7 mm in length (Moutia 1934). There are few

crenulation in the chorion (Harris 1962).

Distribution:

Tams and Bowden (1953), Nye (1960), Appert(1967), and Grist and

Lever (1969) gave the following distribution: Angola, Cameroun, Congo,

Gambia, Ghana, Kenya, Nigeria, Malawi, Mali, Senegal, SouthAfrica,

Ivory Coast, Sudan, Tanzania, Uganda, Zambia, Islandsof Zanzibar,

Madagascar, Reunion, and Mauritius. Nye (1960) found the moth at all

altitudes, from sea level to 8,000 feet in East Africa, andnoted that

the insect tends to be limited to the hills, lake sides, riversand

irrigated areas. Jepson (1954) indicated that the species is most 123 common on savannah areas wherethere is a pronounced dry season.

Hosts:

The known host plants of S. calamistis belong almostexclusively to the family Cramineae. The cultivated gramineous plants that S. calamistis is reported to attack include: Sorghum vulgare, Pennisetum typhoides (millet), Oryza sativa (rice), Zea mays(mais, corn),

Triticum spp. (wheat), Saccharum officinarum(sugar cane), and Eleusine coracana (Finger millet). Other hosts include: Beckeropsis uniseta,

Cenchrus echinatus, Coix lachryma-jobi, Cyperusdistans, Hyparrhenia rufa, Lolium sp., Panicum maximum, Paspalidum paniculatum,Paspalum conjugatum, P. urvillei, Phalaris arundinacea, Pennisetum purpureum,

Rottboellia compressa, R. exaltata, Setaria barbata, Setariasplendida,

Sorghum arundinaceum, S. verticilliflorum, Tripsacumlaxum, Veticeria zizaniodes, Vossia cuspidata, (compiled by Rao and Nagaraja1969).

Breniere (1969) found the moth on rice in the SenegalRiver Valley and indicated that the species is more frequent in rainfedrice.

Damage:

The larvae are essentially borers of young shoots,but in corn all parts of the plant may be fed upon with exceptionof the roots

(Appert 1971b). The larvae will attack and tunnel into the main stem

of the host shortly after hatching and thereafterseldom leave the

protection of the stem, except when migrating(Harris 1962). Feeding

is mainly internal in the stem of the host causingmechanical damage

by severing the vascular bundles (Nye 1960, Harris1962, Walters 1974).

The intensity and consequences of infestation aredependent on 124

the host. Rao and Nagaraja (1969) indicated that sugar cane is able

to compensate to some extent for the loss of shoots by producing new

shoots or by increased growth of remaining shoots. Harris (1962)

stated that for corn, adequate compensation for loss of stand is not

high enough because the corn does not tiller. Reports from the winter

rainfall areas of South Africa, indicate for sweet corn, reduction in

stand up to 10% is common and infestation ratios of 30 to 70% damaged

plant stems and 30 to 40% damaged cobs are regularly encountered

(Walters 1974). Harris (1962) indicated in Nigeria, that the development of a single larva reduced the yielding capacity of the stem by

28% of the mean dry cob of healthy stems.

Biology:

The life history and bionomics of S. calamistis has been reported

by Ingram (1958), Nye (1960), Harris (1962), Appert (1964, 1967, 1971b),

Usua (1968a,b, 1970a) and Pointel (1967). Walters (1974) provided

a review of the status of this species as a pest of gramineous crops

in South Africa, and Rao and Nagaraja (1969) discussed the Sesamia

species complex as pests of sugar cane. Earlier accounts of the life

history and bionomics of S. calamistis published under the name of S. vuteria Stoll were given by Moutia (1934) and Risbec (1950).

The adults are nocturnal and stay hidden among plants and plant

debris during the day which is a general characteristic of noctuid moths. They emerge from pupa in the late evening (Harris 1962) and

live two to 14 days (Walters 1974). In Uganda, under laboratory con-

ditions, the male dies within 24 hours and the female lives 72 to 96 125

hours (Ingram 1958).

The eggs are laid during the three or four nights following the night of emergence (Harris 1962) in clusters of two to three rows between the leaf sheath and stem of the host plant on the inner surface of the leaf sheath (Ingram 1958). The number of eggs per cluster varies considerably, ranging from about 10 to 75 (Rao and Nagaraja

1969) up to 100 or more (Harris 1962, Walters 1974). A single female lays an average of 300 eggs (Harris 1962, Ingram 1958), with a maximum of 540 eggs reported from species in Nigeria (Harris 1962) and

327 in Uganda (Ingram 1958). Walters (1974) indicated that temperature and host plant species utilized by the larvae influence egg production. He noted that females produced an average of 477 and 242 eggs when the larvae were reared on sweet corn and elephant grass, respectively. The optimum temperature for egg production is 21-26.5°C.

(Walters 1974).

The young larva tunnel directly into the stems of the host plant shortly after hatching (Harris 1960, Nye 1960, Ingram 1958). The time spent before tunneling in the stem is the critical period for successful control (York 1967), because the larvae are protected in the stem (Harris 1962). The number of larval instars and the total time required to complete larval development depends largely on the temperature and the type of host plant (Walters 1974). Rao and

Nagaraja (1969) reported that there was an average of seven or eight larval instars. In South Africa, at a constant temperature of 10°C. seven instars are produced which may take 200 days to develop; whereas 126 at 26.5%C., six instars develop in 21 days. From the same area, S. calamistis required an average of 22 days to complete larval development when fed sweet corn, but 35 days when fed on elephant grass. In

Sorghum alum, ten larval instars may develop (Walters 1974). Ingram

(1958) indicated that it required 27 to 36 days for larvae to develop in the laboratory in Uganda.

The prepupal period of S. calamistis lasted one day and the pupal period was ten to 12 days in Uganda (Ingram 1958). Nye (1960) found that the pupal period lasted about two weeks. Harris (1962) reported that the pupal period lasted seven to 13 days in Samaru (Nigeria).

Walters (1974) reported that it required one to two days for the prepupal stage and ten to 20 days for the pupal period, at temperatures of 21-26.5°C., respectively.

Pupation takes place in the host plant (Harris 1962, Appert 1967) in a cocoon made of pieces of leaves. In Finger millet, the cocoon is constructed in the leaf axil (Ingram 1958), and in corn, the pupae can be found either inside the stems or in the feeding tunnels in the cob

(Walters 1974). The total life cycle is 45 to 58 days (Ingram 1958).

In Nigeria, it required 43 to 70 days with the development of eggs and pupae required six to seven and seven to 13 days, respectively (Harris

1962). Appert (1967) indicated that six to eight weeks were required for completion of the life cycle in Madagascar.

Vercambre (1975) stated that under insectary conditions, S. calamistis completed its life cycle in 50 to 70 days; the egg stage 127 required four to seven days, larvae 35 to 45 days and pupae nine to

14 days. He stated that in Senegal, the insect occurs primarily towards the end of the rainy season on cultivated Graminae. There is no resting stage in the life cycle of this species and several over- lapping generations are produced throughout the year (Harris 1962,

Ingram 1958, Appert 1969, Walters 1974). Usua (1968a) concluded that

S. calamistis is well adapted for drier zones.

Southwood (1969) in his study of population of insects attacking

sugar cane, found that S. calamistis has a maximum natality rate(Rm) of 58, a generation time (Tc) of 66 days, a potential rate of increase

(rp) of 0.062, and a potential finite rate of increase (antilog rp) of 1.064. The methods of computing these parameters of population

growth are given in Southwood (1966, 1969).

Control strategies:

Rao and Nagaraja (1969) reviewed the control methods used against

S. calamistis attacking sugar cane. Walters (1974) reported that in

South Africa, several methods of control are used for limiting infest-

ations of S. calamistis in corn. Olufade (1974) indicated the diff-

erent means of control established over the years in Nigeria against

this pest on corn. Appert (1967, 1971b), Harris (1962), Ingram (1958),

Nye (1960), Grist and Lever (1969) summarized several different

aspects of S. calamistis control.

Walters (1974, p.5) indicated that to control S. calamistis

successfully on gramineous crops in general, and sweet corn in parti-

cular, one should observe the following factors: 128

the insects are present and will attack the plants during the greater part of the year; the insect can attack plants at any time during the growing stage; larvae could migrate at any time from alternative host plants to attack the cultivated plants; the young larvae bore directly into the stems and cob of maize on hatching; the larvae are particularly destructive during the seedling stage, and for corn, the best results are obtained and the least spray material wasted when the spray is directed directly into the stems and cob of sweet corn.

Agronomical and mechanical control:

Regular destruction of all crop residue, volunteer plants, and all gramineous plants which might be alternative host plants in and around the area to be cultivated at the beginning of the growing season are recommended (Rao and Nagaraja 1969, Walters 1974). When hand weeding is practiced, the weeds should be burned or buried to destroy the eggs or larvae they harbor (Rao and Nagaraja 1969). Usua, in

Olufade (1974) noted that the mortality rate in stem borer larvae is higher if maize stems are cut and left laying in the ground, than if stems are left standing in the ground. Appert (1971b) advocated clean cultivation, adequate nutrient supply to the crop and ploughing and burning of dry stalks to reduce the population of S. calamistis.

Varietal resistance:

I.I.T.A. (1973) found that some maize lines showed some degree of resistance to S. calamistis under field conditions. It was also indicated that the rice varieties, Sikasso, W1263 and Taitung 16 had a low incidence of "dead heart" from infestation of S. calamistis and

Maliarpha separatella. I.I.T.A. suggested that resistance to S. calamistis may involve both biochemical and biophysical factors. 129

Breniere (1973) provided an account of the I.R.A.T. program inrefer- ence to varietal resistance to major insect pestsin "French West

African" countries. Breniere (1971) indicated that the improvement of plant varieties is hindered by the fact that varieties most resis-

tant to borers are usually less productive than thesusceptible ones.

Harris (1962) reported that the thin stemmed dwarf varieties ofGuinea corn (Sorghum vulgare), derived from NorthAmerican sorghum, are more

susceptible to damage than the thick stemmed local varieties.

Biological control:

A great number of parasite species reared from S. calamistisand

from other species of the genus Sesamia have been reported in the

literature. Ingram (1958), Risbec (1960), Harris (1962), Breniere

(1965), Appert (1964) and Jerath (1968) listed the parasites reared

from S. calamistis.

In Senegal and Mali, the following parasites of S. calamistis

have been reported by Risbec (1950, 1960) and Appert (1964):

Braconidae: Phanerotoma sp., Phanerotoma major Brues, Apenteles

ruficrus Hal (Senegal), Apanteles sp. (Mali); Chalcididae: Brachymeria

sesamiae Gahan (Mali); Eulophidae: Pleurotropis furvum Gahan, Tetra-

stichus sesamiae Risbec (Senegal); Pteromalidae: Plactecrizotes

sudanensis Ferriere (Mali). Risbec (1960) reported that 20% of S.

calamistis larvae were parasitized by Apanteles sp.

Appert (1971a) indicated that Apanteles sesamiae Cam introduced

in Mauritania and Reunion, controlled up to 60% of S. calamistis in

these islands, although, the same parasite failed to control 130

S. calamistis in Madagascar. Ingram (1958) stated that in Uganda, S. calamistis is controlled by Apenteles sesamiaeand another unidentifed

Braconidae species.

Chemical control:

Ingram (1960) was unable to obtain yield increaseand only partially controlled S. calamistis on sorghum, evenwith weekly application of insecticide. DDT, Dieldrin, Endrin, Ryana and Cryolitehave been reported to increase yield in maize(Rao and Nagaraja 1969).

Caresche (1962) and Caresche and Breniere (1962)recommended spraying with Endrin for control of S. calamistis on sugar cane. On irrigated

rice, Appert (1967) recommendedTrichlorfon in Madagascar. Grist and

Lever (1969) indicated that spray treatment withE.P.N., Endrin or

Diazinon reduced S. calamistis on rice. 131

Spodoptera exempta (Walker)

Agrotis exempta Walker 1856

Laphygma exempta (Walker) Hampson 1909

Spodoptera exempta (Walker) Zimmerman 1958

Synonyms

Prodenia ingloria Walker 1858 [Zimmerman 1958 and Brown and Dewhurst 1975] Common name: African Army worm

Order: Lepidoptera

Family: Noctuidae

Subfamily: Amphypirinae

Brown (1965) and Brown and Dewhurst (1975) listed most economic

Spodoptera species which are found in Africa. Brown (1962) reviewed

Spodoptera exempta and found that this species is the most important

pest of cultivated Graminae among the Spodoptera species. Risbec

(1950) and Appert (1957) listed the species under the name Laphygma

exempta (Walker) and found the insect among the pest complex of cul-

tivated Graminae in Senegal and Mali. Appert (1952) found the insect

in the Senegal River Valley and reported that the damage was sporadic.

Vayssiere and Galland (1950) reported that the insect has been found

damaging rice crops in Kayo (Mali). Breniere (1967) also listed

Spodoptera exigua (Hubner) among the pest complex of cultivated sor-

ghum and Pennisetum spp in the Senegal River Valley (Richard Toll).

Identification:

Zimmerman (1958) provided the taxonomy of,the Hawaiian species of 132

Spodoptera and keys to distinguish the species. The taxonomy of the genus Spodoptera is also treated byBrown and Dewhurst (1975). They described eight species of the genus known to occurin Africa and the

Near East and provided keys to the different stagesof the species.

They suggested that the keys developed by Zimmerman(1958) were not

reliable when applied to separate the African Spodopteraspecies.

They insist on the form of mandibles, particularly in separatinglarvae

of S. exempta from those of S. exigua. Blair (1974) worked out keys

to separate larvae of five species of Spodopterawhich included both

S. exempta and S. exigua. The description of the stages of S. exempta

are also found in Risbec (1950) and Appert(1967). The review of

Brown (1962) listed various authors who have previouslydescribed the

stage of the moth.

Brown and Dewhurst (1975, p.233) gave the following characteris-

tics of all Spodoptera moths,

(a) all imagines are of medium size, with wing span ranging from 24-43 mm; (b) forewing vary from pale greyish to brown to dark greyish brown, orbicular andreniform spots usually well defined; (c) hind wings alwayswhite (except in Spodoptera malagasy (Viette), hind wing veins may or may not be infuscate.

Adult S. exempta (Walker) is reported to attain 13 mm inbody len-

gth and to exhibit a wing span of 30 mm (Risbec 1950). Brown and Dew-

hurst (1975) stated that the wing span is usually about 29-32 mm.

They noted that the male has a grey coating and the female has black

inner hair scales at the tip of the abdomen which are usefuldiagnostic

characteristics. Whellan (1954) reported that males are brightly

variegated and females are concolorous. 133

The full grown larva attains 30 to 40 mm inlength. Its general color is black and its head is blackish andreticulate. Several longitudinal greenish yellow lines and a mid-lateral line runalong the body (Appert 1967, Hill 1975). There is larval polymorphism which affect both color and activity of larvae (Faure 1943,Matthee 1946,

Whellan 1954, Brown and Dewhurst 1975). Whellan reported that one form of larvae is called "solitarious" or "passive". It prevailing color is green and inconspicuous and the larvae arequiet in habit.

He called the second form "gregarious" or "active". This form is distinguished by its black and conspicuous color andvigorous habits.

The polymorphism is brought about when larvae areforced to group together in close proximity. According to Brown (1962) the polymorphism, unlike that found in locust species, is solely under theinfluence of

external conditions which force the larvae to grouptogether. Brown and Dewhurst (1975) indicated that the form "gregaria" arisesfrom

about the third instar onwards. They also provided keys to separate

the two larval forms.

The pupa is brown or black and about 17 mm in length (Hill1975).

It is enclosed in a cocoon generally found in moistground (Whellan

1954). The pupal characteristics used in keying Spodoptera species

are given in Brown and Dewhurst (1975).

The eggs are pale yellow when freshly laid; they turnblack prior

to hatching and are covered by hair sclaes from thefemale abdomen

(Brown and Dewhurst 1975). 134

Distribution:

S. exempta (Walker) is widely distributed (Zimmerman 1958, Brown

1962, Risbec 1950). The moth occurs world wide except for North and

South America. The C.I.E. map A53 (1972) lists the distribution

range of the moth. Brown and Dewhurst (1975) listed the following

African states which fall into the moth distribution: Egypt, Senegal,

Gambia, Mali, Niger, Sudan, Guinea, Sierra Leone, Ghana, Nigeria,

Cameroun, Gabon, Zaire, Ruwanda, Burundi, Ethiopia, Eritrea, Somali

Republic, Kenya, Uganda, Tanzania, Angola, Zambia, Rhodesia, Malawi,

Mozambique, Southwest Africa, Botswana, Swatziland, Lesotho, South

Africa and Islands of the Atlantic and Indian oceans.

Hosts:

A long list of host plants is recorded for Spodoptera exempta, and includes both graminaceous and nongraminaceous plants. Brown

(1962) and Brown and Dewhurst (1975) compiled the following list of plant hosts: Cultivated Graminae: Avena sativa (oats), Eleusine coracana (Finger millet), Hordeum vulgare (barley), Oryza sativa

(rice), Saccharum officinarum (sugar cane), Secale cereale (Rye),

Sorghum spp (millet, Kaffir corn), Triticum vulgare (wheat), Zea mays

(maize), Pennisetum typhoides (Bulrush, Pearl millet), Eragrostis tef, and Panicum miliaceum.

Among the noncultivated Graminae, various grass species are listed. Other botanical families listed include: Compositae, Convolvul- aceae, Cyperaceae, Iridaceae, Leguminosae, Liliaceae, Malvaceae,

Musaceae, Rubiaceae, Solanaceae, Polygonaceae, Amaranthaceae, 135

Ficoidaceae and Zygophyllaceae. Brown (1965) found that 36 species of Graminae and four Cyperaceae were commonly infestedby S. exempta in East Africa. He concluded that despite the variety of hosts recorded for the moth, S. exempta is confined to twofamilies: Graminae and Cyperaceae.

Damage:

Larvae of S. exempta feed on foliage of the hostplant and the host may be completely skeletonized, particularly on youngseedlings

(Brown 1962). Appert (1967) stated that dryland rice could suffer heavy damage from larvae if rice plants are not above20 cm in height

at time of infestation. Risbec and Mallamaire (1949) also reported

that larvae may cause heavy damage on rice and otherGraminae seed-

lings. Swaine (1954) noted that sorghum is able to recoverfrom

heavy infestation beyond one month growth stage,provided there is

adequate moisture, while rice and maize are unable to recover. Carn-

ejie (1974) reported that sugar cane crops can recoverfrom infestation

of S. exempta because the growing point of the plantis seldom affect-

ed. Anonymous (1974) stated that larvae are often found inthe throats

of the host plants (e.g. sorghum) before head emergenceand that dam-

aged plants have a ragged appearance.

Several studies report on damage simulation of Army worms.

Davidson (1965), Wardlaw, Carter and Anderson(1965) reported on arti-

fical defoliation of wheat and found 20-28% loss in yieldif the de-

foliation occurred after heading and up to about sevendays after

flowering. Four to ten percent loss in yield resulted ifdefoliation 136 occurred from the seedling stage (up to five leaf stage)until heading begins; 13-17% loss in yield occurred when plants inthe seedling stage were cut at ground level. Brown and Odiyo (1968) found that damage caused by S. exempta larvae increased during the latterhalf of larval growth but damage was negligible except at high larvaldensity. They noted that less than two larvae can destroy all theleaf area of maize plants at the six to seven leaf stage, but at a higherdensity the plants can be eaten right down to the ground stems, resulting in a50% crop loss if the plant survives. Brown and Mohamed (1972) found from simulated damage and crop loss in maize and sorghum that regen- eration of maize and sorghum can be complete when defoliation occurs at early stage. Methods for estimating the areas of leaves destroyed by chewing insects is given by Benjamin, Freeman and Brown(1968).

Biology:

Brown (1962) has reviewed the literature pertaining to S. exempta.

Biology of the moth has also been reported by Appert (1967), Fonseca

Ferrao and Santos (1965), David et al. (1975), Brown and Dewhurst

(1975). The larval polymorphism has been studied by Faure (1943)

and Matthee (1946), and their findings are summarized in Brown (1962).

Adult moths are reported to be mainly active at night and are

physiologically capable of flying continuously throughout the night

(Aidley 1974). The females have a strong tendancy to fly following

emergence (Brown and Swaine 1966, Brown,Betts and Rainey1969, Brown

1970). Fonseca Ferrao and Santos (1965) found that adult longevity

is 6.72 days (greenhouse), and Whellan (1954) indicated that 137 oviposition may start two days following adult emergence. The review of Brown (1962) reported that oviposition may start two to four days after emergence, and sometimes longer (except for parthenogeneric eggs), depending on the temperature.

The eggs are deposited in batches generally on the lower surface of leaves, but may also be laid outside the host (Brown and Dew- hurst 1975). Eggs may be deposited at various heights on the plant, and up to seven feet on maize plants (Whellan 1954). The number of eggs laid by the individual female can reach up to 602 (David et al.

1975) or 10-300 (Hill 1975). The incubation period is variable, depending on the temperature (Brown 1962) and can last 174 hours at

20°C. or 74 hours at 25°C. (David et al. 1975).

Upon hatching, the first instar larvae stay in groups and are active mainly in the day time.After the third larval stage, feeding activity is confined to the night(C.Agr. Pr. Pays chauds 1968a).

Brown and Odiyo (1968) and Fonseca Ferrao and Santos (1965) reported six larval instars. David et al. (1975) obtained five to six larval instars in the laboratory. Vayssiere and Galland (1950) reported that larval development can take from 15 days to a month, and according to Brown (1970), the period lasts two to three weeks. David et al.

(1975) observed that the larval period takes 12-16 days at 25°C. and

25-30 days at 20°C. The larval polymorphism observed to occur (Faure

1943, Matthee 1946) results from external conditions which cause larvae to stay in groups at close proximity which induces differences in behavior and the developmental rate in larvae (Brown 1962). 138

Whellan (1954) stated that the "passive" or "solitarious" larvae are

slower in developmental rate as compared to the "active" or "gregar-

ious" larvae and may be found at a density of seven to 14 larvae per square foot without being a threat. Rose (1975) reported that the adult population may differ in quality in that small adults produce mainly females which do not migrate and produce "passive" larvae.

The mature larvae pupate indiscriminately on patches of de-

caying grass, at the bases of stems, under clods or stones (Hattingh

in Brown 1962) or in soil which is moist (Whellan 1954). The pupal period is reported to last five days in July (Risbec 1950), seven days

at temperatures of 26°C. (Appert 1967), 18-19 days at 20°C. or 10-12 days at 25°C. (David et al. 1975).

The complete duration of the life cycle of S. exempta is variable.

Fonseca Ferrao and Santos (1965) reported that it can average 26.3

days in the greenhouse (May) and six generations may be produced a

year. They also noted in the field (Angola) that the moth may have

four generations per year. They reported larval diapause in Angola,

but Brown, Betts and Rainey (1969) found no diapause in the life his-

tory of S. exempta, either in the laboratory or field in East Africa.

Control strategies:

Various authors recognize that outbreaks of S. exempta are sudden

(Brown 1962). This recognition led to several studies of the moth in

East Africa and resulted in establishing weekly forecasts of the prob-

ability of larval infestations (Betts et al. 1970, Odiyo 1970, Aidley

1974, Betts 1975). These studies also revealed the following: 139

1. Adults are able to sustain long flights and migrate over long dis-

tances following their emergence. Reproductive activity and ovi-

position may be delayed until the moths have reached considerable

distance from the emergence site. The displacement of the moth is

associated with weather, in that it occurs in relation to the dis-

placement of the Intertropical Convergence Zone (I.T.C.Z.) which

brings rains in different areas at different times. The overall

result is to bring concentrations of the moths to areas that have

seasonal rains (Brown and Swaine 1966, Brown, Betts and Rainey

1969, Rose and Law 1976, Blair and Catling 1974, Betts 1975).

2. There are seldom outbreaks of consecutive generations of the moth

in infested areas because the moth generally leaves the area be-

fore breeding takes place (Brown and Swaine 1966, Brown 1962,

1970).

3. Even though S. exempta feeds on a great number of host plants, it

is confined to Graminae and Cyperaceae, except when these two

botanical families are lacking (Brown 1965, 1970, Appert 1967).

4. The damage caused by the larvae depends on the stage and the kind

of host plant (Brown and Mohamed 1972), density and stage of the

larvae (Brown and Odiyo 1968), and forms of larvae (Whellan 1954,

Brown 1962).

5. The natural hosts of S. exempta are wild grasses (Graminae) and

the movement of larvae onto cultivated crops results from inedible

or lack of natural hosts (grasses) (Brown 1962, C. Agr. Pr. Pays

Chauds 1968a). 140

Agronomical and mechanical control:

Brown (1962) compiled various methods to control S. exempta,

particularly during periods of outbreak. The methods include shallow

ploughing in order to destroy larvae and pupae, hand picking and

crushing larvae, beating and sweeping larvae, burning larvae with a

flame thrower, trenching or establishing barriers in front of ad-

vancing larvae, flooding the field, rotating cultivated crops and

varying the time of planting. All of these methods are reported to

provide some degree of success, although Brown (1970) stated that

many of these techniques are of little value owing to the migratory

habit of the moth.

C. Agr. Pr. Pays Chauds (1968a) stressed that weed control is an

important component in controlling S. exempta and Army worms in gen-

eral. The report suggested eliminating weeds both within and outside

cultivated crops because the moth generally develops on wild grasses.

Brown (1970, 1972) suggested that weeding cultivated crops should be

done very early, otherwise it should not be done, to avoid larval

dispersal into cultivated crops.

Varietal resistance:

Differences in varietal susceptibility to S. exempta is indicated

to occur, but varietal resistance to the moth is poorly known.

Vayssiere and Galland (1950) reported that thick stemmed rice

varieties were preferred during a moth infestation which occurred in

Kayo, Mali. Brown (1962) reported that there is some degree of sus-

ceptibility to S. exempta among "sorghum millet". According 141

to Smee in Brown (1962), in Pennisetum sp some strains are preferred, and Fonseca Ferrao and Santos (1965) reported that first instar larvae failed to develop on Pennisetum purperum (elephant grass).

In North America (U.S.A.), some varietal resistance is indicated

to occur in a similar species, Spodoptera frugiperda (J.E. Smith).

Wiseman et al. (1966, 1967) found that corn appeared to be highly preferred by S. frugiperda over Tripsacum dactyloides (related species) by the first instar larvae. They stated that damage in the latter

species may result from nonpreference or the lack of an arrestant

rather than an antibiosis factor. They suggested that Tripsacum spp

germ plasm in corn could be beneficial, but resistance inthe seedling

stage (corn) may not be positively correlated with resistance in more

mature stages. Brett and Bastida (1963) found some resistance in

sweet corn to S. frugiperda, and suggested that the resistance was due

to plant vigor or tolerance. Larvae preferred succulent plant tissue

which was in good physical condition, but there was no distinction

between different varieties in any other regards. Leuk et al.(1968)

and Leuk (1970) reported resistance in some lines of millet ( Pennisetum

typhoidcs) to S. fruglperda which they explained by extreme nonprefer-

ence or antibiosis.

Biological control:

Brown (1970) stated that 56 species of parasites and eight hyper-

parasites of S. exempta are reported in East Africa and 19 species in

other African countries. He noted that parasitism ranges from three

to 25% in East Africa, but suggested that biological control of 142

Spodoptera exempta is not practical, although biological controlhas been achieved in Hawaii. An exhaustive list of parasites recorded on

S. exempta was reported by Brown (1962). Brown and Swaine (1965) reported a nuclear polyhedrosol virus found in pupa, prepupa and larva, except in the first instar, but Brown (1970) statedthat no more than

5% larval mortality from the virus has been found in thenatural population.

Risbec (1950) found a high degree of parasitism on S. exempta in

Senegal and Mali, and listed (1960) the following parasites: Tachinidae:

Tachina zanthapis (Senegal); Phoridae: Megaselia sp. (Senegal);

Icheumonidae: Pristomerus sp. (Senegal), Charops sp. (Senegal and Mali);

Braconidae: Apanteles syleptae Ferr. (Senegal and Mali); Eulophidae:

Euplectrus laphygmae Ferr. (Senegal).

Chemical control:

Swaine (1954) suggested prompt application of 10% DDT + 3% gamma

BHC to control S. exempta. In East Africa, DDT is used to control

S. exempta, although substitutes are considered (Yeates et al. 1971).

FonsecaFerrao and Santos (1965) indicated that Endosulfan is used

to control the moth in Angola. They reported that wheat plants were

not infested by the moth when soil was treated withAldrin one to two

months prior to attack.

C. Agr. Pr. Pays Chauds (1968a) recommended Endosulfanapplied at

a rate of one kg a.i./ha in the source ofinfestation and Carbaryl at

two kg a.i./ha in areas to be protected from Army worms. In addition,

the report suggested the use of 10% DDT dust at a rate of 10-20 kg/ha, 143

or baits containing Dieldrin and rice bran.

Brown and Odiyo (1969) suggested that for chemical control to be

effective, it should be done during the early stages of larval de- velopement (six to seven days after hatching). 144

Spodoptera littoralis (Boisduval)

Hadenia littoralis Boisduval 1833

Prodenia littoralis (Boisduval) Mabille 1879

Spodoptera littoralis (Boisduval) Viette 1963 (Viette 1963, Brown and Dewhurst 1975)

Common name: Egyptian Cotton worm

Order: Lepidoptera

Family: Noctuidae

Subfamily: Amphipyrinae

This moth had been known under the name Prodenia litura (Fabricius)

for many years. Viette (1963) found the name Prodenia litura (F.) in-

cluded two distinct species, one in the Oriental region and another in

Africa, the Middle East, Southern Europe, Madagascar and the adjacent

islands. He made the combination S. littoralis (Boisduval) for the

species originally described as occurring in "Bourbon" and Madagascar

and along the African coast, and Spodoptera litura (F.) for the species

distributed in the Oriental region.

Spodoptera littoralis is a well known pest, particularly in Egypt,

where the moth has been considered the most damaging insect on cotton

for many years (Willcbcks 1925, Maher and Rasmy 1969). The moth has

also been known in Senegal, Mali and Mauritania. Vayssiere (1925)

stated that the moth was frequently observed in Senegal and Mali, and

individuals of the moth were also found in southern Mauritania,

"Elle (Prodenia litura (F.) est assez frequente au Senegal et au

Soudan Francais, quelques individus ont ete rencontres dans le sud 145

Mauritanian" (Cit. after Risbec 1950, p.381). Appert (1952) listed

the moth among the insects of economic importance in the Senegal

River Valley, although the damage of the moth was sporadic. Recent-

ly, Breniere (1967) listed the moth among the pest complex of"Mil"

of Senegal, and observed the moth in the Senegal River Valley(Richard

Toll).

Identification:

The identities of S. littoralis (Boisduval) and S. litura

(Fabricius) have been confused up to 1963 (Viette 1963, Hafez and

Hassan 1970, Cayrol 1972, Brown and Dewhurst 1975). The taxonomy of

S. littoralis, along with the most important Spodoptera species were

recently reviewed by Brown and Dewhurst (1975) who also provided keys

to all stages of the moths. Blair (1974) provided keys to the larvae

of economically important species of Spodoptera. The different stages

of S. littoralis were also treated by Risbec (1950), Pearson (1958),

Buyckx (1962), Rivnay (1962), Appert (1967, 1976), Caresche et al.

(1969), Schmutterer (1969), Talhouk (1969) and Delattre (1973).

Adult S. littoralis have a body length of 15-20 mm (Rivnay 1962,

Appert 1976) with a wing span of about 30-41 mm (Brown and Dewhurst

1975). Its general body color is brownish grey (Rivnay 1962). The

forewing is strongly variegated with light and dark markings; the hind

wings are white with veins not or scarcely infuscate (Brown and Dew-

hurst 1975). Pearson (1958) reported that the forewings are brown

with pale lines along the veins and the bluish areas at their tip and

base distinguish the male from the female. The hind wings are pearly 146 white (Pearson 1958). Zaher and Moussa (1961) reported that morphometrics (length of the body, hind femur, costal and apical margins of the wings of forewing and cleavimum) of adults are greater in moths which develop from larvae reared in isolated conditions than those which are reared in crowded cultures.

The eggs are creamy white when freshly laid or pale metallic if they are infertile and turn to blue-black dorsally and pale below as the embryo develops (Brown and Dewhurst 1975). The eggs are laid in clusters and are covered with scales from the female body. The color of the scales is golden brown or buff and is a diagnostic characteristic for distinguishing eggs of S. littoralis from those of other

Spodoptera species. Pearson (1958) described the egg as spherical and slightly flat. The dimension of eggs may range from 1/3 mm (Risbec

1950) to 0.6 mm (Rivnay 1962). Delattre (1973) developed a table for identifying eggs of most Lepidoptera which infest cotton, including

S. littoralis.

The full grown larva is about 35-45 mm in length and its head width is 2.9 mm with some dorsal and dorso-lateral stripes running along the body and black spots above the spiracle of the last segment

(Brown and Dewhurst 1975). Color of the larva is green during early instars, but is brown, grey brown or black during later instars (Pear- son 1958, Appert 1976, Caresche et al. 1969), but never green(Brown and Dewhurst 1975). Zaher and Moussa (1961), Rivnay and Meisner

(1966) and Hodjat (1970) reported a larval polymorphism is brought about by crowding conditions and expressed in differences of color, 147 behavior, and developmental rates between crowded and isolated individual larvae.

The pupa is 16-20 mm in length and its cremaster bears one pair of terminal spines (Brown and Dewhurst 1975). The color of the pupa is brown or red-brown (Rivnay 1962, Risbec 1950). The pupa is generally found in moist soil at a depth of 3-4 cm (Appert 1967, Caresche

et al. 1969).

Distribution:

Spodoptera littoralis is reported to be cosmopolitan in distribution. The overall range of the moth distribution is given by the

C.I.E. map A232 (1967). Caresche et al. (1969) reported that this

species is normally confined to tropical and subtropical and warm

temperature regions, where the mean temperature does not fall below

10°C. They noted that the moth is distributed chiefly in areas be-

tween the latitudes 35°N and South and within the annual isothermof

20°C.

Brown and Dewhurst (1975) reported the following African states

which fall in the distribution area of S. littoralis: Morocco,

Algeria, Tunisia, Lybia, Egypt, Mauritania, Senegal, Gambia, Mali,

Niger, Chad, Sudan, Guinea, Sierra Leone, Liberia, Ivory Coast, Upper

Volta, Ghana, Togo, Nigeria, Cameroun, Central African Republic, Gabon,

Zaire, Rwanda, Burundi, Ethiopia, Eritrea, Somali Republic, Kenya,

Uganda, Tanzania, Angola, Rhodesia, Malawi, Mozambique, Southwest

Africa, Botswana, Swatziland and South Africa. The moth is also distri-

buted in the islands of the Indian Ocean (e.g. Madagascar) and in the 148

Atlantic Islands (e.g. Canary Islands).

Hosts:

Spodoptera littoralis is Polyphagous. Moussa, Zaher and Kotby

(1960) reported that 112 plants which are classified in 44botanical

families have been recorded as hosts of this species in various trop-

ical and temperate zones. They also indicated there is a choice

among the plants. They reported that in Egypt, where 73 plants are

listed as hosts of the moth, 16 are preferred for oviposition,45 for

feeding and 12 for feeding and ovipositing. Brown and Dewhurst (1975)

listed the families and the plant species recorded to be hosts of S.

littoralis. Their list included among the gramineous crops: Oryza

sativa, Saccharum officinarum, Sorghum vulgare and Zea mays. Among

other botanical families, the list included: Leguminosae (e.g.

Arachis hypogea, Acacia arabica, Phaseolus vulgaris, Vigna unguicul-

ata, Trifolium alexandrinum), Iridaceae, Labiatae, Lauraceae,Liliaceae,

(e.g. onion), Malvaceae (e.g. cotton, okra), Moraceae (e.g. figs),

Musaceae (e.g. banana), Myrtaceae (e.g. Guava), Nyctaginaceae, Palmae

(e.g. date palm), Phytolaccaceae, Pinaceae, Piperaceae, Pontederiaceae,

Polygonaceae, Portulacaceae, Punicaceae, Ranunculaceae, Rhamnaceae,

Rosaceae, Rubiaceae, Rutaceae (e.g. orange), Salicaceae, Scrophular-

iaceae, Solanaceae (e.g. tomato), Sterculiaceae, Theaceae,Tiliaceae,

Umbelliferae, Verbenaceae, Violaceae, Vitaceae, Amaranthaceae,

Araceae, Cactaceae, Caryophyllaceae, Casuarinaceae, Chenopodiaceae,

Compositae, Coniferae, Convolvulaceae (e.g. sweet potato), Cruciferae,

Cucurbitaceae, Cupressaceae, Dilleniaceae, Euphorbiaceae (e.g.cassava). 149

Caresche et al. (1969) stated that among the recordedhosts of

S. littoralis, the plants which are preferredfall into (decreasing

preference) Leguminosae, Solanaceae, Malvaceae, Moraceae,Compositae,

Graminae, Chenopodiaceae and Cruciferae.

Damage:

Damage to plants by S. littoralis is affectedby larvae which

essentially feed on the foliage, although other partsof the host

plant may also be attacked. Caresche et al. (1969) reported that

buds and flowers of cotton occasionally may bedamaged. Appert (1967)

reported that leaves of maize may be stripped andthe plant completely

skeletonized. In addition, the stem may be tunneled andripening

grains fed upon by the larvae. Grist and Lever (1969) indicated the

larvae cause serious injury to rice plantsand cut the panicles,

particularly if the larvae occur in large numbers. On leguminous

plants, the larvae feed on the foliage and onripening pods in the

soil (e.g. ground nut), whereas, on tomato or cottonthe larvae may

tunnel into the fruit (Schmutterer 1969, Rivnay1962, Caresche et al.

1969).

The pest status of S. littoralis is reported to bevariable

within its distribution range. Pearson (1958) and Schmutterer (1969)

reported that the moth is an occasional pest oflucerne, peas and

onions in the Sudan. Cayrol (1972) reported that the moth is a major

pest of tomato and vegetables in Morocco and Algeria. In Egypt, S.

littoralis is reported to be a major pest, particularly on cotton,

legumes and maize (Maher and Rasmy 1969, Willcocks1925). 150

Dulong (1971) stated that this species causes severe damage on cassava in Madagascar. In Senegal, Risbec (1950) observed the moth severely damaging ground nut and cowpea "niebe". According to Appert (1952) this species is a sporadic pest in the Senegal River Valley.

In areas where S. littoralis occurs, but remains a minor or occasional pest, the population is suppressed by the sub-optimal relative humidity which prevails in the area (Talhouk 1969) and high temperatures (Schmutterer 1969). The attraction of the moth into riverain cultivation (Rivnay 1962) and/or into irrigated areas(Cayrol

1972) underline the potential of the moth in becoming a major pest in areas introducing irrigation as a component of their cropping schemes.

Biology:

Adult moths are reported to be active mainly at night (Talhouk

1969, Caresche et al. 1969), but a proportion of the population may also be active during the day (Cayrol 1972). After emergence, the adults are induced to fly and feed by cool and humid conditions(Has-

san, Moussa and Nasr-El Sayed 1960). Nasr-El Sayed (1963a,b) report-

ed that the highest percentage of emergence occurs at 30°C. and60% re-

lative humidity. He also indicated that the survival period of both male and female adults is enhanced by high relative humidity. Nasr

and Nassif (1974) found similar characteristics and reported that at

90% R.H. and at a variable temperature, adults of S. littoralis live

longer at lower temperatures (12.2 days at 15°C.) and are shorter

lived at high temperatures (4.05 days at 30°C.). The adult longevity 151 is also shortened when they are reared fromcrowded larvae (Zaher and

Moussa 1961, Rivnay and Meisner 1966), and when hostplants are not suitable (Prasad and Bhattacharya 1975).

The adults begin mating the same night they emergeand females may deposit eggs the same night or up to twonights later (Hassan,

Moussa and Nasr 1960). The eggs are laid in masses of 30-100 on various parts of the host. Individual females may deposit an average of 1000 eggs (Caresche et al. 1969). Nasr-El Sayed (1963b) reported that the number of eggs laid by individual females variedwith humidity. He found that 208 eggs were laid at 0% humidity, but 470 eggs were laid at 100% R.H. Nasr and Nassif (1974) reported that individual females may lay up to 1277 eggs at 69% humidity and at25°C.

The incubation period for eggs was reported to lastthree to four

days at 26°C four to six days at 22°C., and 20-26 days at12°C.

(Rivnay 1962). Upon hatching, the young larvae remain in groupsfor

a short period at the oviposition site(Hassan, Moussa and Nasr 1960,

Gawaad and El-Gayar 1974). Willcocks (1925) stated that for a few

days, the larvae may feed on the lower epidermis of leaves(maize) in

stripes and spots, leaving the hard epidermal leaf veins. He noted

that older larvae eat long slits in maize which gives the plant a

ragged appearance. He added that larvae can also tunnel into the plant

from below ground level. Rivnay (1962) indicated that larvae start

to leave the host plant during the day afterreaching the fourth in-

star (subsequent stages feed mainly during thenight). Rivnay (1962)

also reported that the developmental period of larvae lasts22.7 days 152 at 22°C., 15 days at 26°C. and 14 days at 30°C. Caresche et al.

(1969) reported that the developmental period of larvae in cotton plants required 15-90 days. Cayrol (1972) stated that six larval instars develop but two more may be produced, depending on the temperature.

The mature larvae pupate below the soil level about 3-4 cm

(Appert 1976) or 2-5 cm (Talhouk 1969). Nasr-El Sayed, Moussa and

Hassan (1960) found that 20% soil moisture is most favorable for pupation and adult emergence. Nasr -E1 Sayed (1963a) reported that the pupal period lasts longer at low relative humidity, e.g. 16.6 days at 0% R.H., 3.9 days at 60% R.H., and six days at 100% R.H.

The pupal period at different temperatures was found to be seven to eight days at 23-30°C., and 14 days at 18-20°C. (Rivnay 1962). Nasr and Nassif (1974) reported the following developmental thresholds for the pupae: 90% and 69% R.H. and 12.5 and 12.25°C. respectively for male pupae, and 12.25 and 12°C. for female pupae. For larvae, the developmental threshold was 9°C. at 90% R.H. and 8.25°C. at 69% R.H.

The threshold for development of the eggs was 12°C. for males and females at 90 and 69% respectively.

Several factors have been reported to influence the developmental period of the stages of S. littoralis and to affect the behavior of larvae as well as the physiological processes of adults. Hodjat (1970) and Zaher and Moussa (1961) found that crowding the larvae in the laboratory, increased their activity and shortened their developmental period. It changed the morphometrics of the adults (Zaher and Moussa

1961) and sustained or increased the adult fecundity. It shortened 153 the adult longevity and it sustained or increased the pupal period.

Rivnay and Meisner (1966) reported that high temperatures during larval development reduced adult fecundity. The longest period of adult survival was obtained when the pupal stage developed in 76% R.H.

The developmental period of larvae, fecundity and adult longevity were also affected by the species of host plant(Moussa, Zaher and

Kotby 1960, Salama, Dimetry and Salem 1971, Prasad and Bhattacharya

1975, Harakly and Bishara 1974).

According to Hill (1975) the complete life cycle of S. littoralis

in the moist tropics requires 24-35 days. The moth breeds continuous-

ly during the year and up to eight generations may develop. In Egypt,

seven generations of the moth develop each year(Maher and Rasmy 1969).

Nasr and Nassif (1974) reported that one generation can develop in

25.7 days at 35°C. at 90% relative humidity (laboratory conditions with leaves of sweet potato and castor). Risbec (1950) reported that

during the rainy season in Senegal, the moth developed two generations,

although a third generation has been reported to develop on vegetable

crops. He noted that the complete life cycle of the moth required

about two months (9-11 days on the pupal stage). He also reported that

the larvae diapause during the dry season. In the Sudan, Schmutterer

(1969) indicated that several generations of the moth occur during the

rainy season, but it survives the dry season as a pupa in therainfed

areas.

Control strategies:

Temperature and humidity, more than host availability, appears 154 to influence whether or not S. littoralis reaches the level of minor or major pest. In the drier areas of its distribution, this species is a minor pest as a reuslt of sub-optimal relative humidity (Talhouk

1969) or high prevailing temperatures (Schmutterer 1969).

The moth is reported to be a major pest where irrigated crops have been introduced (Rivany 1962) and in Egypt, legislation has been developed to control irrigation to prevent further distribution of the pest (Cayrol 1972). In addition, migration of the moth (Cayrol

1972) and changes in climatic factors could result in an outbreak of the moth (Rivany 1962).

Agronomical and mechanical control:

In Egypt, where S. littoralis is the most important insect, various methods of control have been suggested and they involve several different techniques. Maher and Rasmy (1969) reported that hand collection of egg masses is the principal method of control and up to 80% of the eggs are destroyed in this way. Weed control, crop rotation, irrigation scheduling and adding petrolium to irrigation water are also used for control of this pest in Egypt. In rice plants,

Grist and Lever (1969) suggested flooding the rice field for two or three days to force larvae up to the tip of the plant where they can be collected and destroyed.

Hosny and Kotby (1960) found that some plants are preferred by the ovipositing female. The list in order of decreasing preference included the following plants: castor (Ricinus communis) cowpea, 155

cotton, maize and sunflower(Helianthus annus). On the basis of host preference, they suggested the use of castor as a trap crop.

Varietal resistance:

Several studies have been reported on the variation inthe grow-

th potential of Spodoptera littoralis on someof its host plants,

although no host resistance has been found.

Moussa, Zaher and Kotby (1960) found 73 plants tobe hosts of S.

littoralis in Egypt. The moths were more injurious to cotton, berseem

(Trifolium alexandrinum) and maize. They reported that larval develop-

ment occurred most rapidly on berseemand slowest on cotton, while

larvae failed to develop on maize. Salama, Dimetry and Salem (1971)

tested 27 plants belonging to 16 botanicalfamilies, and found that

eight were not accepted by the moth, five were eaten to someextent

and 14 supported larval growth. They suggested that S. littoralis

tends to prefer tender plants but avoids tougherplants. Prasad and

Bhattacharya (1975) evaluated 63 plant species in22 families, and

found S. littoralis failed to complete development on sevenplants.

They suggested that failure to develop wascaused either by physical

characteristics of the plant or absence of feedingstimulants and/or

presence of feeding deterrants inthese plants. They reported that

some plants did exhibit antibiosis. They reported that the growth

index (percentage pupation/duration of larvalperiod) of S. littoralis

on 48 of the plant species concluded that the preferred plants be-

long to the class Magnoliatae. The growth index is reported to be an 156 appropriate method for determining suitability of hostsin polyphagous insects. Methods of its calculation are given by Howe(1971),

Srivastava (1959) and Prasad and Bhattacharya(1975).

Biological control:

Various parasites are recorded from S. littoralis. Pearson

(1958) listed the important parasites of S. littoralisin Continental

Africa. In Egypt, great numbers of parasites andpredators of S. littoralis are recorded, but their impact on this species wasreported to be negligible by Talhouk (1969). Brown and Swaine (1965) reported several viruses which are found on S. littoralis.

Risbec (1950, 1960) indicated that parasitism on S.littoralis was high in Senegal and that it caneffectively control populations of the moth. He (1960) listed the following parasites: Tachinidae:

Carcelia evolans Wied, Phorcida inconspicua Meig, Actiaaegyptiaca

Willen; Icheumonidae: Charops sp., Metopius sp.; Braconidae:

Apanteles risbeci de Saeger, A. nioro Risbec, A. sagaxWlk., A. ruficrus Hal.; Chalcidae: Hockeria unicolor Wlk.

Chemical control:

Broadcasting BHC (10% dust at 2.5 kg a.i./ha) or Aldrin bait are

recommended in rice (Grist and Lever 1969). Appert (1967) recommended

the use of Sevin at a rate of one kg a.i./ha on maize and on vege-

tables at a rate of 100 gm a.i./hectolitre water (Appert1976).

Abdel Salem et al. (1972) reported that Fenitrothion,DDT-Fenitro-

thion and Tetrachlorvinphos were effective for controlof S. littoralis

in sweet potato. Gawaad and El Gayar (1971, 1974) indicated that 157

Phorate and gamma BHC were effective soil insecticides against mature larvae, prepupae and pupae of S. littoralis, particularly in soil with 20% moisture content. El-Ibrashy and Abou-Zeid (1972) found that the herbicide EPTC had a strong sterilant effect on female S. littoralis and inhibited oviposition in the laboratory when 250 mg a.i./larva was administered to the last instars.

Maher and Rasmy (1969) reported in Egypt, that S. littoralis has developed resistance to Toxaphene, Tr:ichlorfon (= Dipterex) and

Endrin. They suggested to control S. littoralis that several methods should be used and different insecticides should be applied in limited quantities in different areas. 158

Orthoptera

Locusta migratoria migratorioides (Reiche and Fairmaire)

Oedipoda migratorioides Reiche and Fairmaire 1850

Locusta migratorioides Kirby 1902

Locusta migratoria migratorioides (Rch. & Fr.) Uvarov 1928

Gastrimargus affinis Sjostedt 1931

Gastrimargus morio Sjostedt 1931 (Johnston 1956)

Common name: African migratory locust

Order: Orthoptera

Family: Acrididae

Subfamily: Acridinae

The genus Locusta Linnaeus 1758 has but one species: Locusta migratoria (L.) (Dirsh 1965a, Uvarov 1966), It did include at one time, the species Locusta pardalina (Walker) which was transferred to the genus Locustana Uvarov when Uvarov (1921) revised the genus Locusta which was previously named Pachytilus Fieber. At the same time, Uvarov

(1921) resolved the taxonomy of the two distinct species (L. migratoria

(L.) and L. danica (L.); he showed that there was only one species which, depending on circumstances, was found in different forms. This led to the formulation of the phase theory in order to explain the in-

terrelationships of the different forms and also was thought to explain

the periodicity of locust swarms (Uvarov 1921, 1928). The name phase

solitaria was given to the extreme form "in which the species is repre- sented in a given locality when only isolated individuals are present 159

and no swarms exist or have existed at least one preceding generation".

The second extreme form,phase gregaria, "to which belongs the bulk of

individuals of the species in a given locality when it is forming dense

and large emigrating swarms"; between these two forms were the phase

transiens (Uvarov and Zolotarevsky, 1929, p.262).

The species has a wide distribution, with the form Locusta mig-

ratoriodes (R.& F.) being the swarming phase which occurs in the tro-

pics and subtropics. It was later recognized that there were striking

differences in individual size, degree of development of the gregaria

character, and in the geographical distribution of the swarming forms which occur in different parts of the world. On the basis of these

differences, subspecies of L. migratoria (L.) were raised. Uvarov and

Zolotarevesky (1929) recognized the subspecies L. migratoria rossica

(Uv. & Zol.) from central Russia and western Europe, L. migratoria migratoria (L.) from south eastern Russia, and L. migratoria migra-

torioides (R. & F.) from the tropics and subtropics. Zolotarevsky

(1929) made a division in the latter subspecies and recognized L. mig-

ratoria capito (Saussure) as a distinct subspecies occurring in

Madagascar. Uvarov (1936) made a further split in L. migratoria migratorioides in that he recognized L. migratoria manilensis (Meyen) as being a distinct subspecies, which occurs in south eastern tropical

Asia, Malay archipelago, and the Philippines. Uvarov (1936) proposed

L. migratoria migratorioides as the African migratory locust.

Uvarov (1966) listed eight subspecies of L. migratoria (L.):

L.m. migratoria (L.) (Basin of the Black caspian and Oral areas, central 160

Asia, as far as Northern China), L.m. rossica (Uv. & Zol.) (Central

and Western Europe, European Russia), L.m. gallica (Remaudiere)(South

Western France), L.m. cinerascens (L.) (Mediterranean areas), L.m. manilensis (Meyen) (East, North China, Japan, Philippines, Celebes,

Borneo, Java), L.m. burmana Ramme (Upper Burma, Tibesti), L.m. capito

(Saussure) (Madagascar), and L.m. migratorioides (R. & F.) (Tropical

Africa). Wintrebert (1970) added L.m. remaudieri (Hartz), and stated

that he found no difference in morphology, size or amplitude of phase

variation to justify the distinction between the two subspecies L.m.

capito and L.m. migratorioides and suggested synonymizing the latter

two subspecies.

It has been found that different forms occur in each subspecies

(Solitaria, transiens, and gregaria). Following diverse speculations,

polemics and controversies about the terminology of the phases and the

phase theory, Uvarov (1966) proposed the names Phase solitaria, tran-

siens and gregaria be dropped and to substitute the wording such as

solitarious, gregarious and transient phase to the individual locusts

entering the given stage. In addition, he suggested adopting the

terminology of Pasquier (1952) when estimating the degree of phase

transformation (e.g. solitaricolor (color), solitariform (morphology),

solitarigest (behavior).

Identification:

The taxonomy of the family Acrididae among other Acridomorpha is

treated in Dirsh (1965a). He provided keys and diagnoses for the sub-

families, genera and a list of the African species of each genus and 161

their distribution. Other similar treatments are also found in Dirsh

(1961) and Uvarov (1966). The subfamily Acridinae to which the genus

Locusta is placed includes some notorious pests of cultivatedGraminae

(e.g. Oedaleus senegalensis (Krauss), Aiolopus thalassinus (Fabricius)

(Batten 1968, Joyce 1952, U.S.A.I.D. 1974). The genus Aiolupus Fieber has been revised by Hollis (1968).

Dirsh (1965a, p.483) described the genus Locusta as follows:

Large. Integument smooth; or finely dotted. Antenna filiform about as long as head and pronotum together. Head globular; fastigium of vertex narrowing forwards with obtuse, almost truncate apex, slightly concave, with weak lateral and median carinae; front vertical, excurved fron- tal ridge moderately wide, slightly depressed at ocellus, with parallel, almost obliterated lateral carinulae. Pro- notum tectiform or constricted in prozona and almost saddle shaped; median carina well developed, crossed by posterior sulcus only; metazona slightly longer than prozona, its posterior margin obtuse-angular or almost rounded. Meso- sternal interspace about as long as wide or slightly longer. Elytra and wings fully developed; intercalary veins of medial area strong and finely serrated; anterior part of medial area with dense thickened, transverse veinlets. Hind femur slender. Spurs of hind tibia not specialized. Arolium small. Male supra-anal plate angular. Cercus narrow-conical, with obtuse apex. Subgenital plate conical with subacute apex. Epiphallus with comparatively large ancorae and with large bilobate lophi with strongly separated lobes. Ovipositor short, robust, with curved valves; lower valve with angular, external, lateral pro- jections."

Only one species is recognized in the genus, Locusta migratoria (L.).

The extreme forms of the subspecies L.m. migratorioides are described by Johnson and Maxwell-Darling (1931). Differences are also reported by Faure (1932) and Lean (1936). Uvarov (1928) described the forms of L. migratoria (L.) and some characteristics of the subspecies

L.m. migratorioides. Dirsh (1950) gave a descriptive table and 162 illustrations for distinguishing the instars and their sex. The characteristics of the eggs are reported by Roonwal (1936), Chapman and

Roberston (1958). The latter two authors illustrated the egg pods of different acridid species and provided keys for identifying the egg pods.

Lean (1936, p.166) gave what he termed a "hypothetical" diagnosis of the forms of L. m. migratorioides. He described the extreme forms as follows:

Phase solitaria: (1) color variable, but specially green and mainly black, (2) black streaks on upper surface of pronotum absent,(3) low E/F ratio averaging in male 1.85, in female 1.90,(4) strong sexual dimorphism, (5) male hind tibia pink,(6) two black marks on inside of hind tibia.

Phase gregaria: (1) color brown, males yellow when sexually mature, (2) two black streaks on upper surface of pronotum, (3) high E/F ratio, male averaging 2.17, female 2.20,(4) slight sexual dimorphism, (5) male hind tibia variable in color but not pink, (6) one large black mark on inside of hind femur.

The most striking difference between the two extreme forms is reported

to involve the difference in the shape of the pronotum (Uvarov1928,

Faure 1932, Locust handbook 1966). Morphometrics of the locust and

ratios used to separate the extreme forms are given by Uvarov (1966),

Dirsh (1951), and Wintrebert (1970).

The Locust handbook (1966) indicated that there are usually five

instars in both extreme forms, but six to seven instars can develop in

solitarious individuals during very dry conditions. The length and

weight of the five instars increase from 7-8 mm and 14 mg in the first

instar to 34-37 mm and 1000-1220 mg in the last instar. The general

coloration in solitarious nymphs is of the background, but in 163 gregarious individuals, it is brown or black. Faure (1932) stated that in gregarious individuals the color was due to muscular activity, while isolated individuals developed nutritional or imitative color.

Albrecht (1965) reported that color polymorphism in isolated individuals is tied to humidity.

According to Roonwal (1936), the freshly laid eggs are pale yellow in color. They become greyish at the time of blastokinesis, and when they are about to hatch, become dirty brown. Their shape is that of a slightly curved cylinder. The eggs increase in size from about

5.68 x 1.18 mm to 7.85 x 1.99 mm due to water absorption from the sur-

roundings. The eggs are laid in the ground in a pod which is variable

in shape and length (Uvarov 1928, Chapman and Roberston 1958).

Distribution:

The geographical distribution of the African migratory locust

falls in Tropical Africa since the subspecies was separated from the

one in Madagascar (Zolotarevsky 1929) and the one inthe Far East

(Uvarov 1936). The distribution of the locust is generally reported

in terms of areas liable to be invaded by the locust during periods

of plague and areas considered as outbreak centers of the locust.

The outbreak areas which are an essential component of the phase

theory of locusts are defined as areas in which the locusts find the

best conditions for survival and where the process of gregarisation

can take place, which may subsequently lead to escapeof swarms once

they are formed. Albrecht (1970, p.108) defined outbreak areas as

"areas where life can be permanently sustained without the intense 164

migratory activity, mainly because the different environments required

at different times of the year are less widely separated", whereas

the invasion areas "are places where locusts are able to survive and to multiply during periods of maximal abundance, but where life cannot be

permanently sustained owing to the violence of population change once

population has been overtaken by catastrophe".

Analysis of the origin of swarms of the African migratory locust

during the plague period 1881 - 1902 led Lean (1931a) to suggest the

flood plains of the middle Niger (Mali) as being the major outbreak

center for the locust. This was later confirmed by Lean (1936) and

Zolotarevsky (1938). Since that time, various investigations have de-

fined in great detail the habitat and the dynamics of the locust in

that area. They have extended the area to include the surrounding

arid and semi-arid land (Davey 1956, 1958, 1959). Other areas in Con-

tinental Africa were also recognized but were given a marginal status

(Uvarov 1957), although recent accounts classify them as important.

Wintrebert (1973) indicated that there are four outbreak centers for

the African migratory locust: flood plains of the Niger (Mali), North-

east states in Nigeria, Kassala and Blue Nile province in the Sudan,

and Southwest Madagascar. The first three areas are in Continental

Africa in the zone of short rainy season, and are situated roughly be-

tween 12 and 17°N latitude.

The Locust handbook (1966) reported that the solitarious individuals of the African migratory locust have a wide distribution in Africa and the Middle East. It listed the following countries which were 165 invaded by the locust during the plague period of 1928-1941: Angola,

Botswana, Burundi, Cameroun, Central African Republic, Chad, Congolese

Republic, Dahomey, Ethiopia, Gambia, Ghana, Guinea Republic, Ivory

Coast, Kenya, Lesotho, Liberia, Malawi, Mali, Mauritania, Mozambique,

Niger, Nigeria, Rhodesia, Ruwanda, Senegal, Sierra Leone, Somalia

Republic, South Africa, Southwest Africa, Sudan, Tanzania, Togo, Uganda,

Voltaic Republic, and Zambia.

After examining data of the two plague periods, Betts (1961) concluded that the most frequently infested territories were in western

Africa and extended eastwards to include Sudan and Zaire. Batten

(1966) reported that the last plague (1928-1941) covered about 6,650,000 square miles. In the event of another escape of swarms from the outbreak area in Mali, he estimated the minimum time that would elapse before countries in western Africa would be invaded was six to eight months, in eastern and central Africa ten to 18 months, and in South

Africa 26 to 35 months.

Hosts:

LePelley (1959) listed many plant species fed upon by the African migratory locust in East Africa. Among cultivated Graminae he listed:

Oryza sativa, millets, Sorghum spp, Zea mays, saccharum officinarum, eleusine coracana, and pastures. The nongramineous plants included:

Arachis hypogea, Glycine max, Phaseolus sp, Pisum sativum, Mangifera indica, manihot esculentus and Musa sapium. He concluded that grain crops and monocotyledonous plants are generally preferred. Lean (1931b) stated that the adults of the African migratory locust feed almost 166

entirely on plants of the order graminae and mainly maize, guinea corn,

millets, rice and sugar cane of the cultivated crops. During the dry

season, they occasionally attack coconut, oil palm, plantain, pineapple,

sisal and others. The feeding on the last group of plants is a search

for water rather than food. Johnston and Maxwell-Darling (1931) also

indicate that wild grasses and gramineous crops are the main host for

the locust. They found that the nymphs reach maturity more readily

on plants such as Sorghum vulgare and Pennisetunm typhoideum than on

cotton. The Locust handbook (1966) indicated that during the recession

period, the locust feed mainly on wild grasses and cereal crops and

noncereal crops are damaged only in the absence of cereal crops or at

times when grasses dry out. Kozhanchikov in Uvarov (1966) listed

several botanical families which are highly variable with respect to

their effect on the development of a similar subspecies, L. migratoria

migratoria (L.). He found that the locust can complete its life cycle

in some families (e.g. Graminae, Cyperaceae), but on others only the

nymphs develop, often with high mortality, and adults do not mature

sexually (compositae cruciferae, some Graminae (.avena), Leguminosae,

Plantaginaceae, Urticaceae); on other hosts, nymphs can reach the last

instar but mortality at the final moult and subsequent stages is high

(Rosaceae, Caryophiliaceae, Saxifragaceae); only the first instar de-

velops (Typhaceae, Ranunculaceae); the early instar eats the plants but

fails to moult (Labiatae, Onagraceae, Chenopodiaceae, Liliaceae, Ger- aniceae, Betulaceae, Ericaceae), and a last group of plants which are

not eaten by the first instar, even upon starvation (Primulaceae, 167

Polygonaceae, Convolvulaceae, Rubiaceae, Salicaceae, Caprifoliaceae,

Ulmaceae).

Damage:

Damage from the African migratory locust results from the locust

feeding on the foliage or on any other aerial part of the host plants.

There are also reports which state that the locust prefers to feed on

the milky ripe stage of gramineous crops (Maxwell-Darling 1948,

Schmutterer 1969, Joyce 1952). Bullen (1966) indicated that the

severity of damage by locust in general is related to the growth stage

of the host. He quoted that, in Kenya, the African migratory locust

reduced the yield of maize to zero when the crop was three to five

feet high at the time of flowering. The yield was reduced by 20% if

the attack occurred after the grain had formed but has not rippened.

The yield was unaffected or even improved if the attack occurred when

the crop was 12 to 18" high.

The two plague periods when the locusts did severe damage have

been reported. The first extended from 1890 to 1904 and the second

from 1928 to 1941 (Betts 1961, Batten 1966). During the first plague

period, damage by the locust induced famine in Chad, Cameroun and the

Congo. During the second period, estimated crop losses ranged from

50% to 40% on wheat and maize crops respectively in Kenya (1931)

(Bullen 1966), to 40% of the rice crops in Guinea (1940) (Locust hand-

book 1966), or to several million dollars in the invaded areas

(C. Agr. Pr. pays chauds. 1968b).

Batten (1966) estimated the infestation frequency of adult swarms 168 and nymphs in several countries during the last general invasion by the locust. The infestation frequency of the swarms (percentage of time in which swarms have been reported in the given country during a

157 month period) were 76 for Mali, 54 for Senegal, and 22 for Mauri- tania. The frequency of infestation by nymphs during the same period was 43 in Mali, 22 in Senegal and 17 in Mauritania. He also reported on "the estimated potential minimum number of months between the escape of swarms and invasion", and found it to be zero in Mali, six in Senegal and five in Mauritania. The source of invading swarms was the flood plains of the Niger (Mali), located between 13 and 17°N latitude and 3 and 6°W longitude.

Like many other locusts, the economic status of the African migratory locust stems from it being able to inflict heavy damage over large areas during the period when the locusts occur in swarms. How- ever, unlike the desert locust, there are well recognized outbreak areas of the African migratory locust. Continuous surveillance in these areas has prevented plague formations since the last one ended

in 1941 (Batten 1966, Wintrebert 1973, Betts 1975).

Several studies have described the main features of the outbreak areas of the African migratory locust and the dynamics of the locust populations in these areas. These studies have been conducted primarily in the flood plains of the Niger (Mali) and its associated semi- arid and arid lands (Lean 1936, Zolotarevsky 1938, Remaudiere 1954,

Davey 1958, 1959, Descamps 1961, 1962, Farrow 1970, 1975). Uvarov

(1957) also summarized the essential elements of the area and the 169 ecological requirements favorable to the locust.

These studies revealed that the area is a complex of well-defined habitats for the locust. The diverse habitats grade into one another and are seasonally suitable for the locust's annual cycle. The hab-

itats complement each other and provide the basic requirements for

formation of swarms. The area is generally divided into the flood

plains per se and the surrounding sahelian lands. The locust will

breed in the sahelian lands during the rainy season (July-September)

at the time when the plains are flooded. At the onset of the dry sea-

son, the locust population move back to the plain and begin breeding

as the flood water recedes (October-April). The inlands within the

flood plains allow the locust to breed during the early part of the

rainy season (May-June). The overall picture of the area is a series

of habitats which are colonized at different times of the year, allow-

ing the locust to develop four to five generations annually (Betts

1975).

Farrow (1970, 1975) stated that the events leading to plague for-

mation can occur during one annual cycle of the locust, particularly

with a sequence of above-average, late and early rains. Betts (1975)

concluded that the main factors contributing to the onset of plague

formation is the mass multiplication of the locusts and an increase

in density of the population during the rainy season, combined with the

dynamics of the floods which, when slow, allow individual locusts to

concentrate on small areas which are uncovered. These factors start

the gregarisation process which occurs in early instars and could be 170 achieved with 30,000 adults/ha or at egg pod densityof 1/m2 (Farrow

1970).

Batten (1967) suggested that the movement of swarmsduring the last plague (1928-1941) was downwind, and theseasonal change in distribution was a response to the latidunaldisplacement of the intertropical front and its associated wind fields. In Nigeria, Lean

(1931b) concluded that the area of dispersal of swarms(1929-1931) was limited by humidity. Swarms remained where the relative humidity was not more than 85% and not less than 40%. Most swarms were found in the humidity gradient 80-60% which coincided with three main vegetation belts: high grass-low tree savanna, accacia-tall grass savanna and accacia-desert savanna. The swarm moved across the belts in response to humidity changes.

Biology:

Many aspects of the African migratory locust biology are presented by Uvarov (1928, 1966). He also reported on differences in the bionomics between the extreme forms of the locust. The investigations

conducted in the flood plains of the Niger provided treatments onthe

subject with particular reference to the specific habitatswhere the

locust was studied. Farrow (1975) reported the most recent treatment

of the biology. The Locust handbook (1966) identified the essential

elements of the life history of the locust, which according tothe

report, is similar to that of the desert locust exceptfor the number

of instars.

There are three stages in the life history of thelocust: 171 eggs, nymphs (hoppers) and adults, and their developmental periods are affected by environmental conditions. Hamilton (1936, 1950) found under laboratory conditions, that the duration of the adult life of the locust is closely tied to sexual maturation which is affected by humidity and temperature. The more rapid the sexual maturation, the shorter the length of the adult life. He found that the optimum constant relative humidity and temperature for sexual maturation was

70% R.H. and 39.4°C. Lean (1931b) found that the length of adult life

through the dry season in Nigeria was 22 weeks. Descamps (1961) reported that the adult life lasted up to three months during the wet season in the Niafunke zone of the main outbreak area. According to

Uvarov (1966), crowded females lived an average of 45 days (82 days maximum), while isolated individuals lived an average of 30 days (65 days maximum). The Locust handbook (1966) indicated that the soli-

tarious population started laying eggs ten days after fledging, while

it took 2 1/2 to 3 months in gregarious individuals for the same process.

Lean (1931b) used degree wetness (monthly degree wetness = M.D.W.=

RxD/100; R = total rainfall during the month, D = number of days with more than 0.1 inch of rainfall) to define the breeding period of the

locust. He found that breeding would not occur after the dry season until the M.D.W. reached two and the relative humidity rose to 60% and no breeding occurred above 80% relative humidity.

Popov (1959) found that soil temperature of 30-34°C. were the most favorable for oviposition. The eggs are laid mostly in moist 172 compacted silt soil. The mean number of eggs/pod varies from 50 to 72 and depending on the season, the incubation period of the eggsis

21-33 days. Descamps (1961) also found that temperature, humidityand nature of the soil affected the incubation period. The period lasted

40 days during January-February and 20 days during March. In heavy soils, the incubation period lasted up to three months. He also noted that there was a variation in the egg incubation period between generations of the locust. Davey (1959) reported that moisture content and soil temperature were the most important microclimate factors in relation to oviposition, incubation period and hatching. He found

in caged populations that an incubation period of 15-20 days was

common, 25 days was not exceptional and 9 days was recorded but once.

Batten (1967) reported from field data that the incubation period was

13 days in Mauritania, 9-15 days in Senegal and 12-20 days in Mali.

The most common incubation period was 10-15 days in the invaded area during the last plague of the locust, with the exception to Cameroun

(17-20 days). More than two egg pods per individual female are not

uncommon and depending on the season, egg pods may belaid at differ-

ent intervals (Locust handbook 1966). The eggs can be submerged in

water for some time without being destroyed, particularly whenthey have

reached the blastokinesis stage or are in embryonic diapause (Popov

1959).

Five nymphal instars occur in both solitarious and gregarious

individuals, and development is completed in 30-60 days (Locust hand-

book 1966). Davey (1959) reported that the average duration of the

five nymphal instars was 32 days for the Sahelian generation (those 173 bred in the semi-arid land), or a range of24-36 days for the plains generations (those bred in the flood plains duringthe dry season).

Descamps (1961) reported that most males gothrough five instars, but females pass through six or seven instars. Faure (1932) found that five instars develop during a period of eight to tenweeks. Johnston and Maxwell-Darling (1931) reported a developmentalperiod of 27-30 days for nymphs arising from solitarious individuals. Batten (1967) reported the developmental period of hoppers arisingfrom swarming populations as follows: 40-50 days in most of the invasion areas,

30 days in Sierra Leone, and 67 days in Cameroun.

Hamilton (1936, 1950) reported that 65 to 80% relativehumidity was the optimum constant relativehumidity for hopper development and

resulted in the highest percentage of hoppers reaching theadult stage.

The minimum temperature threshold for development is11.7:C. and the

upper temperature limit for developmentof eggs and hoppers is 47.8°C.

The highest percentage of hoppers reaching theadult stage was at 34.4°C.

The complete duration of the life cycle of theAfrican migratory

locust is variable. Hamilton (1936) reported that the length of the

life cycle in the laboratory depends on humidity, temperatureand the

generation of the locust. In the main outbreak areas of Mali, the life

cycle coincides with the season and four to fivegenerations of the

locust develop/year. Some locusts develop in the flood plains as the

water recedes, others on the inlands of theplains, and still others

in the semi-arid and arid lands. In the arid lands, fields which are

abandoned and fallowed are preferred oviposition sitesfor the locust. 174

The seasonal migration of the locust which is influenced by the wea-

ther, causes populations to move from habitat to habitat and main-

tains the annual life cycle (Uvarov 1957, Davey 1959, Farrow 1970,

1975, Betts 1975).

Control strategies:

Control strategies of the desert locust and the African migra-

tory locust involve similar methods (Gunn 1960, 1975, Uvarov 1928,

Maxwell-Darling 1948, Locust handbook 1966). They are discussed under

the desert locust (Schistocerca americana gregaria (Forskal).

Unlike the desert locust, the African migratory locust has well-

developed outbreak areas. These areas are recognized as being

potentials for swarm formation which can leave the areas and migrate

over a large number of African states south of the Sahara. This led

Uvarov (1928) and Gunn (1960, 1975) to report that the strategy of

control should involve primarily preventing plague formations by

monitoring the locust in these areas, what Gunn (1960) has termed

"outbreak area control".

The discovery of the major outbreak area of the locust led to the

formation of an international organization: Organisation Internationale

Contre le Criquet Migrateur Africain (0.I.C.M.A.) (Anonymous 1957).

The organization is devoted to the control of the locust and monitors

the locust population in the outbreak areas. It has several units of

control throughout these areas and the principal method of control is

with insecticides (Gunn 1960, 1975). 175

Natural mortality in the field population of the locust is reported to be high. Popov (1959) found in the flood plains of the Niger

(Mali) that predation cuased about 40% mortality and parasitism about

13.5%, both during the egg stage. The main parasite is Scelio sudanensis Ferriere (95% of the parasitism) and Scelio remaudierei

Ferriere. Davey (1959) stated that parasitism never exceeds 1% in the hopper and adult stage. Uvarov (1928), Greathead (1963) and Dempster

(1963) gave additional accounts on important parasites and predators of the locust as well as of other acrididae. Wintrebert (1973) noted that the location of the outbreak areas of the locust in Continental

Africa falls within the distribution range of important bird predators

(Merops nubicus, Chelictinia riocourrii, Bustatur rufifennis,

Eurystomosus flaucurus afer, Aerops albicollis). 176

Schistocerca americana gregaria (Forskal)

Gryllus gregarius Forskal 1775

Acridium perigrinum Oliver 1804

Acridium tartaricum Latreille 1804

Gryllus rufescens Thunberg 1815

Acridium sellatum Walker 1870 (Dirsh 1974)

An extensive list of synonyms is given by Johnston (1956).

Common name: Desert locust

Order: Orthoptera

Family: Acrididae

Subfamily: Cyrtacanthacridinae

For many years, the desert locust has been known under the name

Schistocerca gregaria (Forskal). Recently, it was given a subspecies

0 rank by Dirsh (1974). Dirsh redescribed the genus Schistocerca Stal

along with its species and subspecies. He stated (p.19) that,

The genus Schistocerca is morphologically clearly defined, but its species [22] form numerous infraspecific taxa, subspecies, forms, local races, variations, ecological forms, which are difficult to define and more difficult to separate clearly.

He indicated that the genus originated in the new world on the basis

that it has no close affinity to any other genera in the subfamily

Cyrtacanthacridinae in the old world. He invoked the dispersal power

of the genus to explain the wide colonization in other areas. Dirsh

(1974) placed the origin of the subfamily Cyrtacanthacridinae in the

Eocene and Oligocene when arboreal vegetation was dominant. He 177 indicated that the subfamily started to decline at the onset of herbaceous vegetation during the Miocene and Pliocene and concluded the

explosive speciation of the genus Schistocerca is of recent origin and is still in process. Mishchenko (1965) suggested the Miocene as

the period of greater exchange of fauna (especially in the genus

Schistocerca) between the new world, Western Eurasia and North Africa.

Shcherbinovskii in Dirsh (1974), puts the origin of the genus

Schistocerca in the Mesozoic and suggested that its differentation

took place later in Tertiary. The phylogeny and the evolutionary

trend of the Acrididae was also discussed by Sharov (1971).

Haskell (1970) stated that the earliest record of locusts were

the carvings on egyptian tombs about 2400 B.C. The Locust handbook

(1966) noted that the desert locust could invade 20% of the world land

mass and could affect 1/10 of the world population. Mishchenko (1965)

reported that the first recorded data of damage done by grasshoppers

and locusts was 1490 B.C. Bullen (1966) estimated the loss in grain

sorghum due to the desert locust in Eritrea in 1958 to be 43,000 tons;

this amount would have fed 200,000 people for a year. In Senegal, it

was estimated that 16,000 tons of millet and 2000 tons of other crops

were lost due to the locust in 1957 (Locust handbook 1966). The aver-

age annual cost to control the locust in the "French WestAfrican"

states is reported to be $1,000,000 (C. Agr. Pr. Pays chauds 1968a).

Haskell (1970) stated that approximately $20,000,000 is spent annually

all over the world to keep locusts in check. The potential threat of

locust and grasshoppers has been stressed by Uvarov (1957, 1961, 1964), 178 and he particularly stressed the danger of the locusts whendeveloping new lands in arid orsemi-arid areas.

The literature on the desert locust and locusts ingeneral is overwhelming. Johnston (1956) stated that the literature pertaining to the subject comprises several thousand papers. In "French West

Africa", Mallamaire (1948), Mallamaire and Roy (1959), Descamps(1967),

Anonymous (1975c) and recently, papers given during the plant protection training in Dakar, February and March, 1975(Senegal), reported the essential elements of the biology, dynamics and surveymethods of the locust (e.g. Betts 1975, Popov 1975). Authorative works of Uvarov

(1928, 1966, 1977), Rao (1960), Albrecht (1967), Mishchenko(1965),

Waloff (1966), Hemming and Taylor (Editors 1972), Dirsh (1965a,b,1974,

1975), Locust handbook (1966), along with reviews of Gunn (1960),

Dempster (1963), Bhatia and Singh (1964) cover most of what is known about the locust and similar species.

Identification:

The taxonomy of the genus Schistocerca is treated in Dirsh (1965a, b, 1974), Uvarov (1966) and Mishchenko (1965). Keys to the species and subspecies of the genus are given in Dirsh (1974) along withthe redescription of the genus and its species and subspecies. The Locust handbook (1966) described the desert locust and previous descriptions are given in Uvarov (1928). Dirsh and Uvarov (1953) gave the taxonomy of the genus Anacridium, which is placedin the same subfamily as Schistocerca. The former genus (Anacridium) comprises the so called

Sahelian tree locust whose economic importance is assessed by 179

Popov and Ratcliffe (1968).

Uvarov (1921, 1928) is credited with showing that different names were applied to what in fact was one species (Locusta migratoria (L).

The mistake was brought about by the capacity of the locust to occur in more than one form. Faure (1932) corroborated the findings in

South Africa. Following the discovery, the extreme forms of locusts were named solitaria and gregaria, and the intermediate ones transiens

(Uvarov 1921, Uvarov and Zolotoraysky 1929). The whole idea under- lined a "Cyclomorphism", which is induced by the biological and ecological factors governing locust species.

Dirsh (1974, p.71) renamed the extreme forms of the desert locust and redescribed them as follows:

Forma compressa: It differs from the next form by the following characteristics: body in male longer, in female shorter than in next form; tegmina in male longer, in female shorter than in next form; head relatively wide. Interocular space or vertex relatively wide. Pronotum slightly saddle shaped. Metazona of pronotum relatively wide and shorter; its posterior margin almost rounded. Mesosternal interspace rectangular, wide; Metasternal interspace wide; the form was previously named phase gregaria. Forma tectata: differs from the previous one by the following characteristics: body in male shorter, in female longer than in previous one. Tegmina in male shorter, in female longer. Head relatively narrow. Interocular space in vertex relatively narrower and longer. Pronotum slightly tectiform. Metazona of pronotum relatively narrower and longer; its posterior margin obtuse angular. Mesosternal interspace narrow; in basal part constricted. Metasternal interspace narrow, constricted in middle. The form was previously named phase solitaria."

The Locust handbook (1966) noted that the immature adult is pink

in color but can change to brownish if more than two months are spent 180

in the immature stage. The sexually mature adult is yellow; the male

being brighter than the female. Generally, the phase gregaria is known

to be pink in color when immature, and bright yellow when mature.

The solitaria is light grey to greyish green in all stages (Uvarov

1928, Rivnay 1962, Mishchenko 1965).

Morphometric measurements are used to distinguish the forms.

Uvarov (1921), Dirsh (1951, 1953), Symons (1969), Roonwal and Bhanatar

(1966), Stower, Davies and Jones (1960), and Bhatia and Harjai (1967)

are among the authors who reported different techniques used to separ-

ate the extreme forms of the desert locust. Uvarov (1966) pointed out

that the use of ratios between two body parts are the most useful

techniques for distinguishing morphs of locusts.

The ratios E/F and F/C (E = length of elytron (tegmen); F =_length

of the hind femur; C = width of the head) are used to separate the ex-

treme forms of the desert locust. Dirsh (1953) suggested treating the

sex of the forms separately since they differ in ratios, and he indi-

cated that the E/F ratio is not reliable. Dirsh (1953, 1974) illus-

trated the various organs which could be measured and provided tables

on morphometrics of the desert locust. The F/C ratio is lower in gre-

garia (3.15 and below) than in solitaria (3.75 and above).

According to Dirsh (1974), the desert locust has five to six

nymphal instars and one prenymph, "often called vermiform larva, which

is the first real instar". He described the usual five instars and

the prenymph. Descriptions of the immature stages are also found in

Uvarov (1928), the Locust handbook (1966) and Mishchenko (1965). 181

Stower (1959) illustrated the color pattern of the nymphs by means of a Munsell book of color.

The instars look like the adults except they are wingless and the head is larger in proportion to the body. The head decreases in size from instar to instar, but the antennal segment increases: 13 in the first instar, 19 in the second, 21 in the third, 23 in the fourth, and 25 in the fifth (Mishchenko 1965). Comparatively, the adult has

27-30 antennal segments in solitaria individuals and 26 in adult gregaria (Bhatia and Singh 1964). Rudiments of wing and tegmen are distinct from the third instar and become sizeable by the fifth instar.

They become functional only after the last moult which produces the so called fledglings (immature adults) (Locust handbook 1966).

Mishchenko (1965) stated that the adult tegmena always overlaps the wings and have well-developed longitudinal and transverse veins, which distinguishes adults from final instars. There is a gradual increase in the size and weight of the instars; from 7 mm and 30-40 mg in the first instar to 50 mm and 1000-1200 mg in the fifth instar

(Locust handbook 1966).

According to Dirsh (1974), the newly laid eggs are light yellow in color and turn brownish during their development. The size of the egg is 7.3-9.0 mm in length and 1.5-2.0 mm in width. Uvarov (1928) reported the egg size as 8 mm in length and 1-1.2 mm in diameter. The eggs are laid in the ground and are enclosed in a frothy secretion which hardens and forms an egg pod. The length of the egg pod is about 30-40 cm and its bottom may lay about 10 cm down in the soil, 182

(Uvarov 1928, Dirsh 1974, Locust handbook 1966).

Distribution:

According to Uvarov (1928), the desert locust distributionis

connected with dry desert and semi-arid regions. More recently, the

geographical distribution of the desert locust was presentedin terms

of breeding, migration and the invasion areasof the locust. Waloff

(1966) reported that the invasion areas of the locuststretches over

111 degrees of longitude, from the Atlantic coast seaboardof West

Africa to Assam. Its widest points extend from 40°N in Turkey to10°S

in Tanzania. The total area is over 29 million square kilometers.

The breeding area is divided into spring, summer and winterbreeding

belts which are interconnected by the seasonal migrationof the locust.

The Locust handbook (1966) noted that the mean annual rainfallin the

invasion area is under 500 mm (50-200 mm). The handbook also listed

countries liable to invasion by the locust: Afghanistan, Algeria,

Bahrein, Burundi, Cameroun, Canary Islands, Cape Verde Islands,Central

African Republic, Chad, Congolese Republic, Cyprus, Dahomey,Ethiopia,

French Somali, Gambia, Ghana, Guinea Republic, Hadramault, Ifni,India,

Iran, Iraq, Ivory Coast, Jordon, Kenya, Kuwait, Lebanon,Lybia, Madeira,

Mali, Mauritania, Morocco, Muscat and Oman, Nepal, Nigeria, Niger,

Pakistan, Portugal, Portuguese Guinea, Qatar, Rwanda, Saudi Arabia,

Senegal, Sierra Leone, Socotra, Somalia Republic, South Arabian Fed-

eration, Spain, Spanish Sahara, Sudan, Syria, Tanzania, Togo,Trucial

Oman, Tunisia, Turkey, Uganda, United Arab Republic, VoltaicRepublic,

U.S.S.R. (Uzbekistan, Armenia, Turkemenisten, Tadhiskan), Yemen. 183

Dirsh (1974) added the African state of Zaire to theabove countries and noted that these records involved bothbreeding and invasion areas of the locust. He quoted various sources which recorded the locust in Madagascar, Ceylon, Greece, British Isles,Australia, Den- mark and in a number of Atlantic Islands.

Schmutterer (1969) indicated that the solitarious locusts ofthe

Sudan occur mainly in semidesert and short grass savannaof the so called Sudan belt, south of the Nubia and Sahara. Rao (1964) noted, in India, that the solitarious form of the locust isconfined to sandy areas covered with scrub vegetation. In Western Africa, the habitat of solitarious individuals is reported to be the open, sandy steppes with vegetation consisting of perenial bushes and low herbaceous plants (Locust handbook 1966). In the Sub-saharian zone of West Africa,

the vegetal association Tribulus/shouwia is considered the mainhar- bor of solitarious locust (Popov 1975).

Hosts:

The Locust handbook (1966) listed several families ofplants not

related botanically, which are fed upon by the desert locust. Among

the cultivated plants are: Bulrush millet (Pennisetum typhoideum),

sorghum, maize, wheat, barley, rice, sugar cane, fruit trees, cotton,

pastures, and to some extent coffee. The wild food plants eaten by

the immatures of the locust in Eastern Africa include: Graminae

(Aristida spp, Cenchrus biflorus, Cenchrus ciliaris, Latipes sene-

galensis (among others), Leguminosae (Accacia spp, Cassiaspp),

Acanthaceae, Nyctaginaceae, Burseraceae, Euphorbiaceae, Tiliaceae, 184

Capparidaceae, Boroginaceae, Cruciferae, Solanaceae, Sterculiaceae,

Malvaceae, Salvadoraceae and Zygophyllaceae.

Mishchenko(1965) reported in the Soviet Union, that the locust is injurous to cotton, alfalfa, wheat, barley, maize, flax, tobacco, and tomato. Bhatia and Singh (1964) reported from India, that the locusts eat almost any vegetation and only Calotropis spp, Azadirachta indica,

Dalbergia sissoo, onion and Syzygium cuminii are completely avoided or only partially fed on by the locust. Mann and Burns in Uvarov (1928)

listed Tamarix, Acacia arabica, Prosopis spicigera and Calotropis

giganta as the plants not eaten by the locust. Bullen (1966) classi-

fied the locust as a mixed feeder but he indicated that some reports

indicate dycotyledonous plants, including trees and shrubs are pre-

ferred hosts of the desert locust.

Damage:

The desert locust feeds on the foliage or on any other aerial

parts of the host plant. Severe injury may result in complete defolia-

tion and destruction of the plant. The immature stages prefer the

grain of sorghum and Pennisetum species when they are in the milky

stage (Schmutterer 1969). Pfadt (1971) indicated that grasshoppers,

in general, can also damage the host by biting the stems of small

grains which sever the heads, feed on ripening kernels causing exten-

sive shattering, and feed on the silk (corn) which subsequently pre-

vents fertilization and filling of the ears.

Several authors classify the desert locust as a sporadic pest,

because the severity of the damage is a function of the physiological 185 status of the locust individuals and to their density. The capacity of the locust to form swarms of millions of individuals outweighs any other element in defining the pest status of the locust.

Davey (1954) found that the total consumption of an individual

locust, between hatching and becoming mature, averaged about 30.7 gm

in males and 44.3 gm in females. He calculated that hoppers in all

instars, ate an average of one gm/gm body weight/day. The adults ate

approximately half a gm/gm body weight/day. The Locust handbook (1966)

suggested that one ton of locusts (half a million individuals) could

consume in one day, as much as "10 elephants, 25 camels or 250 people".

Bullen (1966) noted that a swarm of about ten square miles of the

locust has a grazing potential of 150,000 head of cattle. He reported

that an analysis of 2000 cases of damage by the locust showed that 8%

of the damage was caused by the hoppers, 58% by immature swarms, 11%

by swarms of mixed maturity and 23% by mature swarms. He further

noted that 20 adult grasshoppers/square yard can destroy 50% of the vegetation. Pfadt (1971, p.253) stated that in the United States

"some of the worst dust bowls have followed grasshopper outbreaks".

The damage potential of the desert locust has been assessed by

Bullen (1966, 1969, 1970). He developed what he called a Crop Vulner-

ability Index (C.V.I.) which "represents the relative probability of

the occurrence of locust damage to a particular crop in a defined geo-

graphical area" (Bullen 1966, p.162). It also 186

combines the frequency given in terms of the number of years out of 25, during which swarms occurredin the area, in each month of the vulnerable periodof growth of each major crop, with the acreage and average production, in wheat equivalent terms, of each crop grown in the same area. (Bullen 1970, p.167)

The geographical unit is one degree square (10 of latitudeand longitude). The crop vulnerability index of 49 crops has been developed by Bullen (1969). He concluded from the national indices (sum of all

the C.V.I. of all degrees square of the given area) that 50%of the potential damage is liable to occur in the Indo-Pakistan region, 23%

in North West Africa, 2% in West Africa, 11% in eastern Africa, and

13% in the Middle East and Arabia.

Long and careful records of swarms of the locust provided, in

addition to the C.V.I., data on swarm frequencies of the locust. Lean

(1960) reported the annual and monthly frequencies of hoppers and

adult swarms for the period 1949-1959. Waloff and Conners (1965) re-

ported the percentage out of 324 months in which infestation was re-

corded in several countries. The data for Mali, Mauritania and Senegal

are 31, 43 and 26% respectively for the adult swarms,and 11, 19 and

6% respectively for hopper infestation. The Locust handbook (1966)

reported the annual and monthly frequencies of adult swarms and hopper

infestation by degree square. The annual frequency for adult swarms

(1939-1963) was 19 in Mauritania, 18 in Mali and 15 in Senegal. For

hopper infestation, the frequency over the same period was 16 in

Mauritania, 13 in Mali and 9 in Senegal.

The economic status of the desert locust is a result of individ-

uals being able to form swarms of millions, whose activity may last 187 several years, resulting in a period of plague (Uvaory 1928, Gunn

1960, Waloff 1966). The phase theory was conceived by Uvarov (1921) and reviewed by several authors (e.g. Uvarov 1928, 1966, Gunn1960,

Kennedy 1956, Albrecht 1962). The theory was thought to explain locust periodicity, but failed to do so (Dirsh 1974). Phase transformation was essential during the last desert locust upsurge

(Bennet 1975).

Three processes are considered important in the genesis of a plague: concentration of the locust in a given area; mass multiplication and increase in density; and gregarisation of individuals

(Uvarov 1928, Kennedy 1939, Waloff 1966, Roffey and Popov 1968, Locust handbook 1966). The processes are interrelated and are of equal importance and depend on the physiological status of thelocust and on the environmental conditions surrounding the locusts. On a larger scale, concentration of individual locusts may be caused by the seasonal migration of individuals to their breeding zones. The migration is under the influence of synoptic weather because individuals are attracted to areas of air flow convergence where precipitation immediately occurs (Rainey 1951, 1958a,b, 1963, 1969, Sayer1962, Aspliden and

Rainey 1961). In addition, the locust is able to sustain long flight

(Rao 1964, Roffey 1963, Ellis and Ashall 1957). On a small scale, the concentration of locusts can result from the vegetation acting as a

trap, limited suitable laying sites, patchy vegetation,tendency of

females to lay in groups and reduced flying activity of individuals at breeding time (Waloff 1966). Given favorable conditions (Sufficient 188

moisture, vegetation, bare ground), mass multiplication and increase

in density of individuals leads to gregarisation. This is a sum of

processes by which individuals (adults and hoppers) form a cohesive

group as a result of conditioning to one another. The ultimate end

result of all processes is the migratory habit and the ensuing swarms

formation. Roffey and Popov (1968), Bhatia, Singh and Sikka (1970)

reported the presence of nonswarming grasshoppers in locust popula-

tions can accelerate the gregarisation process. Ellis and Ashall

(1957) reported that band formation in hoppers occurs when egg pod den-

sity is greater than 0.25 per square foot. Popov (1975) noted that

gregarisation of adults can begin when their density reaches 300/ha.

Roffey and Popov (1968) found that change from solitarious behavior to

gregarious behavior can begin in as few as five days.

According to Waloff (1966) and the Locust handbook (1966), it is unlikely that the phenomena which leads to plague formation occurs in one generation within a single habitat. Rather, it is an ongoing pro-

cess which may take several generations within complementary areas.

Roffey, Popov and Hemming (1970) reported that swarms can form in sol-

itarious populations and their outbreak can lead to plague formation.

There have been numerous attempts to define whether or not plague of the locust occurs periodically. Rivnay (1962) suggested that an

11 to 13 year cycle corresponds to the periodic invasion of the desert locust in the Near East. Shcherbinovskii in Dirsh (1974) connected the appearance of locusts with solar activity and advanced the idea that an 11 to 22 year cycle corresponds to the upsurge of the locust. 189

However, Waloff and Green (1975) could not find evidence for locust

periodicity after analyzing several plagues of the locust which

occurred since 1860 or 1900.

Biology:

Several authors have investigated different biological aspects of

the desert locust. The results of many of these studies are presented

by Uvarov (1928, 1966), Rao (1960) and summarized in the Locust hand-

book (1966).

There are three stages in the life history of the locust: egg,

hopper (nymph) and adult. However, differences in the bionomics of

the extreme forms of the locust do exist.

Bhatia and Singh (1964) indicated that the young adult males mature in ten days and the females in 13 days. The Locust handbook

(1966) mentioned that maturation may require two to four weeks under optimum conditions of weather and food. It may require up to six months however, during periods of drought or when abnormal low temperatures

prevail. The handbook stated that the process of maturation is tied to

the onset of the rainy season and is characterized by the disappear-

ance of the pink color in the hind tibia of the individual locust.

The adult's life (immature and mature adult) can last two and a half

to five months in the field to over a year in caged populations.

Uvarov (1966) noted that the process of maturation also depends on food quality, temperature and humidity. Norris (1952) reported that

the sexual maturity is roughly proportional to density of individuals.

The eggs are laid in an egg pod about 10 cm deep in the ground 190

(Locust handbook 1966). The egg pod may contain from 20 to 100 eggs.

Swarming individuals generally deposit 70 to 80eggs/pod in their first laying and the number declines during subsequentlaying periods

(Loucst handbook 1966). Ashall and Ellis (1962) reported, from East

Africa and Arabia, that 95-128 eggs/pod were producedby nonswarming individuals (solitarious) or their swarming progenies. The continuous swarming populations produced an average of less than 81eggs/pod.

Moisture and salinity of the soil, depth to the water table, temperature, vegetation, open site, topography and soil compactnesshave been reported to influence the individual female in her choiceof a suitable oviposition site (Popov 1958, Norris 1968, Bhatia andHarjai

1968, Hunter-Jones 1970a,b).

According to the Locust handbook (1966), the incubation periodof

the eggs varies from ten to 14 days in the summer breeding area of

West Africa to 25 to 30 days in the spring breeding area in North

Africa, but lasts longer in the winter/spring breeding zone. El

Miniawi (1965) reported that at temperatures of 24, 27, 30, 33 and

36°C. the mean duration of the incubation period lasted 27.6, 21,

16.2, 13 and 11.7 days, respectively. He concluded that the optimum

temperature to give the highest percentage of egg viabilityand hat-

ching was 27° 4- 3°C. Wardhaugh et al. (1969) found in Saudi Arabia,

that the incubation period ranged from 26 days at 24°C. to 12 days

at 37°C. in the field and laboratory populations(soil temperature).

With air temperature, the period averaged 20 days at 24°C. and12

days or above at 30°C. Hunter-Jones (1970a,b) reported, at constant 191 temperature, the duration of egg incubation ranged from 50days at

19.7°C. to 11 to 12 days at 35-41°C. He found the embryonic development of eggs was completed when they had experienced224 days-degrees above 15.1°C. He concluded that the optimum temperature for egg development was 26-36°C. and mortality increased progressively asthe

temperature decreased or increased. The hatching threshold is 19.2°C.

Water is necessary before egg development can take place(Shulov 1952,

Shulov and Pener 1963, Hunter-Jones 1970b).

Eggs hatch into a "vermiform larva" or what Dirsh(1974) called

the first real instar. The number of larval instars depends on the

physiological status of adult parents. Bhatia and Singh (1964) re-

ported that five to six and sometimes four to seven larval instars

are produced by the solitarious individuals,but in gregarious popu-

lations, there are five instars. They indicated that the developmental

period of the nymphs varies from 62 to 64 days at a constant temper-

ature of 24°C. but only 21 days at40°C. Wardhaugh et al.(1969)

reported that the nymphal period ranged from 25 days at adaily con-

stant temperature of 32°C. to 50 days at24°C. but only 21 days at 40°C.

Wardhaugh et al. (1969) reported that the nymphal period rangedfrom

25 days at a daily constant temperature of 32°C. to 50 days at24°C.

In Eastern Ethiopia, larval development lasted 38 days:five days for

the first instar, six days for the second instar, seven daysfor the

third instar, eight days for the fourth instar and 12 days forthe

fifth instar (Locust handbook 1966). In appearance, the nymphs look

like the adults except for their absence of wings, the disproportionate 192 size of the head to the body, and the rudimentary reproductive organs.

The passage from instar to instar is by moulting, whichinduces larval fasting several hours before and after the moult. The final moult produces the immature adult which is called a fledgling (Locust handbook 1966, Dirsh 1974, Bhatia and Singh 1964). Several different

ecological requirements affect the duration of the nymphal periodbut

the most important are: food quality, temperature, and humidity

(Uvarov 1966). Husain et al. (1964) reported that during each of the

five stages, the nymphs consume an average of six to eight timestheir

own weight. Albrecht (1962) indicated, in general, that hatchlings

of the gregarious forms survive better in a dry habitat than dohatch-

lings of solitarious individuals.

The duration of the life cycle is variable-as indicated above.

In Eastern Ethiopia, it was found that the period lasted 97days:

four days for eggs, 38 days for immatures and 45 days for immature

adults. The entire life cycle of an individual locust (egg to mature

adult) is 127 days (Locust handbook 1966).

Uvarov (1957) and Waloff (1966) reported that the desert locust

usually develops two generations annually in Western Africa. One

generation develops in the spring breeding zone which roughly occupies

the northern sector (e.g. North Mauritania). There the breeding occurs

during the first half of the year, from January to July. The second

generation is produced in the summer breeding zone,"approximately

between 15 and 18°N latitude" (Uvarov 1957, p.165). There the breed-

ing proceeds from July to October. The two areas lie nearly opposite 193 the Sahara, and are connected by the seasonal migration of the locust.

The breeding period in both areas corresponds to the rainy season, which is associated with the displacement of the Intertropical Con- vergence Zone (I.T.C.Z.) (Rainey 1963, F.A.O. 1968). Additional generations of the locust can also be produced as a result of erratic rainfall in the winter, near the Atlantic in Mauritania and the

Haggard Mountains, or as a result of an extended rainy season .(e.g. in the summer breeding zone). The above cycle pertains to the swarming populations but could also apply to solitarious populations (F.A.O.

1968).

Control strategies:

The biological background of locust control was reviewed by Gunn

(1960). Dempster (1963) provided a review of the different factors which affect the dynamics of locusts and grasshoppers.Uvarov (1957,

1961) stressed the diverse factors (man induced) which contributed to acridid problems in semi-arid and arid lands. In Western Africa,

Mallamaire and Roy (1959) reviewed the locust biology and control methods. The recent training in plant protection held in Dakar

(Senegal) emphasized various elements in the dynamics of the locust

(Popov 1975, Betts 1975). General control measures have also been reported by Uvarov (1928), Locust handbook (1966), Gunn (1975), Bhatia and Singh (1964). F.A.O. (1968) reported general control strategies and several elements of the desert locust dynamics.

The biological and morphological plasticity of locusts (Uvarov

1921) made Uvarov (1928, 1935) suggest that locust control should 194 involve international bodies. He also suggests (1954, p.137) defining economic status of locusts in terms of their "fluctuation in numbers, changes in the extent of the populated areas, qualitative differences between nonswarming and swarming populations". Haskell (1970) reported that locusts have no "passport" and Miss. Z. Waloff (1960, p.137) suggested that the

rational control strategies appear to require the readi- ness of most territories affected by the desert locust, to direct a large number of their control efforts to areas outside their boundries, and the creation of control units which could emulate the desert locust in their mobility.

Gunn (1975, p.148) reported that

at the present time, governments have the choice of providing what is needed in the confident expectations of preventing plagues, or providing too little or nothing which, will sooner or later, inevitably lay plague on their door steps.

The control of locusts generally involves international coordination, although local monitoring of populations is essential. Haskell

(1970) indicated that the Anti-locust Center in London has produced monthly summaries of the desert locust movements and their breeding since 1940. Since 1960, the Desert Locust Information Service spon- sored by F.A.O. has sent monthly information to approximately 40 different countries. In Continental Africa, several regional organizations exist and are primarily responsible for the locust control; they are: 0.C.L.A.L.A.V. - Organisation Commune de Lutte Antiacridienne et de Lutte Antriaviaire, in West Africa; the Desert Locust Control Or- ganization for East Africa - D.L.C.O/E.A.; and the North West Africa

Desert Locust Research and Control Coordination Subcommittee 195

(North Africa); other similar organizations exist in the Near East and

Southwest Asia (F.A.O. 1968).

Generally, control strategies involve, during plague periods, the systematic search and subsequent destruction of the locusts (swarms, hoppers, egg fields). During the recession period, the strategies shift to the survey of the locust populations in their breeding zones and to the continuous assessment of the quality and quantityof the populations (Roffey 1969, Popov 1975, F.A.O. 1968, Gunn 1960, 1975).

Methods of estimating locust populations are given by Rao (1942, 1960),

Ellis and Ashall (1962). These methods are discussed by Popov (1958,

1975), and are reviewed by Bennett and Symons (1972).

Several strategies have been reported to control locusts during plague periods. Maxwell-Darling (1948, p.414) considered the locust policy to involve: "1) control measures near the crops, 2) control measures in the desert to prevent the young hoppers frominvading the crops,

3) control measures everywhere breeding occurs, 4) control of outbreak areas". Gunn (1960, p.293) reported the following control strategies:

"1) area outbreak control, 2) frontier defense including defense in depth, 3) overall attack and 4) local defense of the crops". He sel-

ected the control strategy of "frontier defense and defense in depth" owing to the knowledge of the migratory routes of the locust and to

the fact there are no outbreak areas of the desert locust (as compared

to the African migratory locust, which has several outbreakareas).

However, Gunn (1975) and F.A.O. (1968) considered that the best strat-

egy involved preventing swarms of the locust to form. This involves

air and ground survey techniques and chemical methods to suppress 196

threatening locust populations before swarms break out and start a

wide spread plague. Roffey (1969) suggested the surveillance of the

breeding areas during the recession period, particularly where and

when there had been rainfall.

Agronomical and mechanical control:

There are many mechanical methods which can be utilized to con-

trol locusts during plague periods. Their efficiency depends on many

factors and generally the techniques are advocated inareas where

labor is free and abundant. Many of these techniques were listed and

described in Uvarov (1928) and Bhatia and Singh (1964). The methods

generally involve destruction of the eggs either by ploughingor

harrowing the egg fields, or flooding if water is available, andco-

llecting and destroying egg pods. During the hopper stage, the meth-

ods consist of crushing the hoppers by physical means; collecting

them in special machines and destroying them or burning the hoppers

by flame thrower. Another method which can provide some degree of

control when properly planned is digging ditchesor providing mech-

anical barriers in front of advancing hoppers to concentrate the in-

dividuals which can then be destroyed.

Land utilization and management could increase the potential

threat of the desert locust in arid and semi-arid lands (Uvarov 1957,

F.A.O. 1968). Grazing and cutting could modify the vegetation and its

composition which could create a vegetation mosaic or provideecotones which are potential habitats for the locusts. Shifting cultivation has also been reported to create new habitats for the locust, because 197 the locusts breed in marginal thinly cultivated landsadjoining fallows and wastelands (F.A.O. 1968). Large scale irrigation schemes in deserts could "involve the danger of making the life of thedesert locust less hazardous than it is at the present time"(Uvarov 1957,

p.168). The F.A.O. (1968) suggested that new irrigation projects

should be monitored in areas habitually inhabited by the locust.

These conclusions point to the danger of increasing the potential

threat of the locust in arid and semi-arid lands, particularlywith

poorly planned projects of land utilization and management.

Varietal resistance:

Varietal resistance of crops to locusts is poorly known. Many

authors have found, if given a choice, that the desert locust selects

its food plants. Husain et al.(1946) found among 200 plants (60

families) which were given to the locusts, that some were not eaten at

all, others eaten with great reluctance, and the remaining were con-

sidered food plants of the locusts. Bhatia and Sikka (1956) concluded

that some plants ordinarily not eaten by the locust may be completely

damaged when growing close to other plants still less edible. Other

observations on food preference of the locust are found in Williams

(1954) and Kennedy (1939). Host preference of the desert locust was

also listed by F.A.O. (1968). The review of Mulkern (1967) on grass-

hopper food selection, listed several substances known to be phago-

stimulants for the desert locust. The review of Thorsteinson (1960,

p.215) on host selection in phytophagous insects, related food plant

selection to insect resistance in plants, although, he stated that 198

"in the context of food plant selection behavior, only the "nonpreference" type of resistance is of concern, not the other two types,

"antibiosis" and "tolerance" recognized by Painter (1951)".

Painter (1951) and Bullen (1966) reported a group of native corn called "Bitter corn or Maiz amargo" in Argentina which possesses con-

siderable resistance to the attack by the locust, Schistocerca

cancellata = Schistocerca americana cancellata (Serv.), although the

cause of the resistance is unknown. Bullen (1966, p.153) indicated

it appears that the desert locust often avoids sorghum where there are alternative food plants. In the Sudan (Nuba Mountains), late maturing varieties locally known as "Kau" and "Kurgi" (probably Sorghum durra :var. maximum) were resistant to locust attacks.

He further added that the African migratory locust (Locusta migratoria

migratorioides (R.& F.) was observed to damage white grained sorghum

more than red grained sorghum in Chad during the lastinvasion of the

locust. In the U.S.A., it has been observed that sorghum is damaged

less than corn by grasshoppers. Local corn varieties are less suscep-

tible to damage than improved ones, and certain sorghum lines (Kaffir,

sorgo) are more resistant to grasshopper damage (Painter 1951, Pfadt

1971).

Biological control:

Several biotic agents affect populations of the desert locust

which led Pradhan (1965) to formulate his theory on locust periodicity,

largely based on biotic elements of the environment. A long list

of predators and parasites are known to affect the locust (Uvarov 1928,

Dempster 1963, Greathead 1963, 1966, Locust handbook 1966). 199

Among the generally reported parasites and predators of the

locusts are several species of the genus Scelio(Proctotrupoidea) which parasitize eggs of the solitarious populations. Stomorhina

lunata (Diptera, Calliphoridae) is an important egg predatorof

swarming locust populations and Trox procerus (Coleoptera, Scara-

beiodea: Trogidae) is an important egg predator in the summerbreed-

ing areas of West Africa. The parasites which attack post embryonic

stages (nymphs, adults) include, among others,Blaesoxipha spp

(Calliphoridae) and Symmictus costatus (Nemestrinidae), and the pre-

dators include various ants, mantids, arachnids and otherterrestrial

vertabrates and invertabrates. Birds are ranked among the important

predators, even if they are usually opportunists (Greathead 1966).

Ellis and Ashall (1962) reported that up to eight million locusts

were eaten by birds in 14 days in EasternAfrica and Arabia. Bhatia

and Gupta (1956) noted that in addition to being an important mor-

tality factor in locusts, birds can also indicate sources of water

supplies and can be an indicator of the location of locustpopulations.

These considerations, according to Bhatia and Gupta(1956) led to

regulations prohibiting killing, shooting or capturing useful birds

in the Punjab (India).

Quantitative assessment of the effect of biotic elements onthe

locust population is inadequate. The available information can be

found in Greathead (1966). He stated that the biotic factors could

hasten the decline of the population and could prevent or delay the

build up of outbreak, particularly in areas with semi-permanent 200 breeding sites. F.A.O. (1968) concluded that, at the present time there is no hope for achieving biological control (introduction of predators and parasites) of the desert locust.

Chemical control:

Chemical control is the main method used against locusts, particularly since the advent of aircraft, which are used to monitor locusts and to spray chemicals in the whole breeding areas of the locusts to prevent plague formation (Gunn 1960, 1975). The method is chiefly directed against the hoppers, since the adults are difficult to kill (Locust handbook 1966).

Bhatia and Singh (1964) reported that BHC dust applied at

25 kg/ha is the main method to control the locust in India. The strength of the chemical depends on the stage of the locusts: 2.5% for first and second instars, 5% for third instar and 10% for the fourth and fifth instars. They also indicated that 70 mg/ha technical Dieldrin was effective against all the immature stages. Malla- maire and Roy (1959) reported that 25% BHC dust in finely ground natural phosphate gave good control of newly hatched hoppers when applied from small bags.

The Locust handbook (1966) listed several insecticides which are used against the desert locust. It recommended that Dieldrin not be used on or near crops approaching harvest time. In cultivated areas, dusting and baiting with gamma BHC are suggested. The chemicals which appear to be generally in use in the Sahelian area (e.g. Mauritania,

Senegal, Mali) are BHC, Fenitrothion, Endosulfan, Malathion in areas 201

of cultivation, and Dieldrin in wild habitats of the locust (Sidia

Abdellah 1974, Singh 1974). There are also indications that plant

extracts such as Azadirachta indica (neem) leaves or kernels can act as deterrants to the desert locust (Bhatia andSingh 1964,

Baron 1972). 202

CONCLUSIONS

Insect pests of cereal crops have been identifiedfor both

Senegal and Mali and correspond to the major groups of pestsfound

in similar countries. These groups of pests correspond also to

the major insect pests of cereal crops of the Senegal RiverBasin.

However, the distribution, biology, taxonomy, dynamics andensuing

control strategies are still poorly known.

Presently, agriculture in the Senegal River Basin is mostly

traditional. Often, this farming system has been said to be protect-

ed from pest attacks due to the biological equilibrium reachedby

crops (Smith 1974, Glass 1975). In addition, several factors of the

systems (e.g. size of farm, diversified crops,undisturbed environment)

favor development of a pest management program based primarily upon

inexpensive methods of pest control (e.g. crop rotation,host-plant

resistance, crop residue destruction and host-free period)

(Sasser et al. 1972). This will require a thorough knowledge of the

biology and ecology of the pests. It will also require the education

of the farmers.

There has been no regularity in crop production in the Senegal

River Valley owing to vagaries of rainfall, variation in the Senegal

River hydrology and the low productivity of traditional farming.

Changes for better crop production are being implemented. They re-

quire regulation of the River's dynamics and introduction ofimproved

farming practices. What affect these changes will introduce in the 203 dynamics of the insect pest complex is not yet known. According to

Rivnay (1964, p.43) "there are no sufficient general records which enumerate the transformation of insect fauna in areas where such

[irrigation, flood] ecological changes have taken place". However, according to Uvarov (1964, p.159), "a radical reconstruction of the injurious fauna is observed whenever new crops and modern farming practices have been introduced into peasant farming". Nickel

(1973, p.139) concluded that pest problems have been more often intensified when agricultural systems are changed, and "unless effective solutions are found, pest problems will increase rather than decrease with intensification of agricultural systems aimed at high productivity".

The framework of agriculture systems consist of the physical and biological environment and regulates the dynamics of the pest complex.

The physical parameters of crop production (e.g. climate, soil, etc.) are customarily investigated, while the biological parameters (e.g. insect,pathogens) are seldomly given priority. Qualitative and quantitative surveys of the entomofauna are necessary during the planning and execution of agricultural programs. They could identify the native fauna and distinguish potential insect pests. This would also avoid entomological crisis, and in areas where ecological changes are planned, secure valuable biological information which would otherwise be lost. 204

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