Pests of Mubgbean and Their Control

N.S. Talekar Entomologist

Asian Vegetable Research and Development Center Shanhua, Tainan, Taiwan

1. Introduction

Mungbean, Vigna radiata (L.) Wilczek, is a major legume crop grown widely in south- and southeast Asia, mostly on small-scale family-owned farms. This low input, short duration crop is prized for its seeds, which are high in protein, easily digested, and consumed as food. It is an important source of dietary protein, especially in Indian Subcontinent where consumption of protein is very low. Because of its short duration, mungbean is easily adopted to multiple cropping system in the drier and wanner climates of lowland tropics and subtropics. Despite its short duration, large number of insect pests attack mungbean from soon after germination to harvest limiting the yield and some pests destroy seeds in storage (Table 1). Since mungbean is grown mainly in the tropical climates, insect pests play important role in the economic production of the crop.

The insect pests that attack mungbean can be classified based on their appearance in the field as it relates to the phenology of mungbean plant. They are thus: 1. stem feeders, 2. foliage feeders, 3. pod feeders, and 4. storage pests. This classification is convenient in judging the economic importance of the , especially their influence on seed yield, and in devising control measures. In this chapter, therefore, the pests will be discussed according to this chronological order.

The major stem feeders, especially in seedling stage are the agromyzid flies, so call beanflies, consisting of at least three species. In India the girdle beetle, Oberia brevis (Swedenbord), a major pest of , sometimes attack mungbean. Its damage, however, is minor and localized. Large number of foliage feeders belonging to orders and Coleoptera feed on the foliage of mungbean and several other related legumes. These include armyworms (Spodoptera exigua (Huebner), Spodoptera litura (F.)) hornwonn; (Agris convolvuli (L.)), cotton ( biguttula biguttula Nishida), Bihar hairy caterpillar (Spilosoma obliqua (Walker)), Epilachna spp. and flea beetles, grasshoppers etc. Most of these are highly polyphagous and feed on wide variety of legumes and non- legumes. Their damage to mungbean is highly localized and most case minor. However, two groups of insects, aphids especially black bean aphids, Aphis craccivora Koch, and thrips belonging to genus Megalurothrips are especially -10 1- damaging to mungbean and other related legumes They will be discussed here. Major pod feeders are the hemipteran bugs especially the'most widespread southern green stink bug, Nezara viridula L., and two species of lepidopterous podborer, the Maruca podborer, Maruca testulalis (Geyer) and Limabean podborer Tretsche. Although other species such as the tomato fruitworm, Helicoverpa armigera (Huebner), Asiatic cornborer, Ostrinia furnacalis (Guenee) and others attack mungbean and other legumes, these legumes are secondary or minor hosts of these pests. Information on these pests can be more easily obtained from study on other crops. The storage pests include species of bruchids belonging to genus Callosobruchus are primary pests of mungbean, especially on stored seeds. Their control is especially important to reduce avoidable losses. - 102-

Table 1. List of insect pests recorded on mungbean

Pest species Order: Familya Plant Reference parts attacked b

Acrocercops phaseospora Meyr. Lep: Gracillarridae L Vyas, 1978 Actinomorpha psittacina (Haan) Ort: Acrididae L Litsinger et al., 1978 Agris convolvuli L Lep: Sphingidae L Nayer et al. 1976 Alcidodes collaris Pasc Col: Curculionidae S Nair, 1975 Alcidodes fabrici F. Col: Curculionidae S Nair, 1975 Amsacta albistriga Walker Lep: Arctiidae L Anonymous, 1970 Amsacta lactinea (Cam) Lep: Arctiidae L Subba Rao et al., 1976 (= Estigmene lactinea) Lep: Arctiidae Amsacta roorei Butler Lep: Arctiidae L Lai, 1985 ephippias Meyr. Lep: Gelechidae L Fletcher, 1914 Anoplocnemis phasiana F. Hem: Coreidae P Nayer et al. 1976 Antricarsia irrolata Lep: Noctuidae L Nayer et al., 1976 Aphis craccivora Koch Hem: Aphididae L, S, F, P Nayer et al. 1976 Apion ampulum Fst. Col: Apionidae Subramaniam, 1959 Aulocophora similis Oliver Col: Chrysomelidae P Litsinger et al., 1978 Autographa nigrisigna Walker Lep: Noctuidae L Nair, 1975 Bemisia tabaci Gennadius Hem: Aleyrodidae L Nene, 1972 Bruchus phaseoli Gyllanhae Col: Bruchidae Sd Anonymous. 1970 Caliothrips indicus (Bagnall) Thy: Thripidae L, F Lal et al. 1981 Callosobruchus analis (F.) Col: Bruchidae Sd Raina, 1970 Callosobruchus chinensis (L.) Col: Bruchidae Sd Gujar & Yadava, 1978 Callosobruchus maculatus (F.) Col: Bruchidae Sd Nair, 1975 Catochrysops cnejus F. Lep: Lycaenidae F, P Litsinger et al., 1978a Ceococcus coffeaie Green Hem: Coccidae L, S Subba Rao et al. 1976 Ceratina binghanzi Ck1l. Hym: Apidae Nayer et al., 1976 Chauliops fallax Scott Hem: L, P Rawat and Sahu, 1968 ------103-

Pest species Order: Family Plant Reference parts attackedb

Chrotogonus trachypterus Blanch Ort: Acridiidae L, F, P Lal 1983 Chrysodeixis chalcites (Esper) Lep: Noctuidae L Litsinger et al., 1978a Clavigralla gibbosa (Spinola) Hem: Coreidae L, P Nayer et al. 1976 Colemania sphenarioides Bol. Ort: Acridiidae L, F, P Nair, 1975 Coptosoma cribaria F. Hem: Pentatomidae P Nayer et al. 1976 Cydia ptychora Meyr. Lep: P Lal et al. 1980 Cvrtozemia coqnata Marshall Col: Curculionidae L Pal, 1972 Diachrysia orichalcea (F.) Lep: Noctuidae L Babu et al., 1978 Empoasca biguttula Shiraki Hem: Jassidae L Litsinger et al., 1978a Empoasca kerri Pruthi Hem: Jassidae L Pruthi, 1940 Empoasca moti Prughi Hem: Jassidae L ' Chabra et al. 1981 Empoasca terminalis Distant Hem: Jassidae L Chabra et al. 1981 Epilachna philippinensis Dreke Col: Coccinelidae L Litsinger et al., 1978a Epilachna spp. Col: Coccinelidae L Lal et al., 1980 Etiella zinckenella Tretsche Lep: Pyticidae P Litsinger et al., 1978a Eublema hemirhoda Walker Lep: Noctuidae L Nayer et al., 1976 Euchrysops cnejus F. Lep: Lycaenidae P Nayer et al. 1976 Eucosma melanaula Meyr. Lep: Eucosmidae L Nayer et al. 1976 Euproctis scintillans (Walker) Lep: Lymantridae L Subba Rao et al., 1976 Gracillaria soyella V.D. Lep: Gracillariidae L Nair, 1975 Helicoverpa armigera Huebner Lep: Noctuidae L, P Nayer et al., 1976 coffearia Nietner Lep: Torticidae L Litsinger et al., 1978a

Lampides boeticus L. Lep: Lycaenidae P Nayer et al. 1976 Lamprosema indicata F. Lep: Pyralidae L Nair, 1975 Leucopholis irrorata (Chev.) Col: Scarabaeidae R Litsinger et al., 1978a Locusta migratoria malinensis (Meyer) Ort: Acrididae L Litsinger et al., 1978a Longitarsus manilensis Weise Col: Chrysomelidae L Litsinger et al., 1978a ------10 4-

Pest species Order: Family Plant Reference parts attackedb

Luperodes sp. Col: Chrysomelidae Lal et al., 1980 Madurasia obscurella Jacoby Col: Chrysomelidae L Menon & Saxena, 1970 Maruca testulalis (Geyer) Lep: Pyralidae F, P Nair, 1975 Megalurothrips distalis (Karny) Thy: Thripidae L, F Lal et al. 1981 Megalurothrips usitatus (Bagnall) Thy: Thripidae L, F Chang, 1992 Melanagromyza sojae (Zehntner) Dip: Agromyzidae S Chiang & Talekar, 1980 Mylabris pustulata Th. Col: Meloidae F Nayer et al., 1976 Myllocerus maculosus Desbr. Col: Curculionidae Srivastava et at., 1977 Mythimna separata (Walker) Lep: Noctuidae L Litsinger et at., 1978a Nacoleia vulgalis GN. Lep: Pyralidae Nair, 1975 Nezara viridula L. Hem: Pentatomidae P Nayer et a1.1976 Oberea brevis S. Col: Cyranbycidae S Nair, 1975 Ophiomyia centrosematis (de Meijere) Dip: Agromyzidae S Chiang & Talekar,1980 Ophiomyia phaseoli (Tryon) Dip: Agromyzidae S. Saxena, 1973 Ostrinia furnacalis (Guenee) Lep: Pyralidae S, P Talekar et at., 1991 Oxya velox F. (= O. chinensis Thumb.) Ort: Acridiidae L, F, P Singh & Singh 1977 Pachytychius mungonis Marshall Col: Curculionidae Fletcher 1917 Phaneropteraftrcifera Stal Ort; Tettigoniidae L Litsinger et at., 1978a Phytomyza horticola Gour Dip: Agromyzidae L Singh & Singh, 1978 Plusia chalcytis F. Lep: Noctuidae L Nair, 1975 Plusia daubei F. Lep: Noctuidae L Nair, 1975 Plusia peponis F. Lep: Noctuidae L Nair, 1975 Riptortus fiuscus F. Hem: Coreidae P Nayer et at., 1976 Riptortus linearis F. Hem: Coreidae P Nayer et al., 1976 Riptortus pedestris F. Hem: Coreidae P Nayer et al., 1976 Spilosoma oblique Walker Lep: Arctiidae L Nair, 1975 Spodoptera exigua (Huebner) Lep: Noctuidae L Singh & Singh, 1978 ------

Pest species Order: Fainilya Plant Reference parts attacked b

Spodoptera litura (F.) Lep: Noctuidae L Nair, 1975 Stonzopteryx subsecivella (Zeller) Lep: L Litsinger et al., 1978a Sylepta sabinusalis Walker Lep: Pyralidae L Litsinger et at., 1978a Taeniothrips longistylus Karny Thy: Thripidae L, F Litsinger et at., 1978a Tricentrus bicolor Dist. Hem: Membracidae L, F Nayer et al., 1976 Zaphanera publica (Singh) Hem: Alyrodidae L, P Nayer et at., 1976 a Order: families: Col = Coleoptera, Dip = Diptera, Hem = , Hym: , Lep = Lepidoptera, Ort = Orthoptera, Thy = Thysanoptera bPlant parts attacked: F = flowers, L = leaves, P = pods, R = roots, S = stem, Sd = seeds - 105-

2. Stem feeders

Beanflies

Three species of flies belonging to family Agromyzidae are important pests of mungbean and several other legumes throughout Asia. The species that attack mungbean are: Ophiomyia phaseoli (Tryon); Melanagromyza sojae (Zehntner) and Ophiomyia centrosematis (de Meijere). Their importance lies in the fact that I they attack plant soon after germination when it is most vulnerable to insect pest attack. If these pests are not controlled, at times the whole -crop can be destroyed or severely damaged requiring re-sowing of the crop. The nature of damage and seasonality of these agromyzids is similar. Therefore same control measures can combat all three pests. The biology, nature of damage and control measures are described in details in this section.

Ophiomyia phaseoli

Morphology and Identification

Identification of adults of O. phaseoli in the field difficult because they do not cause significant damage; they are agile and thus difficult to observe in the field and, to an inexperienced person, they can be easily confused with adults of other agromyzid species since at least two other species of agromyzids (Ophiomyia centrosematis and Melanagromyza sojae) that attack most economically important legumes simultaneously with O. phaseoli. Spencer (1973) gives details of morphology of adults of several agromyzids, including O. phaseoli. For practical purpose, therefore, it is much easier to identify O. phaseoli and other agromyzids by observing larvae and pupae especially anterior and posterior spiracles of these immature stages (Figure 1). Besides morphological differences, their feeding and oviposition sites within the host plants give a fairly accurate idea of their identity (Figure 2). These details are explained by Talekar (1990).

Ophiomyia phaseoli larva is a cortex feeder and pupates in the cortex mostly at root shoot junction. Sometimes pupae can be seen sticking under the membranous epidermis (Talekar, 1990). In all plants the oviposition takes place in unifoliate or early trifoliate leaves. A biotype of this insect in Indonesia lays eggs in cotyledons of soybean. Both larvae and pupae can be identified by observing their spiracles. In both stages anterior spiracles are small, with a circle of six minute bulbs. Posterior spiracles closely adjoin on the conical projections usually with about 10 minute bulbs. The puparium is pale yellow, straw colored or light brown. .' -106-

A closely related species, Ophiomyia spencerella (Greathead) cannot be easily distinguished from O. phaseoli in its larval or even adult stages. The posterior spiracles of larvae or pupae are identical in both species, except that immatures in O. spencerella have 9.9 ± 1.2 openings on an average as against 10

Ophiomyia phaseoli Ophiomyia centrosematis Melanagromyza sojae Larva Last instar

F a Anterior I a ;la vat *: sp irac l es

iC Posterior

s p iracles a;

Pupa : ;.

Anterior ae*.:...... *0*. . spiracles **::

Posterior spiracles

Figure 1. Morphological characters of immature stages of three important species of agromyzids attacking mungbean in Asian tropics. -107-

l

Figure 2. Location of ovipositional and larval feeding sites in soybean plant and morphological characters of three stem feeding agromyzids. Ms. = M. sojae, O.p. = O. phaseoli, 0.c. = O. centrosematis (Please note, O. phaseoli does not lay eggs in the cotyledons of mungbean) -10 8-

in O. phaseoli (Cn-eathead 1968). Such minute differences, however, are too difficult to utilize in quick identification of the insect in the field. The most prominent character that distinguishes O. spencerella from O. phaseoli is the shiny black pupae of the former as against pale yellow to brown of O. phaseoli and O. centrosematis, another cortex feeding agromyzid. The shiny black color of the pupae of O. spencerella can be seen even without removing the stein epidermis.

So far O. spencerella is confined to countries in East-Southeast Africa and Nigeria. This insect does not occur outside Africa.

Biology

Eggs

Fertilized females are most active on warm clear days. They are active flier and seek tender leaves on the host-plant for oviposition. Adults have distinct preference for younger legume hosts for oviposition and feeding. They tend to lay eggs during the morning hours on the upper side of the leaves, often near the midrib close to the petiole. The eggs are inserted between the epidermis and spongy parenchyma. In all legumes . 0. phaseoli lays eggs in leaves, especially the unifoliate leaves. However, a biotype of this species found in Indonesia oviposits in addition to unifoliate leaves, in cotyledons of soybean only. It does not lay eggs in cotyledons of other legumes.

The egg is oval, milky white, opaque or translucent measuring 0.30-0.39 mm long and 0.10 to 0.17 mm wide (Talekar, 1990): About 10 to 15 % of leaf punctures contain eggs; remaining punctures are made by adults to feed on plant sap oozing out from the puncture injury. Number of eggs per female vary considerably. In common bean (Phaseolus vulgaris), van der Goot (1930) found that a female, on an average, laid 94 eggs, with a range of 16 to 183 in her lifetime. Morgan (1938) found a single female laid a maximum of 314 eggs and that the average for 17 females was 99 eggs/fly. Burikam (1980) found a single female laid an average of 77 eggs in during her life time. Earlier Raros (1975) reported a mean of 1106 eggs laid by a single multimated female and 416 by unimated ones throughout her lifespan. Oviposition period lasts from 3-4 days after adult emergence and continues for 10-15 days (Morgan 1938). Incubation period of eggs varies 2 to 4 days depending upon temperature (Agarwal and Pandey, 1961, Singh, 1982; Taylor, 1958). -109-

Larvae

The egg hatches in its capsule at any time of the day. Ophiomyia phaseoli undergoes three larval instars. The newly hatched, pale, yellowish white first instar larva remains motionless for 1-2 hours before beginning feedings. The first instar feeds mainly in leaf blade tissue before entering mindrib eventually entering the stem. The first larval stadium lasts between 1.7 to 2 days with a mean of 1.9 days (Raros, 1975). Second instar larva initially still feeds inside midrib but soon enters petiole and usually molts into third instar at petiole stem junction. The duration of second instar lasts between 2 to 2.4 days (Raros, 1975; Burikam, 1980; Singh 1982). The third instar feeds voraciously in stem just beneath the epideimis. In young seedling the larval feeding can extend up to roots but in most ceases at just below soil surface. The duration of the third instar varies from 4.5 to 5.5 days with a mean of 4.7 days in common bean (Raros, 1975), 3 to 4 days (mean 3.33 day) in cowpea (Burikam, 1980). Before pupation, the fully grown larva ceases feeding for 6-10 hours, constructs a semicircular window in epidermis for escape of adult emerging from the pupae. The prepupal period lasts 1.5 to 2 hours. The freshly formed pupa becomes opaque. -110-

Pupa

The site of pupation varies depending upon the stage and condition of the host plant. During the seedling stage, pupation normally takes place beneath the epidermis of the stem, near the soil surface. In the later stages of the host plant, pupation can take place at the junction of the leaf lamina and petiole. In some instances, pupation is observed in the midrib of the leaflet (Raros, 1975; Burikam, 1980).

The pupa is barrel shaped (Figure 1). The cephalic end is somewhat pointed and the posterior end is slightly rounded. There are 12 visible segments. When newly emerged, it is yellow with a brownish tinge and distinctly darker r ends. The segments are well defined and the anterior and posterior spi acles are black. Shortly before the adult emergence, the color of the whole puparium becomes dark brown: Puparium measures between 2.02 to 2.30 mm long and 0.81 to 1.05 mm wide (Talekar, 1990).

Pupal period varies according to temperature. Ali-Nasr and Assem (1968) found that below 22°C, the pupation period ranged between 11 to 14 days with an average of 13 days. At 28°C, it shortened to 10 to 12 days with an average of 11 days, and at 32°C, the pupal period lasted 8 to 9 days with an average of 8 days. Morgan (1938) in New South Wales, Australia, observed similar influence of temperature under field condition. Pupal period was 2 to 3 weeks when eggs are laid in late April (autumn), 4 weeks when the eggs are laid early June (beginning of winter) and 9 to 10 days in warm summer weather. -111-

Adult

The fully developed imago emerges from the puparium via a transverse T shaped slit or a crack made by its ptilinum. Immediately after emerging the soft bodied and unpigmented imago remains motionless to allow the wings to unfold and exoskeleton to harden and darken. The adult fly attains a metallic black color in about an hour. The adult flies of 4 to 5 hours after its emergence from pupa. Agarwal and Pandey (1961) report an average measurement of flies to be 2.07 mm long and 4.97 mm wide, including wing expanse. They found female to be slightly bigger than male. van der Goot (1930) found that females are 1.88 to 2.16 mm long and 0.70 mm wide at the thorax, with a wing expanse of 4.45 mm. In males, the body is 1.60 to 1.84 mm long and 0.60 mm wide at the thorax, with a wing expanse of 3.80 mm.

Raros (1975) found that female adults live for 23 to 42 days and males 31 to 38 days under undefined laboratory condition. If no food is provided they die in 2=3 days. Burikam (1980) observed much shorter adult longevity; 7.13 ± 2.39 and 15.42 ± 3.78 days, respectively, for males and females under laboratory condition. Singh (1982) maintained three sets of newly emerged flies in the laboratory. The life span averaged 49 hours for starved flies, 94 hours for flies provided with water only and 212 hours for flies provided with glucose solution.

Adults feed on three general food sources; water droplets on the leaves, natural secretions of plants, and host plant sap exuding from feeding and ovipositional punctures made on the leaves by the females. Adults starts mating after an average pre-mating period of 18 hours (Raros, 1975). Copulation takes place only during day time. Copulation lasts from 4 to 94 minutes with an average of 18.5 minutes under laboratory conditions (Raros, 1975). van der Goot (1930) reports the duration of copulation to between 1 to 2 hours usually occurring on the upper surface of the leaves. Males and females mate several times during their life. -112-

Generations

In Java, Indonesia, van der Goot (1930) reported the maximum number of generations a year to be 14, while in the Philippines, Otanes (1916) and in Australia, Morgan (1938) found that there are 9 to 11 generations a year. In India, Agarwal and Pandey (1961) recorded 8 to 9 generations between July and following April and in Egypt, Abul-Nasr and Assem (1968) found 10-12 generation a year.

Five life table studies made by Yasuda (1982) revealed that in common bean (Phaseolus vulgaris) the differences in the initial number of eggs laid was not great among four or five observations, however, the total survival rate from eggs to adults was season dependent. The survival rate was much higher in summer (14-20%) than in winter (3 to 6%) or Spring (8%). The location of puparium within the host plant during different seasons appeared to cause this variation. In Summer, pupation takes place in the lower part of the stem or beneath the soil, in winter it occurs in the upper part. Such seasonal changes in the site of pupation affects the parasitism by pupal parasites (Pteromalids) and summer pupae practically escape parasitism.

Economic Impact

In tropical to subtropical Asia, O. phaseoli remains a destructive pest of most food legumes; common bean, cowpea, mungbean, blackgram, lima bean and soybean (at least in Indonesia). The nature of extent of O. phaseoli damage in different hosts varies from crop to crop and season to season. In general, however, plants are more heavily damaged in the seedling stage than when they are old. The consequences of insect attack in the seedling stage, if the plant survives, are manifested even in the older plants. In general, the yield loss during rainy season is much less than in the dry season. In Java, Indonesia, in 30 observations at Bogor, van der Goot (1930) found that up to 100% common bean plants were damaged with high plant mortality and yield loss. In Tanzania the yield loss ranges from 30 to 50% (Wallace, 1939, Walker, 1960, Swaine, 1968). In New South Wales, Australia, Morgan (1940) found it impossible to grow common bean, indicating thereby 100% plant damage and total yield loss if plants are not adequately protected. In Taiwan this pest causes 35% yield loss (Talekar 1990) in common bean and mungbean.

In Indonesia, a biotype of O. phaseoli attacks soybean. Whereas in rest of the world, O. phaseoli lays eggs in leaves in all host plants, in Indonesia, the biotype lays eggs in soybean cotyledons soon after these plant parts emerge above ground. Larvae, after initial feeding in cotyledons, enter stems and in most cases kill soybean plant. The extent of damage and subsequent yield loss - 113-

varies from season to season. In dry season (June to October ) van der Goot (1930) found the plant mortality to be 80% compared to 13% in wet season (November to April). Ophiomyla phaseoli_causes very little if any loss in soybean in rest of the world.

In cowpea, O. phaseoli damage varies from location to location. In Indonesia, although the damage can reach up to 100% of the plant population, the plant mortality is rare (van der Goot, 1930). In the Philippines, however, O. phaseoli infestation is high throughout the year, especially in the dry season when plant mortality can reach 60%. Those plants that survive the attack remain stunted and produce few or no pods (Otanes,- 1918). In Taiwan O. phaseoli damage reduces cowpea yield by 32% (AVRDC, 1985).

In mungbean (Vigna radiata), van der Goot (1930) reported 100% plant mortality due to O. phaseoli infestation in South Sumatra in dry season. Similar plant.,mortality was observed in Malaysia (Ooi 1973). In Taiwan yield loss of about 20% occurs in autumn planting (Talekar 1990). In peas (Pisum sativum) Kooner et al. (1977) report plant mortality of 40% and yield loss of roughly 50% in India. -114-

Nature of Damage

The most serious damage by adults occur when plants are at the unifoliate stage. The unifoliate leaves show a large number of feeding and oviposition punctures on the upper side with corresponding light yellow spots, especially on the basal portion of the leaf. The first and second trifoliate leaves show some egg holes, but leaves situated above this are practically undamaged. Larval feeding soon after hatching leads to numerous larval mines which are better seen w on the underside of the leaves just under the epidermis and appear silvery, curved stripes. On the upper side, only few tunnels are visible. Later, both egg holes and larval mines turn dark brown and are clearly visible. In case of severe attack, infested leaves become blotchy and later turn down. These leaves may dry out and even fall down. When infestation comes late (when plants are mature), insect damage is confined to the leaf petioles in which case this plant part gets swollen and, at times, the leaves may wilt.

The developing larvae in second and third instar mine downward into cortex just underneath the epidermis. Third instar continues to feed downwards into the tap root and returns to pupate still inside stem close to the soil surface. The feeding tunnels are clearly visible on the stems (Talekar, 1990). If insect population is high, larval feeding leads to destruction of cortex tissue around root-shoot junction. This initially leads to yellowing of leaves, stunting of plant growth and even plant mortality. If the damage is less severe, the root-shoot junction area appears swollen. In some cases plant produces adventitious roots above this swollen area on the stem.

In Indonesia, where a biotype of O. phaseoli attack soon after emergency, larval tunnels in cotyledons are clearly visible (Talekar, 1990). Later damaged cotyledons turn yellow and drop off. In most cases the plant is killed with 10-15 days after emergence.

Control Measures

Adequate control of O. phaseoli m tropical to subtropical Asia is necessary if one is to get satisfactory yields in most economically important legumes such as common bean, soybean (especially in Indonesia), mungbean, cowpea and peas. This is especially true when the crop is grown in dry season as is the case with most field legumes such as soybean and mungbean which are traditionally planted after wet-season rice crop. The fact that O. phaseoli infestation only in seedling stage causes economic yield loss, it is essential to w control this pest only during the first 4 to 5 weeks after germination. Since O. phaseoli adults are tiny and agile and its major damage is hidden inside the plant stem, it is important to adopt control measures such as spraying of the -11 5-

chemicals immediately after germination or protection of the crop by applying chemicals in soil simultaneously with sowing of the crop. It is, therefore, important to know the seasonality of the pest to undertake appropriate prophylactic control measures.

At present use of insecticides is the only control measure practiced by farmers. This is mainly because of the absence of other reliable control practices. Considerable research has been done on developing alternate and safer control measures but so far none of these measures have yielded practical control measures.

Host-plant resistance

Despite its versatility and potential, this approach has not yet been successfully utilized in O. phaseoli control. This is mainly because the insect is confined to tropical, and subtropical areas where research on host-plant resistance is virtually non-existent. Most of the significant research on this aspect in recent years has been carried out at the Asian Vegetable Research and Development Center (AVRDC), Taiwan. AVRDC has identified sources of resistance to O. phaseoli in common bean (Talekar, 1990), soybean (Talekar and Tengkano, 1993), mungbean (Chiang and Talekar, 1980) and cowpea (Talekar, 1990). At present breeding for resistance is actively pursued in common bean by International Center for Tropical Agriculture (CIAT), Cali, Colombia at its program in Afiica. However, no active breeding is pursued in other three crops. AVRDC has developed several mungbean breeding lines with moderate level of resistance to O. phaseoli (AVRDC, 1990). However, the yield and level of resistance in these lines needs further improvement.

Cultural control

Amongst various cultural practices occasionally attempted so far, only the use of rice straw and similar other plant straw mulch gives some control of only a biotype of O. phaseoli that attacks soybean in Indonesia (van der Goot, 1930). This biotype lays eggs in soybean cotyledons and second and third instar larvae feed in the stems of newly germinated plant which invariably results in plant mortality. The rice straw mulch covers the cotyledons making them inaccessible for oviposition. Insect then lays eggs in unifoliate leaves, however, by then plant has developed adequately and tolerates O. phaseoli damage although the yield could be reduced.

Similarly ridging of the crop reduce plant mortality caused by O. phaseoli I both in common bean and soybean (van der Goot, 1930). Ridging crop 2-3 weeks after germination helps to cover the adventitious roots which are produced by the O. phaseoli damaged plants and damaged area around root -11 6-

shoot junction. The soil support prevents lodging and improves survival of the damaged plants.

Intercropping with 60 crop plants belonging to 14 botanical families failed to protect common bean, soybean and mungbean in tests carried out in Taiwan (AVRDC, 1981a; 1981b).

Biological control

In practically all over tropical to subtropical Asia where O. phaseoli_is a serious pest, a large number of parasites are also present. However, these parasites do not seem to play any role in checking the bean fly population. In Indonesia, for examples, where this and other species of agromyzids are especially serious several species of parasites are known exists (van der Goot, 1930) for at least 70 years. However, agromyzids continue to cause unabated damage. This is particularly true for pest control within 4 weeks after crop germination when O. phaseoli is particularly devastating. In East Africa two major parasite species Opius phaseoli and Eucoilidea sp. are chief biotic factors affecting the population of O. phaseoli and a closely related agromyzid, 0. spencerella. However, sufficient agromyzids still survive to cause heavy infestations in subsequent generations of plants. In Hawaii where O. phaseoli was accidentally introduced in 1968, Opius phaseoli and Opius importatus were introduced in 1969 (Davis, 1971) specifically to control the newly introduced pest. Initial studies showed 100% parasitism of the agromyzid in Kauai and 25 to 83% on Maui islands. However, surveys conducted in 1973-74 revealed parasitism to ranges from 8.3 to 23.5% only. Ophiomyia phaseoli still remains a problem in Hawaii. The hidden nature of larval and pupal stages of O. phaseoli reduces the effectiveness of most natural enemies in controlling this pest.

Chemical control

Insecticides are relatively quick acting and give immediate results. Both preventive and early curative insecticide treatments show promise in controlling 0. phaseoli. However, due to concealed nature of larval feeding and damage, preventive measures have better chances of succeeding than curative. Talekar (1990) gives details of various chemical control measures from the earliest use of inorganics and botanicals to modern insecticides including latest insect growth regulars.

Pre-sowing application of commonly used systemic insecticides such as carbofuran, aldicarb, phorate to soil alongside of seeds helps protect young seedlings when they are most vulnerable to 0. phaseoli infestation. This treatment at the rate of 1 to 2 kg/ha can protect the crop through the vulnerable period of 4 weeks after germination only if the soil is acidic. In alkaline soil, - 117-

these chemicals breakdown rapidly and post-sowing application of chemical sprays 2 weeks after germination is essential to protect the crop through first 4 weeks. Coating of systemic chemical like carbofuran on seed before sowing also control O. phaseoli in cowpea and mungbean (IRRI, 1981).

Spraying of chemical insecticide at weekly interval starting soon after gemination through only first 4 weeks gives adequate control of 0.-phaseoli on a wide variety of crops. Among the chemicals that give consistent control are monocrotophos, omethoate and dimethoate. These chemicals are structurally closely related and there is strong possibility that an insect strain developing resistance to one will have cross resistance to others (Talekar, 1990). A newly introduced trisect growth regular, cyromazine, is effective against wide range of agromyzids. Neither neem extract nor Bacillus thuringiensis control O. phaseoli.

Integrated Control

At present only chemical control measure is effective at controlling O. phaseoli. Cultural control measure such as rice straw mulching is effective only in Indonesia that too on soybean which suffers damage from a specific biotype of O. phaseoli. Ridging plants provide some control, however, this method is too -laborious to be practical in commercial production of any legume. Despite availability of large number of parasites, their effectiveness is extremely limited. Potential exist for integration of only host-plant resistance and chemical control. Availability of even moderately resistant legume cultivar will cut down the use of chemical insecticides. Sources of resistance in major legumes are already available, however, there are no breeding programs to develop agromyzid resistant legumes. Until that happens, we may have to depend on chemical pesticides to protect legumes from O. phaseoli for commercial production.

Ophiomyia centrosematis

Morphology and Identification

The eggs of Ophiomyia centrosematis are laid in hypocotyl of plant just underneath the epidermis. The practically transparent eggs, on the average, are 0.413 ± 0.023 mm long and 0.163 + 0.025 mm wide.

Larvae have three instars. The first instar is practically transparent and the second and third instars are milky white. Larvae become opaque before pupation. The length of the cephalopharyngeal apparatus was 0.22 ± 0.03 mm in the first instar. 0.44 ± 0.02 mm in the second, and 0.64 ± 0.02 mm in the third (Talekar and Lee, 1988). There was thus linear increase in the length of cephalopharyngeal -118-

apparatus from first through the third instar.

The anterior spiracles are much longer than posterior ones (Figure 1). The distal end of the posterior spiracle is divided into three conical structures with one opening on each (Talekar, 1990). This feature is retained in pupae.

Initially pupa is light yellow, becoming golden yellow and dark yellow just before adult emergence. Pupae on average are 2.30 ± 0.10 mm long and 0.89 ± 0.07 mm wide and weigh 0.708 + 0.021 mg (Talekar and Lee, 1988).

Adult is a small, shinning black species. Spencer (1973) describes details of other morphological characters.

Biology

Egg

Ophiomyia centrosematis flies hover over soybean plant and alight on the foliage but descend to stem to lay eggs just underneath the epidermis in the stem below cotyledon (hypocotyl). The feeding puncture are absent on leaves but are made in hypocotyl. Oviposition starts on the third day after adult emergence from pupae and peaks on the seventh day (Talekar and Lee, 1988). During the oviposition period one female, on the average, lays 63.25 ± 13.68 (range 45-85) eggs. Most eggs are laid between 1100 to 1700 hours. Egg incubation lasts 44.0 ± 0.33 days at 25°C.

Larva

Larvae emerging from the eggs fed on cortex just underneath the stem epidermis. There are three instars (Talekar and Lee, 1988). The first instar larvae are practically transparent and second and third instar are milky white. The duration of the larval period at 28°C was 10.88 ± 1.89 days (range 9-14).

Pupa

Pupation takes place in stem cortex at the root shoot junction. Initially pupae are light yellow, becoming golden yellow and dark yellow just before adult emergence. Pupae are 2.30 ± 0.10 mm long and 0.89 ± 0.07 mm wide. The pupal period lasts on the average 11.03 ± 0.85 days; ranging 11-13 days (Talekar and Lee, 1988). Although O. centrosematis laid up to 13 eggs per plant, there were, on the average, only two pupae per plant. Insect apparently suffers from considerable mortality in egg and larval stage. -119-

Adult

Adult emergence from pupae takes place during day time. At 18-20°C the peak emergence occurs at 1100 to 1300 hours whereas at 28-32°C, it takes place between 0700 and 0900 hours (Talekar and Lee, 1988). Most matings occur between 0500 and 0800 hours. Males live for 15.35 ± 5.63 days (range 6-24) and females 12.45 ± 4.06 days (range 6-21) at 28±1°C. Pre-mating period lasts 2.5 days, pre-oviposition 3.5 days, and oviposition 12.2 ± 3.8 days at 28 ± 1°C.

Temperature influences the duration of the developmental stage. Within the range of 20 to 35°C, higher the temperature shorter were the egg incubation and duration of larval and pupal stage (Talekar and Lee, 1988).

Economic importance

Ophiomyia centrosematis is a minor pest of most legumes in Asia and Africa. Its damages at times go unnoticed in the presence of more dominant O. phaseoli. In Uttar Pradesh, India, however, O. centrosematis is a destructive pest of peas (Pisum sativum). Singh et al (1981) found that more than 95% of the damaged plants die when the crop is planted 1-8 October. Plant mortality is reduced in crop planted in November.

Nature of damage

Major damage comes from larval feeding inside stem cortex below cotyledons. As a result of the feeding the cortex tissue is destroyed. Frass is accumulated in this part. Upon opening larvae are found feeding in the tunnels. Pupae are found in the same layer but at root-shoot junction. In severe case of damage, plant looks wilted and eventually die. Adults make oviposition and feeding punctures in hypocotyl but these punctures are too small, barely seen by naked eye.

Control Measures

Because the seasonality and nature of damage of O. centrosematis is similar to more predominant than O. phaseoli, special control measures for O. centrosematis are rarely undertaken. In fact, except for damage to peas in India (Singh et al., 1981) there are no reports of control measures undertaken to combat O:--centrosematis. No attempts have been made to search for legume varieties resistant to this pest. Cultural control measures such as ridging and mulching used to combat O. phaseoli are likely to give control of O. centrosematis. The -120- i

i chemical insecticides used to combat O. phaseoli are likely to be effective against 0. centrosematis.

i Some parasites that attack Ophiomyia centrosematis are primary parasites of other, more important agromyzids such as Ophiomyia_phaseoli. All parasites 1 are native. They do not seem to be important in checking the pest population at the beginning of the season when host-plants are in seedling stage and when agromyzid infestation causes significant damage. No effort has been made to introduce any parasite specifically to control O. centrosematis.

Melanagromyza sojae

Morphology and Identification

The eggs which are laid in leaf tissue is whitish partly transparent and measures 0.34 ± 0.02 mm in length and 0.15 ± 0.01 mm in width (Lee, 19776, Wang, 1979).

i Young larva, found in the pith, is nearly colorless. The peculiar shape, size and nature of sclerotization of posterior spiracular bulbs can be used in identification of larvae of this species (Figure 1). The anterior spiracles are short, knob-like, with eight minute pores. Posterior spiracles are well separated and normally consist of six raised pores around a central truncated horn. These characters are retained in pupae.

The pupa is cylindrical, golden yellow, and measures 2.75 mm long and i 1.00 mm wide (Singh, 1982). Pupa is always located in the pith tunnel, often at the level of unifoliate leaves of younger plants and usually near the fly escape hole, as a dark depression. w Freshly emerged adults fly has moist crumpled wings and very faint i pigmentation on the abdomen and legs. Progressive darkening and hardening of the body wall and legs occurs for about 30 minutes during which time the wings also become smooth and dry. Soon the fly develops its metallic black color with a I metallic shiny abdomen. Antennae, legs, and bristles on head and thorax are all black. The wings are transparent. Females are larger and have tube-shaped abdomen. In females body length is 1.88 mm, width at thorax 0.70 mm, wing expanse 4.45 nun. In male body length is 1.60 mm, width at thorax 0.50 mm, and wing expanse 3.90 mm.

Spencer (1973) gives details of other morphological characters. -121-

Biology

Eggs

Eggs are always laid on the under side of the young leaves; unifoliate if the plant has only two leaves, or in fully opened trifoliate leaves at the basal part of leaf lamina, near the petiole. Numerous feeding punctures are made on the upper side of the leaves. The egg measures 0.34 ± 0.02 mm in length and 0.15 ± 0.01 mm in width (Wang, 1979). The egg is whitish, partly transparent. Usually one leaflet receives 1 or 2 eggs, however, that number may reach 5 or 6 depending upon adult population density. Eggs hatch commences in 2 days, peaks in 3 days n and can last up to 7 days after oviposition (Wang, 1979).

Larva

Immediately after emergence, the larva bur rows through the mesophyll tissue into the closest vein disappearing downwards in the leaf eventually tunneling through the petiole ending up in the stem. In the stem, larva burrows tunnel into the pith reaching root shoot junction. It burrows further into thickened tap root, turns around, and moves upward into the pith, thus widening the original tunnel. It gnaws through xylem and phloem tissues to the epidermis, making a hole to the outside, close it with debris and pupates in the stem (van der Goot, 1930).

The larva is nearly colorless and attracts very little attention when the stem is cut open for observation. Larva undergoes three instars. Singh (1982) reports duration of three instars at 32 ± 2°C and 70% RH as follows: first instar, 22 hours and 3 minutes, second instar 42 hours and 52 minutes and third instar 98 hours and 2 minutes. The total duration of larval stage was 7 days. Natural mortality of larvae is very high. Despite large number of eggs a maximum of only two larvae were found in van der Goofs (1930) study in Indonesia. Wang (1979) reports 62.1, 24.1 and 20% mortality of larvae in 1st, 2nd and 3rd instars, respectively.

Pupa

The pupa is cylindrical, golden yellow, and measures 2.75 mm long and 1.00 mm wide. Duration of the pupal period in the laboratory at 30 ± 2°C and 70% RH was 189 hours and 36 minutes (Singh, 1982). At average temperature of 27°C, the pupal stage lasts 6 to 9 days in June in northern Taiwan (Lee, 1976). In Indonesia, van der Goot (1930) reports a pupal period of 9 to 10 days.

Majority of pupae emerge into adults during the morning and early hours of the day. The total development time from egg to adult is 16 to 26 days with an average of 21 days, in lowland Indonesia. -122-

Adult

The freshly emerged fly has moist crumbled wings and very faint pigmentation on the abdomen and legs. Progressive darkening and hardening of the body wall and legs occurs for first 30 minutes, during which time the wings also become smooth and dry. Soon the fly develops its metallic black color and seeks soybean and other host plants. Melanagromyza sojae adults are weak fliers and their activity is strongly influenced by the weather. They feed on plant juices from egg and food holes made in the leaves by females, dew drops and similar other moist materials. Copulation occurs 3 to 5 days after adult emergence. The insect copulates only in the morning hours from 0700 to 1000 hours. Oviposition begins soon after copulation and lasts for 19 days (Wang, 1979). Eggs are laid in the leaves. Eggs are laid in the leaves. In Taiwan, the insect laid 171±115 eggs per female throughout its life. It laid 1 to 34 eggs per day, and 50% of eggs were laid within the first 9 days (Wang, 1979).

In laboratory, van der Goot (1930) found life-span of adult to be 15 to 36 days with an average of 23 days for females and 10 to 46 days with an average of 26 days for males. This life span, according to the same study, was longer than it is under field condition. In Taiwan Wang (1979) reports the life span of 6 to 19 days for adult flies. In India, Singh (1982) reports average life span of slightly more than 4 days at 30 ± 2°C and 70% RH. .

Economic Importance

Melanagromyza sojae is a pest of mainly soybean and to some extent mungbean and blackgram. In soybean, the insect infestation occurs in the unifoliate or early trifoliate leaf stage. By this time plants are well established and the insect infestation rarely results in plant mortality. Yield loss varies from location to location and plant growth stage when infestation occurs. Yield reduction .occurs only when the plant is damaged in seedling stage. The later the damage, lesser is the yield loss. In Taiwan, yield loss among 163 soybean varieties was 31% (AVRDC, 1981). In Shandong Province of China, there are reports ofM. _sojae causing plant mortality in soybean (Anonymous, 1978). The yield loss there amounts to about 70 to 90 kg seed yield/ha. In India, Bhattacharjee (1980) studied relationship between M. sojae infestation, plant height and yield loss in soybean. According to his calculations, this insect, if not controlled, can cause up to 80% yield loss. This pest probably cause significant yield loss in soybean in Indonesia. However, in most cases, if the crop is not protected, Ophionryia phaseoli causes severe damage before M sojae infestation begins. Hence no independent information is available on the extent of plant damage or yield loss by M. sojae in that country. -123-

Nature of damage

Melanagromyza sojae overwhelmingly prefers soybean. The adult flies lay eggs in unifoliate or early trifoliate leaves and major larval feeding occurs in pith of the stem. On outside there are no symptoms of infestation except some minute ovipositionlfeeding punctures at the base of leaf lamina. When stem is cut open, feeding tunnels with larvae and pupae are visible. In slightly older plants, two separate tunnels are often found. The one in the lower half is older and has developed a dark brown color. It originates in the stem roughly at the junction of the unifoliate leaves, and extends downwards up to the soil surface, indicating that the infestation occurred earlier, from the eggs laid in the unifoliate leaf The second tunnel starts just under the top the plant and extends downwards up to the first tunnel. Presuming that the plant at the unifoliate leaf escaped infestation, this tunnel can extend up to the soil surface. This feeding results from the later infestation of trifoliate leaves. If the plant is damaged very early, at times the later infesting larvae do not have enough pith tissue to feed on. Under such circumstances, the larva gnaws upwards resulting in the hallowing of the top which at times leads to weathering of the top.

Control Measures

In most legumes, the seasonality of occurrence of Melanagromyza_sojae is similar to more predominant agromyzid Ophiomyia phaseoli which infests host- plant at the same time or even earlier than M. sojae. In most cases, the control measures adopted for combating O. phaseoli also control M sojae. Since M. sojae prefers soybean over other host plants, the control measures described here are for the control of this pest on soybean.

Since M. sojae damage in seedling stage only causes economic yield loss, it is essential to control this pest only during first 4 to 5 weeks after plant germination. Since adult flies are too small and at times remain hidden in plant canopy and larval damage is hidden inside plant stem, it is important to adopt control measures such as spraying of chemicals immediately after crop germination or protect the crop by applying chemicals in soil simultaneously with sowing of seeds. It is important to know the season when the pest is serious to undertake appropriate prophylactic control measures. In general pest is more serious in dry season than in rainy wet season and precautionary control measures are more important in dry than in wet season.

At present farmers do not control or use only chemical control to combat M sojae. This is mainly because of the absence of other reliable control practices. Some research has been going on in soybean to devise other control r -124- i

measures but the progress in Asia, where this pest is more serious, is very slow. w Host-plant resistance

Chiang and Talekar (1980) found four wild Glycine soja accessions highly w resistant to M. sojae. The resistant accessions are viny plants with very thin stems. Breeding resistance into cultivated soybean failed because in order to have high yield, it was essential to have plants with thick and strong stems to support large number of pods without lodging. Any increase in stem size beyond the viny stern of the resistant parent increased the susceptibility of the progeny to M. sojae. Since despite 100% plant infestation yield loss is barely 30% and the fact that this pest rarely kills plants, it is possible to develop soybean cultivar tolerant to this pest. Some soybean accessions indeed show tolerance - no yield loss despite w heavy infestation - to M. sojae (AVRDC, 1979). i Biological control Although several species of parasites are present in areas such as Indonesia, India and Taiwan where M sojaeis endemic on soybean, their parasitism rarely exceeds 50%. Most of this parasitism comes rather late in the season after insect has attacked the plant and caused significant damage. During dry season in areas endemic to M. sojae the pest population is so high that enough insects escape parasitism and continue to cause serious crop damage. Most of the reported parasites are native and there is no introduction of any natural enemy anywhere t specifically to control M. sojae.

Chemical control

Preventive and curative insecticide application both have potential in giving t adequate. control of M. sojae. Since M. sojae damage in seedling stage causes yield loss, the earlier the chemical is applied, the better is its effectiveness. Among the more effective chemicals are monocrotophos, dimethoate, omethoate, w pyrazophos and cyaromazine. These chemicals must be spray applied once a week soon after germination to up to 4 or 5 weeks after germination. Systemic insecticides such as aldicarb, carbofuran and phorate applied in band along with seeds at sowing time gives satisfactory control for up to 2-3 weeks after germination. Talekar (1990) gives details of various chemical control measures I from the earliest use of inorganics and botanicals to modern synthetic organic chemicals including latest insect growth regulators some of which are specific to agromyzids.

w -125-

Integrated Control

At present only chemical control measures are effective in controlling M. sojae. Despite availability of large number of parasite, their utility in giving adequate control of M sojae is limited. Cultural control measures such as mulching which to some extent is effective in controlling Ophiomyia phaseoli was not control M sojae. Potential exists for integrated of host-plant resistance and chemical control to reduce the pesticide use. However, there is no breeding program in Asia where soybean cultivars resistant to M. sojae are being developed. -126-

3. Foliage Feeders

Among numerous insects that are reported to feed on foliage of mungbean in Asia (Table 1), only two groups, one species of aphid, Aphis craccivora Koch and three species of thrips: Megalurothrips usitatus (Bagnall), Megalurothrips distalis (Karny) and Caliothrips indicus Bagnall are specific to legumes and cause severe damage to mungbean. Most other species are not endemic on mungbean or related Vigna species. They are highly polyphagous feeding on wide variety plant species besides the members of Leguminoceae. Mungbean or related Vigna species are not their primary host. Tnformation on these pests can be gleaned from publications on pests of other economically important crops. In this section we will discuss the biology and control of A. craccivora and thrips.

Thrips

Three major species of Thysanoptera damage mungbean and other legumes in Asia. Megalurothrips dorsalis (Karny) and Caliothrips indicus Bagnall are prevalent in South Asia and Megalurothrips usitatus (Bagnall) mostly in Southeast Asia, although there are reports of M usitatus damage, albeit minor, in South Asia. Despite the taxonomic differences, the nature of damage in most Vigna host-plant species is similar and most control measures devised for one species work for the other species. Despite their importance on legumes in South Asia, there is very little, if at all, published information available on the biology, ecology and natural enemies of M. distalis and C. indicus. In this section, therefore, we will include the information on biology and ecology of M. usitatus but include information on control measures devised for all three species.

Biology of M. usitatus

Megalurothrips usitatus (Figure 1) is a damaging pest of adzuki bean, vegetable' soybean, grain soybean, and mungbean in Taiwan (Figure 1). Most of the biology and ecological research on this pest is done by scientists in Taiwan. The following description is based on publication of Chang (1987, 1988a, b, 1989, 1990a, b, 1992).

Megalurothrips usitatus has six distinct developmental stages: egg, larval I, larva II, prepupa, pupa, and adult. Eggs are laid in petals and sepals. This is the reason for occurrence of large number of larvae in coups in adzuki bean flowers. In laboratory, at constant temperatures between 14 and 30°C, the egg, larval, and pupal periods and adult longevity were 2-19, 5-10, 2-7, and 6-30 days, respectively. Female longevity is greater than that of the male at all temperatures. All M. usitatus died after hatching at upper (30°C) and lower 427-

Figure 1. Adults ofMegalurotrips usitatus. Top, male; bottom, female.

(14°C) temperatures. The mature larvae crawl downward and pupate 1-6 cm below the soil surface. Adults emerged in about 5 days. During vegetative stage, M usitatus is found inside the top, unopened, trifoliate leaves. During reproductive stage when plants start bearing flowers, more thrips are found in flowers on the 7th and 8th node on main stem of soybean plant. Within the flowers, male and female thrips were randomly distributed in the initial blooming stage (Chang, 1992). Rainfall adversely affects the survival of M usitatus. The water drops accumulated in the flowers and vegetative buds drowns and kill the .thrips. This pest, therefore, is not important during rainy ;season but can be devastating during dry season. -128-

Nature of Damage

Both larvae and adults prefer flowers over the leaves of adzuki beans. In flowers, both larvae and adults feed on pollen and rasp other flower parts and suck the plant juice oozing out from the injured plant parts. As a result of this type of damage, flowers drop of and no pods are formed (Figure 2). In mungbean plants can form new flowers but they are also attacked and at times there is total yield loss. In the absence of flowers, M. "'snafus feed inside

Figure 2. Severe trips damage in mungbean results in loss of flowers and plants do not produce any pods.

vegetative buds, rasping the unopened leave and sucking plant juice oozing out of the plant part. When the leaves open they all appear crinkled giving appearance of virus damage.

w -129-

Control Measures

Biological control

A minute parasitic wasp, Ceranisus menes was first observed on M. usitatus in adzuki bean field in 1988 in Taiwan (Chang, 1990a). It has occasionally being observed in laboratory from thrips collected in the field and reared in laboratory. This parasite attacks larvae and emerges before or during pupation of the thrips. In the Philippines, substantial predation of M usitatus was observed in potato. The most important predators were a myrid, Campylomma livida and a spider Argurodessp sp. In Japan Ceranisus femoratus and C. vinctus attack M. usitatus larvae. No information of worthwhile mention on the biological control of M distalis and Caliothrips indicus which attack mungbean in South Asia where publications after publications describe wasteful research on insecticide screening.

Cultural control

In study in Taiwan in adzuki bean field, in winter season, efficiency of blue PVC plate traps coated with sticky substance attracted significantly more M. usitatus than yellow or green traps (Chang 1990b). In spring blue trap also attracted more thrips than white, yellow or green. However, when the population increased, there was no difference in the number of thrips being attracted to blue and white traps. Megalurothrips usitatus was strongly attracted to light with wavelength of 450-480 nm. Potential exist to use these traps for reducing M usitatus damage to legumes grown at least on small scale farms.

Host-plant resistance

In India, in the first of two field tests, Chhabra and Malik (1992) screened 70 entries of mungbean germplasm for resistance to M. distalis. Deformity of inflorescence due to thrips damage was used as a criterion for resistance. On two resistant genotypes, SML77 and UPM82-4, insect development was prolonged and adult longevity was shortened. In the second test in which 20 genotypes of mungbean were tested, SML99 and SML100 were the most resistant and SML117 was the most susceptible to pest damage (Chhabra and Kooner, 1994). i -130-

Chemical control

Chemical insecticides are widely used to control thrips on mungbean and other legumes. Chang (1991) found that none of the chemicals he used control M. usitatus in Taiwan. In India several insecticides were tested for the control of M. distalis and C. indicus on various crops (Acharya and Koshiya, 1991; Singh and Singh, 1991; Ghorpade and Thakur, 1989; Koshta et al. 1988; Mundhe, 1980; Awate et al. 1978; Awate and Pokharkar, 1977; Gargav and Vaishampayan, 1978). Among large number of chemicals tested in these studies, spray application of dimethoate, monocrotophos, chlorpyrifos, quinalphos, and gamma- HCH (Lindane) gave satisfactory control of the pest. Soil incorporation of phorate, disulfoton, aldicarb and carbofuran at the time of planting also helped to reduce the thrips population.

Aphis craccivora

Aphis craccivora Koch is a polyphagous insect with marked preference to legumes. Amongst legumes, mungbean alongwith cowpea and groundnut are most damaged by this pest.

Biology

Adult aphids are black or dark brown, shiny, abdomen with large, dark, practically solid dorsal plate (Figure 3). Winged parthenogenetic females are 1.5 to 2.0 mm long, dark dorsal abdominal plate with cross markings of varying

Figure 3. Adult of Aphis craccivora.

number. Antennae are about two third as long as the body. w Nymphs are wingless, dark with I fairly rounded body 0 1 2 mm shape. Nymphs appear on the crop soon after germination from adults having overwintered or spent dry season on nearby w leguminous plants. In tropics only females, winged or wingless, are found, and - 13 1-

parthenogenetic reproduction occurs throughout the year. The aphid is ovoviviparous, with females retaining eggs inside their bodies and giving birth to small nymphs. Males are winged and sexual forms are occasionally found. The optimal development temperature is 24-28.5°C and relative humidity 65%. The optimal daylength for nymphal development is 16 hours light and 8 hours of darkness (Abdel Malek et al 1982). Photoperiod does not but plant chemistry, particularly reduction in the rate of translocation of photosynthates, influence formation of winged individuals (Mayeux, 1984). Aphis craccivora is capable of rapid population multiplication. On groundnut Talati and Butani (1980) observed that on groundnut offsprings from a single gravid adult aphid ranged 17 to 43 in 15 days. In the same laboratory study authors noted four nymphal- instars in A. craccivora when reared on cowpea. The total nymphal periods averaged 5.6, 5.1, 5.15, and 4.86 days in May-June, August-September, October-November, and March-April, respectively, in India. The duration of the total life-cycle during the corresponding periods were 11.07, 11.15, 10.79, and 10.42 days, respectively (Patel and Srivastava, 1989).

Aphis craccivora infestation of mungbean, cowpea or groundnut is serious only during cool-dry season. They do not survive periods of heavy rains. During drought, the pest survives on leguminous weeds. It can also withdraw into cracks in soil. As soon as the rains come and aphids are pushed out by closing cracks in soil, they colonize aerial plant parts. Aphis cracivora often migrates over wide distances into dry zones where, given transient periods of sufficient rainfall, it can cause damage, especially be transmitting viruses. During drought, irrigated plants are more heavily damaged than those that did not receive irrigation. Young colonies of nymphs concentrate on young shoots and are regularly visited by ants and there is mutualism between ants and aphids.

Nature of Damage

Young aphids cluster over tender shoots and occasionally young pods of mungbean and suck plant sap-from these plant parts. Heavy infestation weakens the plant and entire plant can be destroyed. Severe attack at the time of flowering and seed formation affects yield and produce infestation weakens the plant and entire plant can be destroyed. Severe attack at the time of flowering and seed formation affects yield and produce wilt symptoms. In addition, abnormalities due to virus diseases - rosetting, stunting, mosaic, mottle etc. - can be observed.

The greatest damage results from virus diseases which are transmitted by A. craccivora, especially in groundnut. Among the virus vectored by this aphid in various crops are: alfalfa mosaic, bean common mosaic, bean yellow mosaic, cowpea aphid-borne mosaic, cowpea banding mosaic, cowpea mild mottle, bean leaf roll and chickpea stunt virus. In mungbean, it transmits at least three viruses; green mosaic, leaf curl browning and little leaf (Benigno and Dolores 1978). -132-

Control Measures

Biological control

Most natural enemies of aphids are polyphagous attacking wide range of aphid species in a particular habitat. Therefore, important natural enemies attacking particular aphid species on crops tend to be different according to crop species and climate. This is especially true of aphid species such as A. craccivora, attacking a range of crop over large geographical areas. In addition, many natural enemies, especially parasitoids, are members of species complexes, morphologically very similar but with different host preferences and geographical distribution. Some of the important parasitoids of A. craccivora are: Thioxys indicus, Lysiphlebus fabarum and L. tesaceipes. Singh and Sinha (1983) found 9.4% parasitism by T. indicus shortly after appearance of A. craccivora on pigeonpea, in India. The peak rate of 64.6% was observed in later stages of infestation which was sufficient to suppress aphid populations on pigeonpea.

Important predators include coccinellid beetles, e.g. Cheilomenes sexmaculata and Coccinella septempunctata, neuropteran larvae, e.g. Micromus timidus and predatory diptera, e.g. Aphidoletes aphidimyza and a syrphid Ischiodon scutellaris. Use of chemical insecticides however, suppresses activity of all these beneficial . To conserve these natural enemies insecticides that are least toxic to predators and parasites that too only cases of absolute necessity.

Cultural control

Densely planted groundnut fields sown as soon as possible discourages colonization by aphids. Early sowing allow plants to start flowering before aphids appear, while dense sowing provide a barrier to aphids penetrating in from field edges. Sanitory measures are needed during the season and between seasons to prevent spread of viruses vectored by A. craccivora. Virus infected plants should be removed and any volunteer plants or weeds that could harbor viruses should be destroyed promptly. Insecticide applications were more effective in minimizing the incidence of A. craccivora when chickpeas were intercropped with barley or linseed (Prasad et al.. 1988). However, mungbean . cowpea or groundnut are not suitable crops for intercropping due to the risk of spread of the insect between these favorable host-plants. -133-

Host-plant resistance

Entomological research at IITA emphasizes breeding of cowpea cultivars resistant to aphids. Please read IITA's annual reports for the latest infolmation on aphid resistant cowpea. Potential exists for finding mungbean cultivars resistant to A. craccivora, however, due to uncertain incidence of A. craccivora in Taiwan, most of AVRDC's mungbean geimplasm has not being evaluated for resistance to aphids. Planting of aphid tolerant groundnut cultivars allows much retarded increased in small aphid colonies, at the same time predators arriving from wild plants can buildup populations and reduce aphid infestation effectively (Heinze 1977).:,...

Chemical control

Most major groups of insecticides, especially organophosphorus and carbamates, have been tested and some of them found effective against wide variety of aphid on economically important crops. Pirimicarb a selective aphicide is widely used to control various species of aphids. Other chemicals include acephate, dimethoate, endosulfan, menazon, and thiometon which have been recommended for aphid control. Other sprays found promising on crops include neem (Dimetry and El Hawary, 1995) and petroleum oil (El Sisi and El Hariry 1991). Cost of some of these sprays could, however, be prohibitive to subsistence farmers growing mungbean.

Integrated pest management

Potential exist for the integrated control of A. craccivora. Combinations of selective insecticides, predators and parasites, cultural methods and resistant cultivars has potential of controlling the pest on a sustainable basis. In groundnut, monitoring pest populations to time insecticide spray application is combined with the use of cultural methods and resistant cultivars (Mayeux 1984). In Bangladesh the IPM involving using malathion along with natural predation of Menochilus sexmaculatus was successful in controlling A. craccivora on beans (Ahmad and Sardar, 1994). - 134-

4. Pod Feeders

This group of pests include those that feed' externally on the pod at times devouring the pod, pierce their proboscis through the pod pericarp and such the contents of developing seeds, and bore inside the pod and feed on developing seeds while remaining concealed inside the pod. All these pests cause direct yield loss.

Some species of polyphagous hemipteran bugs belonging to families Pentatomidae and Coreidae pierce green. mungbean pods and suck juice from developing seeds. The species belonging to genus Nezara of the former family and genus Riptortus of the latter are especially destructive. Although these pests can feed on stems, inflorescence and even leaves, they prefer green pods and their damage to pods is economically more important.

There are at least four serious lepidopterous pests that bore into pods and feed on developing seeds. They include Maruca testulalis (Geyer) Ostrinia furnacalis (Guenee), Helicoverpa armigera (Huebner), and Etiella zinckenella (Treitschke). Some of these species are more serious at certain locations and in some cases their infestation levels vary from season to season. Not surprisingly, at times, all species can be present simultaneously, since the ecological conditions for their growth and development are similar. The nature of their damage to pods is not too different. The larvae of these insects bore inside the pods and feed on developing seeds, resulting in direct yield loss. i Nezara viridula i

Among several species of hemipteran bugs belonging to families Coreidae and Pentatomidae that damage mungbean pods, Nezara viridula (Figure 1), the commonly known as the southern green stink bug, is the most destructive, geographically widespread, and has the widest host range. One other species I Riptortus linearis is confined to South and Southeast Asia including Taiwan. Both species which attack mungbean are more serious on economically dominant soybean crop which appears to be their primary host. Most of the infolmation on biology, ecology and host-plant interaction is, therefore, generated with soybean as a host-plant and very little on other crops. The nature damage and control measures for both species are similar both on soybean and other legumes, including mungbean. Because of its greater economic importance, detailed infolination only N. viridula will be included with brief account of R. linearis. -135-

Biology

Nezara viridula adult starts laying eggs 18-25 days after becoming a full adult. The eggs are laid regularly in masses with oviposition lasting from 27-32 days with an average of 29.2 days. The females oviposit 4-6 egg masses (Singh 1973), with a normal egg mass consisting of 42-113 eggs.

I I l , 1 0 5 mm

Figure 1. Adults of Nezara viridula.

Egg incubation is 4-6 days, depending upon temperature. Singh (1973) found that the mean length of incubation for 103 masses containing 7019 eggs was 4.9 days, with cool temperatures during the months of December through February prolonging incubation by about a day.

The first instar nymphs are yellowish orange and slightly bigger than the eggs, shortly after emergence, they darken, remaining compactly clustered and motionless on the empty egg mass or adjacent to it. The first instar lasts 4-5 days during which the pest does not feed.

The second instar has a bright red on the head, large orange thorax, black abdomen and black eyes. It moves slightly away from the cluster andfeeds on green pods, although it-can feed on any part of the host plant. This stage lasts 3-4 days (Singh 1973). - 136-

The color, spots, and other markings remain essentially the same in the third instar, which lasts for 3-4 days (Singh 1973). The insects disperse considerably for feeding and settle to form small feeding aggregations.

The color pattern varies markedly during the fourth instar, which lasts 3-4 days. Individuals can be separated into light and dark, with the latter accounting for 10-15% of the population (Singh 1973). The nymphs begin to disperse.

The general outline of the body of the fifth instar nymph is the same as the fourth instar, but the developing wing pods become conspicuous and cover the basal portion of the abdomen. The aggregating behavior completely disappears by the fifth instar when nymphs become widely dispersed for feeding as well as resting. The fifth instar stage 5-7 days, the total length of nymphal stages varying from 18-28 days.

The adult is a large green bug. It has the shield-shaped form characteristic of a pentatomid, and it has the appearance typical of a stink bug. The female is larger than the male, and the males can be differentiated from females by a notch and two brown spots on the ventral surface. of the terminal end of the abdomen.

Several different color types, varieties or forms of this insect have been reported from tropical to subtropical Asia. At times they may have been confused for new species.

Riptortus linearis is widespread in tropical and subtropical Asia. Besides legumes, this species also feed on members of Solanaceae and Convolvulaceae. Eggs are laid in clusters of 3-5 mainly on the underside of the leaves and on pods (Kalshoven 1981). When newly laid, the eggs are gray, turning dark brown before hatching within 6-7 days. The nymphs undergo five instars in about 3 weeks in Indonesia and adult lives from 4 to 47 days. Both nymphs and adults feed on developing seeds within pods.

Nature of Damage

Although all stink bug species can feed on leaves and tender sterns, in general they prefer to feed on developing seeds within green pods. In soybean, while feeding stink bug injects histolytic agents into the seed, liquefying the content with the cells and causing cell wall to rupture. The insect then sucks the contents. -137-

When stink bugs feed on developing pods, the seeds do not develop and, at times, at least in soybean, pod drop occurs. The plant compensates for lost pods by setting new ones but these pods remain small. When harvested, the damaged seeds are shriveled and deteriorate rapidly in storage. In damaged seeds, germination is adversely affected. Stink bugs are also reported to transmit disease causing organisms in at least soybean seeds, which adversely affects germination of the seeds. It is not known whether this phenomenon occurs in mungbean and similar other legumes.

Control. Measures

Several factors including weather and natural enemies regulate population of stink bugs. Kiritani and Hokyo (1962) showed that more than 94% of N. viridula die before becoming adult. Mortality from egg to third instar nymph was 70-95%. Causal factors were stage-specific: parasites killed eggs, weather factors killed the first-instar nymphs, and predators killed second instar nymphs.

Biological control

In Japan two scelionid parasites, Asolcus mitsukurii and Telenonus makagawai, heavily infested eggs and were decisive in keeping the population of N. viridula from causing major losses (Kiritani and Hokyo, 1962; Hokyo and Kiritani, 1963). Kamal (1937) found that a proctotrapid egg parasite, Microphanurus megacephalus (Ashmead), was the only biotic agent preventing stink bug from becoming a pest in Egypt. In Hawaii, Trissolcus basalis (Wollaston) and Trichopoda pennipes var. pilipes F. prevent outbreaks of N viridula (Davis, 1961, 1967; Davis and Krauss, 1963), and in Java, Indonesia, two species, Ooencyrtus malayensis Ferr. and Telenomus sp. parasitize eggs of N viridula. In Malaysia, a reduvid bug, Sycanus collaris (F.), keeps N viridula under control, and in the Philippines, Corpuz (1969) found one hymenopterous parasite, Ooencyrtus sp, preying on the eggs of N. viridula. At AVRDC in Taiwan, we found another hymenopterous parasite, Trissolcus sp., preying on the eggs of R. linearis.

Since insecticide use for the control of stink bugs and most other pests infesting mungbean and related field legumes such as cowpea and soybean is still minimal compared to vegetables, use of these parasites may be the best means to control stink bugs. In fact, N viridula was successfully controlled in Hawaii by introduction of parasites from other countries (Davis, 1961, 1967, Davis and Krauss, 1963). Trissolcus basalis was imported from Australia and a tachinid, Trichopoda pennipes var. pilipes from the West Indies - the two species exerting enough pressure on N. viridula to eliminate serious outbreaks since 1963 (Singh, X973). -138-

Chemical control

Several chemicals have been screened and some recommended for the control of stink bugs. When synthetic organic insecticides were first introduced, organochlorines such as DDT gave satisfactory control. However, in later tests, DDT proved ineffective and all stages of N. viridula were reported to have developed resistance to DDT in Hawaii (Miyazaki and Sh6iman, 1966). Several organophosphorus insecticides and later carbamates such as carbaryl and mexacarbate also gave satisfactory control of stink bugs (Mitchell, 1965; Miyazaki and Sherman, 1966; Swaine, 1969). In a test in Taiwan, one synthetic pyrethroid, fenvalerate, gave good control of stink bugs and considerably reduced pod damage (AVRDC, 1982a).

Maruca testulalis

The Maruca podborer, Maruca testulalis (Geyer) (Figure 2) is a tropical insect attacking several species of food legumes in Asia, Africa, Central America, and South America. Within its wide host range, covering practically all economically important food legumes, Maruca feeds on practically all above- ground plant parts - young shoots, flower buds, stems, flowers, pods, and developing seeds. There are no reports so far of this insect feeding on leaves except when oviposition take place on leaves when newly hatched larvae may briefly feed on leaves before moving to feed inside flower or pod. Its damage to major plant parts severely affects the productivity of food legumes wherever the insect has achieved pest status. -139-

Figure 2. Maraca testulalis adult.

Biology

The biology and the nature of damage by Maruca podborer is similar in most Vigna species, especially between cowpea and mungbean, two of Maruca's economically important hosts. Since relatively more work is done on this pest with cowpea, most of the infoliiiation on the biology of this pest conies from studies on this legumes than on mungbean.

Eggs are mostly deposited on. flower buds and flowers of the legume host- plant. Jackai (1980) found 18.9 eggs on flower buds, 31.0 on flowers, 28.2 on abscission scars, 18.9 on peduncles, 2.6 on terminal shoots and 0.4 on pods of cowpea plants. Sporadic oviposition on leaves, leaf axils, terminal shoots, and pods has been . observed. Because of the erratic oviposition behavior during rearing Maruca podborer in laboratory, the reports of fecundity of this pest vary considerably: 8-140 eggs/female (Taylor 1967), 6-189 (Akinfewa 1975), 6 to 194 (Okeyo-Owuor and Ochieng 1981). Over 72% of the eggs in the latter study were fertile. In studies in India on three legume hosts; pigeonpea, cowpea and hyacinth bean, the fecundity varied between 35 to 38 eggs per female and 83% to 89% of the eggs were viable (Ramasubramanian and Sundara Babu 1989).

The roundish to slightly elongated oval eggs measure 0.65 x 0.45 mm. They are slightly yellow, translucent and have reticulate sculpturing on the thin and delicate chorion. The eggs are deposited in batches of 2 to 16 between the whorls of flower buds. Ramasubrainanian and Sundara Babu (1989) found insect to prefer hyacinth bean over cowpea or pigeonpea for oviposition. - 140-

The eggs hatch in about 2 to 3 days and the insect undergoes 5 larval instars during the total larvae period of 9 to 14 days depending upon host-plant species and temperature. The caterpillar is dull white with dark spots on each body segment, forming dorsal longitudinal rows (Figure 3). The mature

Figure 3. Maruca testulalis larva.

caterpillar is 16 mm long. Larva is a voracious feeder feeding mainly on flowers and green developing seeds inside the maturing pods.

The 2-week larval period is followed by 2 days of prepupal period during which feeding ceases completely and larva becomes pupa. The pupa is greenish or pale yellow initially darkens to a grayish-brown. Pupation takes place in a silken cocoon in the pod or more often in soil. Taylor (1978) describes the pupa, when pupation takes place in soil, as a double-walled pupal case consisting of an outer wall of silk, soil particles and other debris and an inner wall of loose strand of white silk woven in fishing net fashion and open at the anterior end. Pupation lasts 6 to 8 days and 68 to 76% pupae emerge into adults. (Ramsubramanian and Sundara Babu 1989).

The adult that emerges from pupa has light brown forewings with 3 distinct white spots. The hindwings are pearly white with distal brown markings. The wingspan measures 16 to 27 mm. In study in India with pigeonpea, cowpea and hyacinth beans, the adult longevity was 5.9 to 6.1 days for male and 8.5 to 10.0 days for female (Ramsubramanian and Sundara Babu 1989). Mating period lasted 1.6 to 2.7 days and total oviposition period 3.6 to 3.9 days. Sex ratio was 1:0.50 i to 1:0.84 in favor of females. The total life-cycle varies from 18 to 35 days depending upon temperature. -141-

Nature of damage

Flower buds, flowers, and pods are major plant parts attacked by Maruca pod-borer. Young larvae usually attack buds and flowers and older ones bore in maturing pods. The larva soon after emergence from egg starts feeding initially even on the leaves if oviposition has occurred on the foliage. In flower buds which usually harbors 1st or 2nd instar larvae, larva makes holes through the bud and feeds hidden inside. In open flowers all flower parts are damaged and excreta is accumulated in the flower. In most cases these flowers drop and do not bear any pod. The larval feeding in pods starts with small hole usually in proximal parts of the pod if the oviposition has occurred in the inflorescence. It feeds on the developing seeds moving from seed to seed concealed inside until it is ready for pupation.

In mungbean, invariably adjacent 2-3 pods are stuck together around area where insect has made entry hole in a pod. Sometimes, usually when the eggs are laid on leaves and if the leaf is in the proximity of a pod, larva sticks together part of the pod touching the leaf and makes hole in the pods be it distal or central part of the pod (Figure 4). We rarely find a larva boring inside a pod which is not touching to other pod or leaves. This indicates that a mungbean cultivar with pods not touching each other and radiates from well above the foliage so that the pods will not touch stem or foliage could be "resistant" to Maruca podborer.

■

Figure 4. Typical damage in mungbean by M. testulalis. Part of the pod touching a leaf is stuck together with the leaf and insect larva bores inside the pod. In the picture above the pod is turned slightly to expose the larvae. 42-

In Sesbania indica in Taiwan at least, insect lays eggs on leaves and larvae feed on foliage throughout the season. Newly emerged larva sticks several leaflets of compound leaves together and feeds concealed inside the leaf whorl. As a result of such feeding, the leaves are destroyed. Sometimes most of the foliage is covered with larval feeding leaf whorls and eventually the foliage is destroyed. Most mature larvae descend to ground and pupate in the top soil layer.

Maraca pod borer is a major biological limiting factor for cultivation of cowpea in Africa, especially West Africa and India (Taylor 1978, Saxena 1978). It is widespread in the Pacific and causes major damage to commonly grown legumes (Waterhouse and Norris 1987). No reliable data exists on the yield reduction in mungbean and other legumes because of the simultaneous presence of other pests that attack the crop. In Karel (1985) reported losses of 31% due to Maruca podborer in Tanzania. In India, Patel and Singh (1977) attributed 10% yield loss and Lalasangi (1988) report over 37% yield loss due to Maruca in cowpea.

Control Measures

Because of the hidden nature of larval stage, the damaging stage, and that of the pupal stage, it is difficult to control Maruca podborer by chemicals or other conventional means. Insecticides have been widely used in Asia, especially on yardlong bean where fresh pods are marketed as vegetables in Southeast Asia. However, due to very brief period soon after hatching before larvae enter buds or flower or pods, that the insect is exposed on the plant surface when insecticides can come easily in contact with the pest and kill it, chemicals have to be applied frequently. This is not always economical. However, due to the lack of suitable alternative control measures, vegetable farmers keep on spraying yard-long bean. This kind of pesticide use has to decrease.

In field crops like mungbean and cowpea, insecticide use is much less due to relatively shorted post-flowering period, compared to yardlong bean, when the insect is especially active. However, the damage by the pest in these crops is unabated.

Biological control

Large number of parasites have been reported to feed on Maruca larvae and some on pupae (Waterhouse and Norris 1987). However, in variably in all cases the extent of parasitism is low. Don Pedro (1983) found Phanerotonia sp. and sp. to be the most important parasitoids in Nigeria. However, their parasitism did not exceed 7%. Okoye-Owuor et al. (1991) reported pest mortality of 40.7 and 35.6% due to parasitoids and pathogens at two sites in Kenya. They -143-

reported presence of seven parasitoids, two predators, one nematode, and several pathogens attacking Maraca. Antrocephalus sp. was the predominant parasitoids, however, observed parasitism contributed 3.25% and 3.8% at two sites. In India, Lalasangi (1988) recorded Bracon greeni and Apanteles taragamae on Maruca larvae. The latter parasite was recently found attacking Maruca larvae on Sesbania indica at AVRDC in Taiwan. A parasitism of up to 92% of larvae was observed in summer. This is the highest parasitism of Maruca by any parasitoid anywhere reported so far. AVRDC is now exploring utility of this braconid in controlling Maruca on mungbean, cowpea and yardlong bean.

Cultural control

At the International Center for Insect Physiology and Ecology in Kenya, has over the years found intercropping of sorghum and cowpea reduced borer damage to both crops, including Maruca damage to cowpea (ICIPE). Since Maruca attacks wide range of legumes, voluntary legume plants should be promptly destroyed to reduce the carry over of the pest into the next season.

Host-plant resistance

The entomological research at International Institute of Tropical Agriculture (IITA) in Ibadan, Nigeria, emphasizes breeding of cowpea cultivars resistant to Maruca. They have screened over 7000 cowpea accessions and entries with varying levels of resistance have been identified and used in their host-plant resistance breeding. New breeding lines carrying varying levels of resistance to Maruca have been developed and made available to interested scientists. Please check'IITA's annual reports for the latest information on this topic. At the Asian Vegetable Research and Development Center (AVRDC) in Taiwan, mungbean germplasm consisting of over 5000 accessions have been screened for resistance to Maruca during the past two years. Several least damaged accessions have been selected for further screenings to confirm the resistance. This is a continuing research at AVRDC. Please check AVRDC's Annual Reports for the latest information.

Chemical control

Insecticides have been widely used for the control of Maruca on yard-long bean which is an important vegetable all over Southeast Asia especially during hot wet season when other vegetables are in short supply. In most cases chemicals are applied weekly or more often prophylactically. A wide variety of chemicals, often in mixtures of two or more, are used irrespective of whether such use leads to any better control of the pest. This poses various health hazards to farmers and consumers in addition to contamination soil and eventually water due to run-off. This misuse of chemicals is unlikely to stop soon unless alternative safe control -144-

measures are developed. Availability of various formulation of neem which gives equal or better control of Maruca on cowpea (Ramasubramanian and Sundara Babu 1991, Jackai and Oyediran 1991) could .replace the more toxic presently used chemicals.

For Maruca on cowpea, several commonly used insecticides such as endosulfan, carbaryl, methomyl, monocrotophos have been found effective (Singh 1977, Lalasangi 1988). The first application should be made at least one week before flowering and continued at a weekly interval until three weeks after peak flowering. No such information exists on Maraca control in mungbean.

Etiella zinckenella

Morphology

The white oval eggs (0.6 mm long) are laid singly or in batches of 2-12 on young pods, calyx or leaf stalk. Towards the end of incubation period of 3-16 days, eggs turn pink. The first instar larvae are 1 mm long with yellowish bodies and black heads. They wriggle violently if their pod is opened and they are disturbed. There are five larval instars. Just before pupation larvae become green with dark pink stripes. Full-grown larvae are 15 mm long. Freshly formed pupae are light brown but progressively turn dark brown to black as the time for adults to emerge approaches. Male pupae are generally larger, 8.5 mm long, than female, 8.0 mm. Pupae can be found in soil 2-4 cm below the surface. Adult forewings are brownish gray with a white strip along the leading edge of narrow fore-wings (Figure 5). Hindwings are transparent to opaque with darker outer edges. Wing span is 24-27 mm. -:145-

e 5. Adult of E. zinckenella.

Similarity with other pests

An additional morphologically similar Etiella species, E. hobsoni (Butler) infests soybean in Indonesia. The nature of damage by both species is practically identical. Naito et al. (1986) gives details of distribution of both species in Indonesia. The minute morphological differences in egg, larvae, pupae and adults are described by Naito et al (1986). The only substantial difference that can be used in distinguishing both species is found in adults. The ground color of the forewing of E. hobsoni is dark brown or dark reddish brown, without a white coastal streak found in E. zinckenella. The antemedial transverse fasca in E. hobsoni is orange edged with metallic scale. In contrast, the forewing of E. zinckenella is variably colored from reddish brown to purplish gray, but not dark, and has white coastal streak. The antemedia transverse fasca is orange brown to orange red, frequently with gold iridescence.

When the adults fold their wings at rest, the antemedial bands of the forewings of the forewings of E. hobsoni seen as a straight transverse band across the wings, while those of E. zinckenella are not straight. Etiella hobsoni_is generally smaller than E. zinckenella; the length of the forewing of the foliner is 7.5 ? 0.6 mm, and that of the latter 8.7 ? 0.7 mm. -146-!

Biology

The white oval eggs (0.6 mm long) are laid singly or in batches of 2-12 on young pods, calyx or leaf stalks. A single female lays 60-200 eggs during her lifetime (Kobayashi, 1976). Incubation lasts 3-16 days, depending upon temperature. The first instar larvae are 1 mm long with yellowish body and black heads. These larvae spend about half an hour moving about on the pod; they then spin a small web, bore through pod pericarp covered by the web and begin feeding on the developing seeds. There are five larval instars. A number of larvae may enter pod, but cannibalism reduces them to one or two. If the food supply in one pod is inadequate, they migrate to another. The larvae wriggle violently if their pod is opened and they are disturbed. Just before pupation they become green with dark pink stripes. Larval development lasts 2G days.

Full-grown larvae are 15 mm long (Kobayashi, 1976) when they leave the pod to pupate in a cocoon in the soil, 2-4 cm below the surface (Figure 6). Pupation lasts for 1-9 weeks, depending on the temperature. After emergence, the live up to 20 days. They are brownish gray with white stripe along the leading edge of the narrow forewings. The wingspan is 24-27 mm (Hill 1975).

Figure 6. Eliella zinckenella pupa exposed from the cocoon in soil. -147-

Nature of damage

Pod injury in soybean by E. zinckenella is recognizable even when the larva is absent. Large pods are marked with brown spot where the larva has entered; as the larva within the pod develops, the buildup of faces causes soft rotten patches on the pod. Seeds are partially or entirely eaten, and considerable frass and silk are present. A large hole is evident where the larva has escaped to pupate in the soil. In cowpea, lentil and , blossom drop and some pod drop occurs due to very small larvae feeding on the blossom and young pods. Usually one or two larvae can be found in each pod.

Economic importance

Etiella zinckenella is a cosmopolitan pest with worldwide distribution (Qu and Kogan. 1984). It attacks cultivated legumes including cowpea, garden pea, limabean, mungbean, pigeon pea, common bean and soybean. Amongst all host plants, soybean is by far the most preferred. This insect seems to have biotypes in different parts of the world. For example, it is a serious pest of common bean (Phaseolus vulgaris) in the USA but does not attack soybean there despite huge area under .cultivation. In most of Southeast Asia, it is a threat to soybean but does not readily attack common bean. A sex pheromone blend which attracts European strain in Hungary (Toth et al., 1989) is not effective against Southeast Asian strain of the pest.

Damage to soybean in Southeast Asia is widespread. It damages about 10- 15% pods in Taiwan, however, in Indonesia, the damage can reach 80% of pods (Talekar 1987). In the Philippine's Iloilo Province where soybean is a new crop, E. zinckenella damaged . 57% of the pods even in insecticide-protected plots (Litsinger et al. 1978b). In Iran E. zinckenella causes yield loss in. soybean of about 40% in the Province Lorestan and adjacent areas (Parvin 1981). In India this pyralid infested 11.43 and 50.9% pods of lentils and peas, respectively. This resulted in yield loss of 10.6 and 23.9% respectively (Singh and Dhooria 1971). In Egypt, this pest is reported to cause 40% loss of yield in cowpea (COPR 1981). -148-

a Control measures

Biological control

Etiella zinckenella has wide host range and occurs in the tropics practically throughout year. It also has large number of parasites despite cryptic nature of the pest. This presents an opportunity for biological control of this pyralid. However, no effort has been made either to introduce the natural enemies where the pest problem is serious or inundative use of any parasite. Sustained efforts in pursuing this field of research would lead to considerable reduction in pest damage in countries like Indonesia where this pest is especially serious.

Sex pheromone

A four component sex pheromone has been identified for E. zinckenella in Hungary (Toth et al., 1989). However, this chemical is not effective in Southeast Asia, particularly in Taiwan (Toth et al., 1995). Development of a sex pheromone would aid in detecting onset of infestation of the pest especially in soybean where the damaged plant parts-pods-are hidden in plant canopy. However, much work needs to be done to develop the pheromone for southeast Asian strain of this pest.

Host-plant resistance

To date, little effort has been made to breed mungbean or soybean cultivars resistant to E. zinckenella although sources of resistance to this pest in soybean are available (Talekar and Lin, 1994). This is because of the lack of adequate research in host-plant resistance breeding in southeast Asia.

Chemical control

Being an internal feeder it is difficult to control E. zinckenella by conventional means such as insecticide application unless chemicals are sprayed frequently to kill the first instar larvae while they are still outside pod. The sprays should be directed towards pods, and this requirement presents a mechanical problem in soybeans, as the leaf canopy completely covers the pods. In green pods of other crops such as lima bean, snap bean which are sold as fresh pods such pesticide use is prohibitive for health hazards reason. Among 54 insecticide tested by Stone (1965) carbaryl and azinphos-methyl and mexacarbate gave satisfactory control of E. zinckenella_on lima bean. In Taiwan monocrotophos, triazophos, fenvalerate and quinalphos gave satisfactory control of E. zinckenella on soybean (AVRDC, 1982). Triazophos and carbaryl, however, can cause phytotoxicity in certain soybean cultivars. -149-

Integrated control

Since very little success has been achieved so far in controlling this pest by anything other than chemical control, no efforts have been made to develop IPM for this pest in Southeast Asia or elsewhere. Unless additional information is generated through sustained research in host-plant resistance, biological control and sex pheromone, chances of development of usable IPM to reduce pest damage are meager. - 150-

5. Storage Pests

Introduction

Among scores of species of bruchids — insects belonging to the coleopterous family Bruchidae — that infest food legumes in the tropics, three species. Callosobruchus chinensis (L.), C. nmaculatus (F.) and C. analis (F.), infest mungbean (Vigna radiata [L.] Wilczek) in the field and during storage. The foinier two species are native of Asia and Africa. Mungbean, cowpea and pigeonpea serve as their principal hosts. Callosobruchus analis, an Asian native, is now found to be a pest of cowpea in Africa (Southgate 1978). Due to the movement of grains via trade, these pests. especially the former two, are now found in all six continents where they attack a wide range of pulses. Although the bruchids, commonly called pulse beetles or cowpea weevils, attack mungbean in the field and storage. it is the infestation of grains during storage that results in the greatest loss. In this section, therefore, after a brief discussion of their identification and biology, a detailed account of the nature of their damage and measures to minimize storage losses incurred by them will be discussed.

Identification

Due to the lack of adequate published reports on the systemics of Bruchidae, there have been numerous misidentifications of the bruchid species in the past. However, two publications by Southgate (1958) and his colleagues (Southgate et al. 1957) have removed much of the confusion. Since certain old names are still being used in the literature, the synonymy of each of the three species that attack mungbean is summarized in Table 1 (Vazirani 1976). - 15 1-

Table 1. Synonymy of three bruchid species that infest mungbean.

Callosobruchus Callosobruchus Callosobruchus chinensis (L ) maculatus (F ) analis (F )

Curculio chinensis L. 1758 Bruchus maculatus F 1775 Bruchus analis F. 1781

Bruchus pectinicorus L. 1767 Bruchus quadrimaculatus F. 1792 Bruchus jekeli All. 1847

Bruchus rufus De Geer 1775 Bruchus ornatus Boh. 1829 Bruchus glaber All. 1847

Bruchus scutellaris F. 1792 Bruchus vicinus Gyllen. 1833 Callosobruchus analis

Southgate, Howe et

Brett.1957

Bruchus bistriatus F 1801 Bruchus ambiguus Gyllen. 1833

Bruchus barbicornis F 1801 Callosobruchus maculatus Pic 1913

Bruchus elegans Sturm. 1826

Bruchus chinensis Sch. 1833

Bruchus adustus Mots. 1874

Callosobruchus chinensis

Mukerji & Chatterji 1951

Source: Vazirani 1976.

Certain striking morphological characters which differ in these species. and which are useful in bruchid identification, are described below.

Observation of the morphological characters of the adults provides the easiest form of identification (Figure 1). The shapes of antennae and the hind femur are two common characters that are used to easily distinguish the three bruchid species. In C. chinensis males, the fourth through apical segments are pectinate to highly pectinate whereas in females these segments are serrate. In C. maculatus the antennae are slightly serrate from the fourth through apical segment and in C. analis antennae are wholly testaceous and not serrate. The hind femur in C. chinensis is ventrally bicarinate with a denticle situated on each carina near the apex. The outer tooth is blunt and the inner tooth is long and straight, and rounded at the tip. In C. maculatus the hind femur is ventrally bicarinate, with a large blunt tooth on the outer carina and a sharp tooth of similar size on the inner carina. Both - 1 52-

teeth are situated near the apex. In C. analis, the hind femur is usually ventrally bicarinate, with a large pointed tooth on the outer carina. The tooth on the inner carina is very minute or absent. Mukerji and Chatterjee (1951) give details of differences in the genital structures of various bruchid species.

Since larvae and pupae are always hidden, their identity require greater efforts. Vats (1974) and Begum et al. (1982) give details of distinguishing 1 characters of bruchid larvae (Figure 2) and these characters can be used in conjunction with those of the adult's to confirm the identity of each species. Wightman and Southgate (1982) provide very useful information on the distinguishing characters of eggs of nine bruchid species based on scanning electron microscopic (SEM) studies. Southgate et al. (1957) and Southgate (1958) should be referred to in order to confirm the identity of the species discussed in this paper.

Biology

Several studies, mainly in the Indian subcontinent, report on the biology of Callosobruchus on various pulses (Rahman et al. 1943, Arora and Pajni 1957, 1959, Rajak and Pandey 1965, Raina 1970). In general, the life cycle history of all three species follows a typical coleopterous insect. There is very little difference among the three species. Raina (1970) made a detailed comparative study of the biology of the three species reared on mungbean at 30°C and 70% relative humidity (RH), a condition considered ideal for the development of the three bruchid species. The following information is extracted largely from his results.

Mating and oviposition

Adults mate within an hour after emergence from the seed. Mating lasts 5 to 8 minutes in C. chinensis, 3 to 8 minutes in C. maculatus and 3 to 6 minutes in C. analis. Although the insects mated several times, only one mating is sufficient to ensure egg laying. Eggs are covered with a sticky substance which fastens the eggs to the seed surface (Southgate 1979). At the time of oviposition, C. chinensis and C. niaculatus deposit a chemical -153- LI

OWNSINIM4

Figure 1. Adults of three species of Callosobruchus. A and B; C. chinensis, C and D: C. maculatus, E and F: C. analis. (Source: Raina, 1970)

45 - 154-

Anteclypeus Labrum 1t1 1

0

Antenna

Figure 2. Clvpeus, labrum, and antennae of larvae of U C. rnaculatus, ® C. chinensis, and©C. analis (Source: Vats, 1974). The bar length is 0.1 mm.

46 455-

oviposition marker' on the seed surface which has an ovicidal and arrestant action (Oshima et al. 1973, Yamamoto and Honda 1977, Honda et al. 1978). This chemical, a mixture of fatty acids, triglycerides and hydrocarbons, prevents the hatching of more than one or two eggs per seed and helps regulate the pest population and maximize use of the food. Yamamoto (1976) suggests that this chemical can be used as a possible oviposition inhibitor to control the bruchids. Certain edible oils (see discussion under Control Measures) give a similar ovicidal effect.

Callosobruchus chinensis laid an average of 78 eggs over a period of eight days; C. maculatus laid 128 eggs and C. analis 96 eggs over a nine-day period. Howe and Currie (1964) reported a slightly different fecundity data of the three species but this could be due to the selection of different host, cowpea, in their study.

Usually one to three eggs are laid over an individual seed although as many as five eggs in a study at AVRDC (unpublished) and seven in Raina's (1970) study were found on a single mungbean seed, when some seeds were still without eggs. The number of eggs laid was significantly correlated to the seed size (r = +0.95) in one study at AVRDC (unpublished). The average incubation period was 3.5, 4 and 5 days, respectively, for the eggs of C. chinensis, C. maculatus and C. analis. Egg hatching for all three species ranged between 94% and 99%.

Larval stage

Soon after hatching the larva makes a hole in the seed coat, just underneath the spot where the egg is laid, and enters the kernel where it feeds concealed inside the seed. When the eggs are laid on the pods, as in the case of insect infestation in the field, the newly hatched larva makes a hole through the pod cover, enters the developing seed and feeds and pupates inside the developing seed. Before pupation bruchid larva gnaws a circular hole until-only a thin layer or 'window' of seed coat is left intact. The combined larval and pupal period was 18.8, 20 and 23.5 days for C. chinensis, C. maculatus, and C. analis, respectively (Raina 1970).

Adult Stage

Adults of all three bruchid species emerge by cutting open the 'window' in the seed testa. The entire development from egg to the adult stage takes an average of 22.3, 24 and 28.5, days respectively, for C. chinensis, C. maculatus and C. analis at 30°C and 70% RH (Raina 1970). A similar developmental time was observed by Atwal et al. (1968) in C. analis on mungbean under similar environmental conditions. There was no difference in developmental time and life span between male and female in all three species and the sex ratio was 6:5, 7:6 -156-

and 1:1 males to females, respectively, for C. chinensis, C. maculatus and C. analis. Callosobruchus chinensis males and females lived an average of 7.6 and 7.4 days, C. maculatus, 8.2 and 7.6 days, , and C. analis, 6.8 and 8.0 days, respectively. Developmental mortality from egg to the adult stage was 23% in C. chinensis, and only 9% for each of the remaining two species. Most of the mortality observed was in the egg and early larval instars.

Nature and Extent of Damage

Damage in the field

Although bruchids attack mungbean in the field, damage to seeds per se is only minor. However, when infested seeds are stored, the adults emerge and lay eggs on the neighboring seeds. This secondary infestation is much more damaging. Banto and Sanchez (1972) report from 7.8% to 9.9% seed infestation by C. chinensis at the time of harvest. Infested seeds harbored bruchid larvae of varying stages of development.

Damage during storage

Three aspects of bruchid damage are of particular importance: (i) the overall weight loss; (ii) changes in nutritional quality and presence of off-smelling by-products of insect infestation; and (iii) loss in seed viability.

Seed weight loss. Weight loss can be a direct consequence of bruchids feeding on the seed. It may also occur as a result of accelerated loss of moisture due to perforation by bruchids of the mungbean seed. Vimala and Pushpamma (1983a) found that the level of insect infestation, as assessed by insect count, kernel damage, frass content and weight loss, increased with the period of storage up to one year. The percentage of kernels damaged in mungbean increased from 0.53% at the beginning of storage to over 16% after one year of storage and weight loss from 0.32 % to 7.22 % o during the corresponding period. Gujar and Yadav (1978) report a weight loss of 55.6% to 73% in individual seeds damaged by a single C. maculatus and 30.2% to 55.7% by C. chinensis in one generation. Banto and Sanchez (1972) reported total destruction of seeds when newly harvested, infested mungbean seeds (9.9% seeds damaged) were stored for three months. Infested seeds were unfit for human consumption. - 157-

Seed quality changes. Loss or denaturation of proteins and vitamins reduce the nutritional quality of pulses. In addition, the presence of insect excrement, cast larval skins, pieces of insect chitin or dead insects can have an abrasive effect on the human alimentary canal.

Vimala and Pushpamma (1983a) found up to 45 dead/alive insects per 100 g mungbean seeds after one year storage when practically no insects were present at the initiation of storage. Mungbean seeds contained from 0.39% to 0.41% frass after one year storage when practically none existed at the initiation of storage. No significant changes occurred in the grain moisture content. Uric acid, a metabolic by-product of insects which is present in insect excrement, increased from barely detectable levels at the initiation of storage to up to 31.5 g/100 g mungbean seeds. The authors reported a significant positive correlation between the number of insects and the uric acid contents of rnungbean seeds. The uric acid content reached above safety level after eight months of storage and still remained above that level after one year of storage. Similarly, Singh et at (1982) observed that free fatty acids, reducing sugars and uric acid contents increased with the increase in infestation of C. chinensis during a five-month period in three mungbean cultivars. The uric acid content was considerably greater in mungbean than in black gram as was the bruchid infestation. Doharey et al. (1983) also observed an increase in free fatty acids and alcoholic acidity in mungbean during 120 days of storage due to C. chinensis and C. maculatus infestation. They also reported that C. chinensis infestation increased protein content from 22.15% to 47.14%, and C. maculatus infestation increased from 22.15% to 57.55%, whereas in the check it only increased to 32.34%. No explanation for this change in protein content is offered by the authors. However, this anomaly appears to be due to the use of an inappropriate analytical method to determine the protein concentration. Doharey et al. (1983) estimated protein by analyzing total nitrogen rather than protein nitrogen (see Gujar and Yadav 1978). Some of nitrogen they analyzed could have come from uric acid rather than protein.

Vimala and Pushpamma (1983b) found that the starch content of mungbean was decreased by 6.19% after one year of storage and certain changes were observed in the reducing and nonreducing sugars and digestibility of stored mungbean seeds. But whether this is due to bruchid infestation or a normal change during storage is unknown. Pingale et al. (1956) found a reduced concentration of thiamin in stored mungbean seed infested with C. chinensis. The reduction was I roughly in proportion to the amount of insect damage to the seed. In addition, insect damage increased fat acidity and caused slight denaturation of protein.

fU - 158-

Seed viability loss. Even slight feeding damage by bruchids to the embryo impairs germination. Such feeding on the cotyledon will not affect germination but the vigor of the young seedling will be reduced, as in cowpea, due to similar damage by Acanthoscelides obtectus (Say) (Chin 1980). In a study with three mungbean and two blackgram cultivars, Singh and Sharma (1982) observed a progressive increase in seed damage and a proportional decrease in seed geimination during a five-month storage period. In mungbean, the seeds damaged by C. maculatus varied from 42.53% to 57.77% and loss in seed germination from 47.53% to 70.60%. There was much less seed damage and less reduction in viability in black gram seeds. Significant differences were observed in seed damage and viability among both mungbean and blackgram cultivars. As the level of Callosobruchus infestation to mungbean seed kernels increased from 4.33% to 16.67%, the loss of viability increased from 16.23% to 28.90% (Vimala and Pushpa mna 1983c).

Control Measures

The nature and extent of bruchid damage described above .entails sound control practices in order to protect the harvest from the ravages of bruchids, especially during storage. Because of the primitive nature of the storage facilities in many of the villages where most of the mungbean crop is grown on small farms, the small volume of produce, and the fact that the grains are frequently used for consumption, the use of fumigants or other insecticides is impractical. For bruchid control, therefore, sound farming practices, good storage facilities, coupled with nonchemical control measures are necessary. These measures include, the drying of seeds before storage, use of bruchid resistant cultivars, nontoxic chemicals such as vegetable oils, sex pheromones, biological control, and as a last resort, the use of selective and safe chemicals.

Although several hymenopterous parasites have been reported to attack bruchids in the egg, larval and pupal stages, their impact on populations is insignificant. Their use in biological control of bruchids during storage is not practical.

Drying of Seeds

A seed moisture content of below 10% impairs normal activity and development of storage insects and at moisture levels below 9.5% certain of these pests do not even oviposit (Girish 1983). Besides, most insects die within 10 to 20 minutes at temperatures of from 55° to. 60°C. The tropical sun is helpful in heating and drying the grains, thus ridding the seeds of bruchid infestation. Yoshida and Gichuki (1983) found that when adzuki bean seeds are spread in the sun in a layer of 3 cm deep, 550C was reached in 1.5 hours and maintained for 4 hours and 40 minutes. With a layer of 1.5 cm deep, 55°C was reached within 30 -159-

minutes and maintained for 4 hours. Sun drying of the grains before storage will thus not only reduce the risk of insects from primary infestation in the field being carried into storage, the reduction in seed moisture will minimize reinfestation from secondary sources. Low seed moisture also prolongs the effectiveness of vegetable oil and insecticide treatments which might be used to protect the seeds from storage insects (Doharey et al. 1984, Talekar and Mookherjee 1969).

Resistant Cultivars

Cultivars resistant to bruchids are yet to be developed although considerable progress in this field has been made. Due to its low cost and ease in use, coupled with the limited utility of other methods, especially chemical control, the use of bruchid resistant mungbean cultivars has a considerable potential. Since bruchids can infest mungbean pods in the field, as well as seeds in storage, resistance either in the pod, seed or both is desirable.

Resistance in the field. Doria and Raros (1973) screened 66 mungbean cultivars for resistance to C. chinensis damage to the pods. None of the entries was resistant to oviposition but resistance to larval survival was evident in EG Glabrous, EG- MG-4, and EG-MG-7. Mungbean accessions UPCA 23, 25 and 325 had the least number of eggs and lowest larval survival.

At AVRDC, field, greenhouse and laboratory experiments on 525 Vigna accessions at AVRDC led to the identification of the two accessions with different modes of resistance to C. chinensis (Talekar and Lin, 1981). Accession VM 2011 was least damaged when insect infestation occur red via pods, whereas VM 2164 was highly resistant in seeds. Both accessions are V. mungo. Hairiness on the pod in the case of the former, and antibiosis in the latter, are believed to be the resistance mechanisms involved (Talekar and Lin, 1981, 1992). Interspecific crosses to incorporate bruchid resistance of VM 2164 into mungbean proved to be difficult (AVRDC 1988, Fernandez and Talekar 1990). Hence a breeding program utilizing these resistance sources was discontinued. Renewed screening of only mungbean germplasm resulted in identification of two mungbean accessions, V 2709 and V 2802, which have moderate to high levels of resistance to C. chinensis (AVRDC 1990). Accession V 2709 (PI25393),. also designated as LM501, is a land race from India and V 2802 (PI 25461) comes from the Philippines.

In a series of laboratory and greenhouse tests, characteristics of resistance in V 2709, V 2802 and VM 2164 were investigated (Talekar and Lin 1992). Oviposition and emergence of first generation adults of C. chinensis were significantly reduced in pods of V 2709 and V 2802, compared with the susceptible check VC 1973A (Table 2). Artificial seeds prepared from mixtures of varying quantities of powdered seeds of resistant and susceptible accessions "(Shade et al 1986) were then exposed to infestation by C. chinensis. As the -160-

concentration of resistant accessions in the artificial seeds increased, the number of C. chinensis adults emerging after feeding as larvae in such seeds decreased (Figure 1). Adults that emerged from the artificial seeds made from mixtures of resistant and susceptible accessions were significantly lighter than from artificial seeds made from the susceptible accession alone. These results suggest that antibiotic factors may be present in these resistant accessions.

Table 2. Bruchid infestation on pods of resistant and susceptible mungbean accessions.

Accession No. of No. of No. of adults eggs/pod adults/pod /10 seed locules

First flush V2709' 5.95+3.68 0 0 V2802 14.75+12.85 1.41+_2.73 1.48+2.65 VC1973A 44.30+26.47 25.79±6.41 29.12±6.84 LSD 5% 12.64 2.64 2.72 LSD 1% 16.93 3.55 3.64

Second flush

V2709 14.69_+2.47 0 0 V2802 24.45+7.64 0.87+0.45 1.03+0.55 VC1973A 74.68+24.37 25.31+9.14 30.09±9.59 LSD 5% 9.47 3.35 3.54 LSD 1% 12.72 4.51 4.75

Third flush

V2709 17.85 _+5.52 0 0 V2802 18.15+6.52 0.49_+0.41 0.66±0.58 VC1973A 25.80+4.58 14.32±4.18 19.36+5.81 LSD 5% 4.08 1.52 2.14 LSD 1% 5.47 2.04 2.87

Data are means (+SEM) of 15 replicates, one plant per replicate. -161-

V 2709

V 2802

VM 2164

0 25 - 50 75 100 % OF RESISTANT SEED IN SUSCEPTIBLE

Figure 3. Emergence of C. chinensis adults from artificial seeds of susceptible accession VC 1973A containing varying levels of seeds of resistant accessions V 2709, V 2802, VM 2164.

A V. sublobata accession TC1966 was found to have high levels of resistance to C. chinensis (AVRDC 1991). This species is cross-compatible with mungbean. Japanese researchers report vignatic acid, a cyclopeptide alkaloid, as one of the factors responsible for resistance of TC1966 to C. chinensis (Sugawara et al. 1996). This chemical did not show any cytotoxic effect on Chinese hamster ovarian tumor cells and some humor tumor cells, indicating thereby that a resistance cultivar bred from using TC 1966 as the resistant parent could be safe for human consumption. This accession along with V 2709 and V 2802 are now being used at AVRDC to breed bruchid resistant mungbean.

The agromyzid resistant V. glabrescens accession, V 1160, also shows antibiosis type resistance to C. chinensis (AVRDC 1990). -162-

Rajapakse et al. (1983) screened 11 mungbean cultivars for resistance to C. chinensis. Cultivars Uthong 1, H101 and CES 87 were relatively resistant as the number of insects emerging from the seeds of these cultivars were the least and C. chinensis required a longer period to develop from egg to adult in these cultivars. Epino and Morallo-Rejesus (1982) screened 60 mungbean accessions for resistance to C. chinensis in seeds. Based on the first generation bruchids that emerged, UPCA accessions 11 and 30 showed moderate to high levels of resistance. The seeds of resistant accessions adversely affected the survival, increased developmental time and reduced growth index and body weight.

Use of vegetable oils and plant products

The use of edible oils to protect stored grains, especially pulses, against insect pest damage is an ancient method of pest control in India. In addition tc edible oils, extracts and plant parts of certain readily available plants, such as neem (Azadirachta indica Adr. Juss.) have also been utilized in villages where storage facilities are poor. In light of the adverse effects of insecticides on the environment, these methods of pest control are now attracting greater attention and research input.

In studies at AVRDC, mixing of soybean or groundnut oil at the rate of 2 to 3 ml/100 g seeds gave mungbean considerable bruchid protection for up to two months. Neither treatment affected seed germination but prolonging groundnut oil treatment to five months reduced seed germination considerably (AVRDC 1976). In a similar study Varrna and Pandey (1978) utilized oils of coconut, mustard, groundnut, sesame and sunflower mixed with mungbean seeds at the rate of 0.3 g per 100 g (w/w) of seeds. Oviposition of C. maculatus was completely inhibited when coconut and mustard - oils were used; very few eggs were found on mungbean seeds when other oils were used. Development of the adult population was prevented for at least five months, and the viability of the treated seeds was . unaffected. Coconut oil was the most effective followed by mustard, groundnut and sesame. Pandey et al. (1981) used oils of cotton seed, rice bran and sal (Shorea robusta Gaertn. f.) at the rate of 0.3 to 0.5 g per 100 g of mungbean seeds. All three oils protected the seeds for five to six months. Neither rancidity nor free fat acidity increased significantly in the treated seeds, and there was no adverse effect on seed viability. Doharey et al. (1984) studied the utility of oils of coconut, groundnut, mustard, rice bran, safflower, sesame and taramira (Eruca saliva Mill.) in protecting mungbean seeds, adjusted to the moisture content of 9.6%, 10.8% and 12.8%, against C. chinensis and C. maculatus. A concentration of 1% oil (w/w) protected the seed from both species. A higher grain moisture of 12.8% significantly reduced the efficacy of safflower oil against both bruchid -163-

. species. In a separate study Sujatha and Punnaiaii (1985) found that mungbean seeds can be effectively protected from C. chinensis by treatment with the oils of sesame, cotton seed, oil palm or neem at concentrations of 0.25% and those of groundnut or coconut at 0.5%. Treatment with all the oils at 0.125% resulted in lower infestation than the control.

In a study on the mode of action of groundnut oil, Sharma and Srivastava (1984) found a 90% reduction in oviposition by the oil treatment. Bruchid eggs affixed on the oil-treated seeds had 90% of the eggs died within 48 h as a result of coagulation of protoplasmic contents in the embryo. h the remaining eggs, the inhibition of embryonic development could be observed up to a certain extent but the embryo died soon thereafter. - Singh et al. (1978), however, found that the groundnut oil treatment of cowpea seeds prevented the emergence of bruchid progeny from the seeds rather than affecting the oviposition or mortality of the bruchid adults. The oil entered the eggs of C. maculatus through the micropile and in 1- to 2-day-old eggs, protoplasmic movement stopped and the protoplasm coagulated. In 3- to 5-day-old eggs where the larvae are partially or fully folmed, larval death occurred within minutes of the entry of the oil.

Jotwani et al. (1968) mixed 0.5, I or 2 g of crushed neem seeds with 100 g of mungbean seeds and observed the damage by C. maculatus in storage over several months. At the end of eight months, only 9.8% of the seeds were damaged in 2.0 g, 11.9% in 1.0 g and 18.8% in 0.5 g neem treatments, whereas in the control 59 % seeds were infested by bruchids . In a second experiment, the authors found that treatment with up to 2.5 g crushed neem seed per 100 g mungbean seeds reduced the bruchid oviposition considerably over a period of four months. Neem apparently repelled the adults from laying eggs on the treated seeds. In similar experiments, Yadav (1985) applied 2 to 50 mg neem seed oil per 10 g mungbean seeds and confined adults of C. analis, C. chinensis or C. maculatus over the treated seeds. Treatment of 50 mg neem oil prevented oviposition of C. maculatus as against 40 mg in the remaining two species. Dosages of 30, 10 and 20 mg neem seed oil suppressed adult emergence in the three species, respectively. This was due to the toxic action of neem oil against the bruchid eggs (Yadav 1985). Rajasekaran and Kumaraswami (1985) obtained complete control of C. chinensis when extracts of karanj (Pongamia glabra Vent.) and neem were coated on mungbean seed at the rate of 0.6% v/v and 0.8% w/w, respectively. In a series of laboratory tests in India, Qadri (1985) showed that neem extract synergized the toxicity of custard apple (Anona sp.) extract, and garlic extract synergized the toxicity of oleoresin obtained from chrysanthemum, to C. chinensis. - 164-

In a series of experiments, scientists at USDA's Stored Products Insects Research and Development Laboratory found that oils of several fruits, extracts of black pepper (Piper nigrum L.), dill (Anethum graveolens L.), Chinese cinnamon ( cassia Nees ex Blume) are toxic to several insect pests including C. maculatus (Su et al. 1972, Su 1978, 1985a,1985b). Similarly, Chander and Ahmed (1983) obtained good protection of mungbean against C. maculatus by mixing the powders of rhizomes of Acorus calamus L. (1%) and Cucuma zedoaria (Christm.) Roscoe (5% ) and seeds of Carum roxburghianunr Benth. Pranata (1984) found turmeric (Curcuma longa L.) powder extract to be toxic to the adults of C. maculatus when the extract was mixed with mungbean seeds. In one case vapors of Acorus calamus extract showed chemosterilant effect on C. chinensis. Exposure of adult females to the vapors reduced fecundity and caused regression in the terminal follicle at the vitellarium (Bhaskar et al. 1976).

Attempts were made to contiol Callosobruchus chinensis (L.), with fishbean, Tephrosia vogelii (Hook, F.), foliage powder. Mungbean seeds were coated' with 1, 2 or 4 g fishbean leaf powder/kg seeds and stored in nylon nets bags at room temperature for one year. Seed samples withdrawn from the bags once every 2 weeks were exposed for 24 hours to bruchid adults and insect mortality, number of first generation adults emerged after 1 month, and percentage of seeds damaged were recorded throughout the year. All dosages of fishbean powder remained highly effective for up to 1 year when the test was discontinued (AVRDC 1997). At every observation mortality of insects confined over the seeds was practically 100%. Very few, if at all, first generation adults emerged from the seeds and damaged seeds rarely exceeded 2% when damage to untreated seed sometimes passed 70% seeds. Dried fishbean which is used by certain subsistence farmers in Africa to control insect pests and the foliage of which contains rotenone, therefore, is very useful in protecting mungbean seed from bruchid damage for up to three cropping seasons. The leaf powder coated mungbean seeds, however, cannot be used for human consumption until they are thoroughly washed to remove all residues of the foliage powder.

Sex pheromones

Utilization of sex pheromone chemicals represents the safest form of pest control. Although this approach has not been used in the control of any of the three bruchid species which attack mungbean, recent studies have pointed out the existence of sex pheromone in bruchids and their potential, especially for pest monitoring purposes. In a laboratory study at AVRDC (1976) which utilized virgin females and unmated males, blowing of air over virgin females placed in an olfactometer attracted large number of males towards the virgin females. One- to two-day-old females attracted a greater number of males than the older ones. The males showed characteristic excitatory behavioral response including rapid antennal movement and extension of wings. Similar observations were made for -165- .1

C. maculatus by Rup and Sharma (1978) and Qi and Burkholder (1982). The chemical properties of the sex pheromone isolated from C. chinensis have been described (Honda and Yamamoto 1977, Tanaka et al. 1982). The pheromone consists of a mixture of callosobruchusic acid [(E)-3, 7-dimethyl-2-octenedioic acid] and several hydrocarbons. Neither the acid nor the hydrocarbons are active alone, their effect is synergistic.

Burkholder and Ma (1985) give details of the use of pheromones for monitoring various storage pests. The presence of a single bruchid in a trap indicates initiation of infestation and at such time suitable treatments can be utilized to reduce further loss. Bruchid pheromones can be utilized in the field in a similar fashion to monitor primary infestation of bruchids.. The presence of bruchids in the pheromone-baited traps will indicate initiation of infestation of pods. At this time the whole crop can be sprayed with a suitable chemical to prevent further spread of the pest or the seeds from the infested field can be dried thoroughly to reduce grain moisture to below 9%. The heat of the drying will also kill the larvae, pupae and possibly adults inside the seeds and a reduced grain moisture level will considerably reduce the secondary infestation during storage.

Chemical control

The appropriate insecticide when used properly gives assured and immediate control of insect pest during storage as it does in the field. However, the use of insecticides to protect mungbean in storage has serious limitations on small farms. Firstly, the grains are stored for short duration, in most cases from season to season. During this period the seeds are often used for family consumption. Under such conditions mixing grains with insecticides, even of relatively low persistence, is not advisable. Secondly, the use of fumigants is not practical because of the small sized produce and special precaution and training required to handle fumigants. Also in most cases mungbeans, along with other grains, are stored in living quarters where the use of furigants poses hazards. Thirdly, mungbean is still a low priced low input crop and use of insecticides may be uneconomical. Under such circumstances alternative methods, such as use of vegetable oils, clean cultivation, storing seeds after thorough drying in a clean storage space, will assure protection from bruchid attack.

In community storage and large-scale commercial storage facilities, insecticides can be applied by mixing with seeds, spraying the surface of bulk storage or stacks and by fumigation to protect mungbeans from bruchids. - 166-

Insecticide dusts or sprays. Initially the storage space can be disinfected by spraying the area with suitable chemicals such as fenitrothion or chlorpyrifos 2 methyl at the rate of 1 g a.i./m (COPR 1981). Subsequent risk of reinfestation can be reduced by spraying the surfaces of loosely stored grains or bags at intervals of about eight weeks with the same chemicals. In the past mixing seeds with lindane or pyrethrum dusts was suggested to control bruchids. However, due to the availability of chemicals such as malathion, DDVP, fenitrothion, pirimiphos methyl, which are less toxic to mammals and less persistent than lindane but more persistent and cheaper than pyrethrum, use of lindane and pyrethrum are no longer recommended. These chemicals can be mixed at the rate of 5 ppm with grains meant for long storage. Among the synthetic pyrethroids Duguet and Wu (1986) applied deltamethrin at the rate of 0.75 and 1.00 ppm to artificially infested cowpea in storage. This treatment protected the grains against C. maculatus for up to six months, when pirimiphos methyl dust applied at the rate of 10 ppm was effective for only three months. In China spraying of mungbean seeds with deltamethrin plus piperonyl butoxide at the rate of 0.25, 0.50 and 1.00 ppm protected the seeds against C. chinensis for up to 228 days (Duguet and Wu 1986). Synthetic pyrethroids, which are as selective for their less toxic effect on mammals but higher toxicity to insects as natural pyrethrins, but which are more persistent than the natural pyrethrins, have promise in protecting mungbean seeds in storage. However, their dosages should be carefully chosen to give protection for only the intended length of storage so that it will not leave excessive residues.

Recently, Davis et al. (1984) found that exposure of adults of C. chinensis and C. maculatus to the dust of tricalcium phosphate, a commonly used fertilizer, causes complete mortality in 6 to 8 hours. When insects were exposed to the compound mixed with snapbean (Phaseolus vulgaris L.) seeds at 0.01% to 0.25% concentrations, the number of Fl adults of C. chinensis that emerged was greatly reduced. -Similar results were obtained when C. maculatus adults were exposed to cowpea seeds treated with tricalcium phosphate and, in fact, at doses of 0.1% and above no Fl adults emerged. Tricalcium phosphate is readily available and relatively inexpensive. However, its mode of action and possible health hazards associated with mixing with grain need further study before this treatment can be suggested to small-scale producers.

Fumigation. Like the above-described insecticide trea(inents, fumigation of mungbean is. practical only in large-scale storage facilities. The greatest advantage of fumigation is the property of the fumigant to penetrate through the layers of grain and reach the target insect. Fumigants also penetrate through the feeding holes and oviposition windows in the seed and kill the larvae and pupae which are not reached by conventional insecticide application. In addition fumigants are capable of penetrating cracks and crevices which might harbor insects from the previously infested grains. Fumigation treatment does not leave persistent toxic residues and treated grains can be utilized after one to two days of aeration. - 167-

Several fumigants have been tested for their effectiveness against bruchids infesting various legumes and a few have proved to be more effective than the others (Singh and Srivastava, 1980, 1983, Mundhe and Pandey 1980, El Sayed and Kamel 1978, Tsuruta and Tadauchi 1983, Abu and Muthu 1985, Sadomov 1984). The adult stage is the most susceptible and the pupal the most resistant to fumigant action. The species of the host food legume does affect the susceptibility but such influence is of minor significance. Among the fumigants tested, phosphine is the most effective and convenient to use, especially for small-scale storage. The chemical is available in convenient pellet or tablet forms. Quantities of mungbean can be packed into jute bags with polyethylene liners into which pellets or tablets are placed. The bags are then sealed and left for four to five days during which the phosphine gas penetrates through the layers of grains and kills the bruchids. Usually Ito 1.5 g tablet per cubic meter space is a suitable dose to achieve complete disinfestation. If kept sealed, the phosphine treatment will also prevent insect reinfestation. - 168-

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