Academic Journal of Entomology 7 (3): 88-101, 2014 ISSN 1995-8994 © IDOSI Publications, 2014 DOI: 10.5829/idosi.aje.2014.7.3.84258

Life Cycle of variegatus (: ) in the Areas of Equatorial Climate of Cameroon with Uni-and Bimodal Distribution of Rainfall

12Kekeunou Sévilor, Yetchom-Fondjo Agrippine, 4 Yana Wescancellas, 2Missoup Alain Didier, 33 Heumou Cyril, Yengek Frankline and 1 Prombo Christophe

1Zoology Laboratory, Faculty of Science, University of Yaoundé I, Cameroon 2Department of Biology, Faculty of Science, University of Douala, Cameroon 3Department of Biological Sciences, Higher Teacher Training College, University of Bamenda, Cameroon 4Department of Biological Sciences, Faculty of science, University of Bamenda, Cameroon

Abstract: The situation of the life cycle of is complex in the Guinean and forest zones and has given rise to some confusion in the interpretation of the phenology. In the view to form a clear picture of this phenology in the equatorial climate zones of Cameroon, we have determined the life cycle of Z. variegatus in two seasons climate and compared it to that of four seasons. Weekly captures (30 and 60 minutes) carried out from January 2011 to April 2014, in Ndop (grassfield zone with unimodal rainfall distribution), Douala (evergreen forest of coastal zone with unimodal rainfall distribution) and Yaoundé (semi-deciduous forest zone with bimodal rainfall distribution) showed that, Z. variegatus was more abundant in Ndop (44.93±8.29 individuals) than in Yaoundé (39.46±2.93 individuals) and Douala (31.98±4.37 individuals). In each site, Z. variegatus was present throughout the year in two univoltine populations, which had unequal abundance and duration. However, in Douala, while the two populations were clearly visible in the 60 minutes captures, the small population was less visible in the 30 minutes captures than that of 60 minutes. The abundance in each population varied according to the post-embryonic stage with an abundance of young larvae (stage 1-3 larvae). The type of life cycle of Z. variegatus is similar throughout the Equatorial climate zone of Cameroon.

Key words: Presence Abundance Phenology Forest Coastline Rainfall Variegated Grasshopper

INTRODUCTION conditions, although the number of larval stages varies from four to nine in the laboratory [5,6]. Stages 1-3 larvae The variegated grasshopper Zonocerus variegatus are gregarious and always move in groups in search of (Linnaeus, 1758), is a polyphagous pest of food food while stages 4-6 larvae and adults are solitaries [6]. crops, which is widely spread in Western and Central The life cycle of Z. variegatus varies in different Africa [1]. It feeds on about 318 plant , including regions of the insect’s range [4]. In the ‘Sahelian and a wide range of food crops such as [2]. In Sudanian’ zones where there is a single rainy season, one Cameroon, it is classified as the third insect pest after well-defined univoltine population of Z. variegatus, scales and borers [3]. It is primarily associated to forest present in one part of the year and mainly in the rainy regions, but extends into the Savannah, where it is season is noted [4]. In the Guinean and forest zones, the restricted to riverine habitats [4]. Z. variegatus generally life cycle is more complex. Here, the distribution of rainfall has seven post-embryonic stages under natural is unimodal or bimodal and the dry season is shorter. In

Corresponding Author: Sévilor Kekeunou, P.O. Box: 812 Yaoundé, Cameroon. Tel: +(237)75278164/94483162.

88 Acad. J. Entomol., 7 (3): 88-101, 2014 these areas, Z. variegatus may be distinguished (1) by rainy seasons. However, in the evergreen forest zones of the presence of a univoltine population (1 generation per Mayombe (Congo-Brazzaville) where the rainfall year) in the dry season or (2) by the presence of post- distribution is unimodal as in Douala and Ndop embryonic stages throughout the year, resulting from (Cameroon), Z. variegatus is present throughout the year (a) one bivoltine population (2 generations per year) or in one univoltine population [9]. (b) two seasonal univoltine populations [1]. This confuse The aim of this study was to determine the life cycle situation in the forest and Guinean areas might be linked of Z. variegatus in the equatorial climate with two seasons to the possible existence of discrete seasonal population of Cameroon and compare it to that of four seasons. in the natural area [4]. This work is done in the view to form a clear picture on In terms of climate and vegetation, Cameroon the life cycle of Z. variegatus in the equatorial climate summarizes the main conditions of the Z. variegatus zones of Cameroon. range. The North, from the Adamawa to the Far-North, is dominated by Sudano-Sahelian vegetation with a MATERIALS AND METHODS tropical climate type (beyond the sixth degree of north latitude) in which two climate conditions are observed Study Sites: The study was carried out in Ndop (North- (Sudanese and Sahelian types). The Sudanese type is West region), Douala (Coastline region) and Yaoundé characterized by high temperatures and scanty rainfall in (Centre region) (Cameroon). the savanna landscape. It has a seven month rainy season In Yaoundé (3°87’ N, 11°52’ E) (Mbankolo), the and a five months dry season. The Sahelian type is vegetation is a semi-deciduous forest of the humid forest characterized by high temperatures and erratic rainfall with zone of Southern Cameroon which is more degraded by vegetation which consists of steppes and flood plains human activities. The natural herbaceous grassfield is [10]. dominated by annual and perennial plant species. The equatorial area (extends from latitude 2° to 6° Atmospheric temperatures during the experimental period North), includes the coastal mangroves, evergreen ranged from 22 to 29°. Rainfall distribution is bimodal, with forests, semi-deciduous forest, degraded forests, forest- two unequal dry seasons and two unequal rainy savanna mosaic, montane, subalpine meadows and seasons. The short rainy season (March–June) is submontane scenery. This area is characterized by heavy followed by the short dry season (July–August) and then rainfall with constant and average temperatures; two the long rainy season (September–November) is followed types of climates are observed. The first is a classic by the long dry season (November–March) [10]. Guinean climate prevailing party on a hill and the In Ndop plains (05° 59’ 275’’ N, 12° 25’ 693’’ E), the South-Cameroon plateau with four seasons (bimodal natural herbaceous grass field is dominated by annual distribution of rainfall): two unequal rainy and two herbs (Asteraceae) and Ageratum unequal dry seasons. The second type with two seasons conyzoides (Asteraceae) with some annual and perennial (unimodal distribution of rainfall), is a Cameroon climate plant species. Atmospheric temperatures during the kind prevailing in the vicinity of Mount Cameroon, experimental period ranged from 25.7 to 29 °C. The extending to the mouth of the Sanaga and including the atmospheric humidity of the region was fairly constant West highlands. Rains abound in these parts of the (85 %). Annual rainfall is more than 1200 mm and the territory and last approximately nine months. distribution is unimodal, with two seasons. The rainy In the Logone and Mayo-Kebi Valleys (Sahelian and season runs from mid-March to mid-November and the Sudanian zones) of Northern Cameroon, Z. variegatus short dry season from mid-November to mid-March. shows one univoltine population observed between June Douala (04° 04’ 660’’ N,09° 47’ 078’’ E) (Logbessou), and September [7]. In the semi-deciduous zone of in the ever green forest zone, is more degraded by human Southern-Cameroon where rainfall distribution is bimodal, activity. The herbaceous vegetation is dominated by the grasshopper is present throughout the year in two Panicum maximum (Poaceae), Chromolaena odorata univoltine populations of unequal abundance and (Asteraceae) and Alchornea cordifolia (Euphorbiaceae), durations [8]. No data exist in the North-West and with some annual and perennial plant species. Coastline regions of Cameroon where the rainfall Atmospheric temperatures during the experimental period distribution is unimodal, with short dry and very long was so weak, nearly 27°C. The atmospheric humidity of

89 Acad. J. Entomol., 7 (3): 88-101, 2014 the region ranges from 75 to 95%. Annual rainfall is more 3 months); stage 2 larvae appeared by early-February and than 3 500 mm and the distribution is unimodal, with two disappeared by late-May (almost 4 months); stage 3 seasons. The rainy season runs from mid-March to larvae were observed from mid-February to early-July mid-October and the dry season runs from mid-October to (almost 4.5 months); stage 4 larvae appeared by late- mid-March. March and disappeared by mid-August (almost 5 months); stage 5 larvae were observed from late-April to Sampling Procedure: In Ndop, Douala (Logbessou) and early-September (almost 4.5 months); stage 6 larvae Yaoundé (Mbankolo), samples of Z. variegatus were appeared by late-May and disappeared by mid- collected in the natural vegetation through sweep-netting. September; adults were observed from mid-June to mid- In each site, we carried out regular collections and December (almost 6 months). The second annual observations once every 7 days from January to population appeared by mid-September and disappeared December 2011 in Yaoundé; from January 2012 to January by late-March (almost 6 months). The stage 1 larvae were 2013 in Ndop and from April 2013 to April 2014 in Douala. observed between mid-September and early-November The duration of each capture was 60 minutes in Yaoundé, (almost 2 months); stage 2 larvae appeared by late- 30 minutes in Ndop, 30 and 60 minutes in Douala September and disappeared by mid-December (almost 2.5 (Logbessou). One point of capture was carried out in months); stage 3 larvae appeared by late-October and Yaoundé and Ndop while two were carried out in Douala. disappeared by late-December (almost 2 months); stage 4 In Douala, the distance between the first point of capture larvae appeared by late-November and disappeared by (for 30 minutes capture) and the second (for 60 minutes mid-January (1.5-2 months); stage 5 larvae appeared by capture) came out with almost 1000 m. All the collections mid-December and disappeared by late-January (almost began from a fixed point and extended across the entire 1.5 months); stage 6 larvae were observed from mid- site. The collected individuals were kept in aerated bags January to late-February (almost 1.5 months) and adults and the individual numbers were counted by stage and were observed only in March (almost 1 month) (Fig. 2). sex in the field. Thereafter, they were released at the site In Ndop, the first annual population appeared by where they were collected. late-April and disappeared by early- December (about 7.5 months). In this population, the stage 1 larvae appeared Data Analysis: Figures 2-5 show the variation of the from late-April to mid-June (almost 2months); larvae of number of Zonocerus variegatus captured in 30 or 60 stage 2 appeared by early-May and disappeared by minutes, depending on the dates of catch at each site. mid-June (almost 1.5 months); larvae of stage 3 appeared Because a 30 minutes capture was conducted in Ndop, we from mid-May to early-July (almost 2 months); larvae of multiply the mean abundance of this site by two, to stage 4 occurred from early-June to late-July (almost 1.5 compare it with those of Yaounde and Douala. The effect months); larvae of stage 5 appeared from mid-June to of sex, season and population type in Z. variegatus early-September (almost 3 months); larvae of stage 6 were abundance were analysed with the Kruskall-Wallis observed from early-July to late-September (almost 3 analyse of variance and Wilcoxon two samples tests months) and adults of the same population were observed using the NPAR1WAY WILCOXON procedure of SAS from mid-July right up to mid-December (almost 5 version 9.1. All significances were based on 5% months). The second annual population appeared by probability. late-October and disappeared by mid-May (about 7 months). The stage 1 larvae of this population appeared RESULTS from late-October to mid-November (almost 1 month); stage 2 larvae were present from late-October to mid- Presence of Zonocerus variegatus in the Natural Area: December (almost 2 months); stage 3 larvae appeared from In each site, Zonocerus variegatus was present late-October to late-December (almost 2 months); the throughout the year and two separate periods of presence stage 4 larvae occurred from mid-November to mid- for each post-embryonic stage were observed in the year January (almost 2 months); larvae of stage 5 appeared (Figs. 2-5). from late-December to early-March (almost 2.5 months); In Yaoundé, the first annual populations were stage 6 larvae were observed from early-January to early- observed from late-January to early–December (almost April (almost 3 months) and adults of this population 10.5 months). In this population, stage 1 larvae were appeared from mid-January to early-May (almost 4 observed between late-January and late-April (almost months) (Fig. 3).

90 Acad. J. Entomol., 7 (3): 88-101, 2014

Fig. 1: Cameroon relief and vegetation map (Bruneau, 1999)

91 Acad. J. Entomol., 7 (3): 88-101, 2014

Fig. 2: Temporal fluctuations in Zonocerusvariegatus abundance (60 minutes captures) in the semi-deciduous zone of Yaoundé (Southern Cameroon), from January to December 2011: (a) adult; (b) stage six larvae; (c) stage five larvae; (d) stage four larvae; (e) stage three larvae; (f) stage two larvae; (g) stage one larvae.

92 Acad. J. Entomol., 7 (3): 88-101, 2014

Fig. 3: Temporal fluctuations in Zonocerusvariegatus abundance (30 minutes capture) in the grassfields zone of Ndop (North-West, Cameroon), from January 2012 to January 2013: (a) adult; (b) stage six larvae; (c) stage five larvae; (d) stage four larvae; (e) stage three larvae; (f) stage two larvae; (g) stage one larvae.

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Fig. 4: Temporal fluctuations in Zonocerusvariegatus abundance (60 minutes captures) in the evergreen forest zone of Douala (Coastline zone, Cameroon), from April 2013 to April 2014: (a) adult; (b) stage six larvae; (c) stage five larvae; (d) stage four larvae; (e) stage three larvae; (f) stage two larvae; (g) stage one larvae.

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Fig. 5: Temporal fluctuations in Zonocerusvariegatus abundance (30 minutes captures) in the evergreen forest zone of Douala (Coastline zone, Cameroon), from April 2013 to April 2014: (a) adult; (b) stage six larvae; (c) stage five larvae; (d) stage four larvae; (e) stage three larvae; (f) stage two larvae; (g) stage one larvae.

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In Douala (Logbessou), the first annual population November with stages 1-5 larvae of the first population appeared by early-October and disappeared by late- (Douala) (Figs. 4-5). March (almost 5 months). In this population, the larval stage 1 were observed between early-October and Abundance of Z. variegatus in the Natural Area mid-November (almost 1.5 months); larvae of stage 2 Variation in Abundance Between the Three Sites: An appeared by early-October and disappeared by early- average of 39.46±2.93, 44.93±8.29 and 31.98±4.37 December (almost 2 months); larvae of stage 3 were individuals of Z. variegatus were collected in 60 min in the present from late-October to early-December (almost 1.5 semi-deciduous forest of Yaoundé, the grassfield zone of months); stage 4 larvae were present from late-October Ndop (North West Region) and the evergreen forest of to early-December (almost1.5 months); larvae of stage the coastline Region (Logbessou) respectively. The 5 were present from late-October to early-January number of individuals of Z. variegatus was very high in (almost 2.5 months); larvae of stage 6 were observed the grassfield zone of the North West region than in between early-December and mid-February (almost 2.5 Yaoundé and Douala. months) and adults appeared by early-January and disappeared by late-March (almost 2.5 months). The Variation in Abundance Between the First and Second second annual population appeared by late-December Population: In each site, one of the two populations and disappeared by early-November (almost 10.5 months). observed was more abundant (large population) than the In this population, the larvae of stage 1 were observed other (small population). between late-December and mid-April (almost 4 months); In Yaoundé, the first population (large population) larval stage 2 appeared by early-January and disappeared was more abundant (12.28±2.12) than the second (small by late-May (almost 4 months); larvae of stage 3 population) (8.15±5.01) (Table 1). By considering appeared by late-January and disappeared by mid-May individual developmental stages, there is no significant (almost 4 months); larvae of stage 4 appeared by early- difference between the abundance of the first and second March and disappeared by mid-May (almost 2 months); populations (Table 1). larvae of stage 5 appeared by mid-April and In the Grassfield zone of Ndop and evergreen forest disappeared by late-June (almost 3 months); larvae of zone of Douala, the first population was smaller than the stage 6 were observed from mid-April to early-August second (large). By considering individual developmental (almost 4 months) and adults were observed from early- stages, there is no significant difference between both May to early-November (almost 6 months). However, in populations for stages 5, 6 larvae and adult in Ndop Douala, while the two populations were clearly visible (Table 2) and between the first and second population of in the 60 minutes captures, the small population was less stage 1 larvae in Douala (Table 3). visible in the 30 minutes captures than that of 60 minutes (Fig. 4). Variation in Abundance Between Seasons: In Yaoundé (Center Region), the first annual population was present Overlap of the Two Populations in the Natural Area: during all the four seasons with non-significant difference In each site, the two populations live in the same place (Table 4). However, by considering post-embryonic and the adults, as well as the larvae of the two annual developmental stages, the young larvae (stage 1-3 larvae) populations of Z. variegatus did not overlap; but, the were only present during the long dry and short rainy adult of each population co-exist with the larvae of the seasons and the stage 1 larvae was significantly more next population. In fact, the adults of the first population abundant during the long dry season (36.29±20.90); stage co-exist: (a) from mid-September to mid-December with 4 larvae was only present in the short rainy and dry stages 1-5 larvae of the second population in Yaounde seasons with more abundance in the short rainy season (Fig. 2); (b) from late-October to early December with (15.60±12.81). The stages 5-6 larvae were absent during larvae 1-4 stages of the second population in Ndop the long dry season with high abundance of stage 6 (Fig. 3) and (c) from early January to late-March with larvae in the short dry season. Adult was present in the larvae 1-4 stages of the second population in Douala four seasons with long abundance in the long rainy (figures 4-5). Those of the second population co-exist: (a) season. The second annual population was present only in the month of March with the larvae 1-3 stages of the during the long rainy and long dry seasons with no first population of Yaounde (Fig. 2); (b) from late-April to significant difference of abundance between both mid-May with the larvae 1-3 stages of the first population seasons; however, the old larvae (stage 4-6) and adults of Ndop (Fig. 3) and (c) from early October to early were absent in the rainy season (Table 5).

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Table 1: The abundance of post-embryonic developmental stages of the small (second) and great (first) populations of Zonocerus variegatus in the semi- deciduous zone (Yaoundé), from January to December 2011 Populations Stage 1 larva Stage 2 larva Stage 3 larva Stage 4 larva Stage 5 larva Stage 6 larva Adult Average Great (First) 27.50±16.14 (10) 12.65±5.72 (17) 14.42±6.33(19) 11.23±5.48(22) 10.00±3.21(20) 10.50±4.18(18) 8.50±3.47 (26) 12,28±2.12(132) Small (Second) 15.00±11.82(8) 8.42±8.38 (12) 9.77±9.61 (9) 6.23±7.17 (8) 4.38±1.99(8) 6.00±7.24 (4) 1.00±2.48 (3) 8,15±5.01 (52) Z-value -1.0679 -1.5982 -1.1835 -0.7542 -1.7398 -0.9393 -1.6227 -2.6157 p-value 0.29 0.11 0.24 0.25 0.08 0.35 0.10 0.009 Each value in the table represents the mean (60 minutes capture per week) and standard deviation. p-value is the significant level of the Z-value (Wilcoxon two samples test). In bracket: number of samples.

Table 2: The abundance of post-embryonic developmental stages of the Small (first) and great (second) populations of Zonocerus variegatus in the grassfield zone (Ndop), from January 2012 to January 2013. Populations Stage 1 larva Stage 2 larva Stage 3 larva Stage 4 larva Stage 5 larva Stage 6 larva Adult Average Small (First) 2±2.07(8) 1.28±1.11 (7) 1.11±1.05(9) 1.57±1.13(7) 2.15±1.21 (13) 4.38±2.18(16) 3.41±3.42(22) 2.61±2.47(79) Great (Second) 22.21±12.36(5) 16.11±11.36(9) 24.27±14.49(11) 32.50±15.66(10) 6.53±9.19 (13) 2.71±1.98(14) 1.94±1.66(18) 12.58±14.66(80) Z-value 2.88 -2.45 -3.74 -3.29 0.53 1.89 -1.47 -4.25 P-value 0.004 0.01 0.0002 0.001 0.60 0.05 0.14 0.0001 Each value in the table represents the mean (30 minutes capture per week) and standard deviation. p-value is the significant level of the Z-value (Wilcoxon two samples test). In bracket: number of samples.

Table 3: The abundance of post-embryonic developmental stages of the Small (first) and great (second) populations of Zonocerus variegatus in the evergreen forest vegetation (Coastline zone: Douala), from April 2013 to April 2014 Populations Stage 1 larva Stage 2 larva Stage 3 larva Stage 4 larva Stage 5 larva Stage 6 larva Adult Average Small (Fisrt) 2±1.79 (6) 1.22±1.30 (9) 2±1.60 (8) 1.75±1.04(8) 1.36±1.63 (11) 0.70±1.06(10) 0.25±0.45(12) 1.22±1.37(64) Great (Second) 19.18±21.63(17) 15.05±17.97(19) 24.50±23.04(16) 7.27±3.04(11) 8.91±8.36 (11) 9.75±5.48(16) 7.89±5.66(27) 13.26±15.42(117) Z-value -1.72 -2.62 -3.19 -3.32 2.72 -4.04 -4.21 -8.54 p-value 0.08 0.008 0.001 0.0009 0.006 0.0001 0.0001 0.0001 Each value in the table represents the mean (60 minutes capture per week) and standard deviation. p-value is the significant level of the Z-value (Wilcoxon two samples test). In bracket: number of samples.

Table 4: The abundance of post-embryonic developmental stages of the great (first) populations of Zonocerus variegatus in the rainy and dry seasons of the semi-deciduous zone (Yaoundé), from January to December 2011 Seasons Stage 1 larva Stage 2 larva Stage 3 larva Stage 4 larva Stage 5 larva Stage 6 larva Adult Average Long rainy - - - - 1±0 (1) 9.33±5.51(3) 16.09±7.52(11) 13.73±8.05 (15) Long dry 36.29±20.90 (7) 18.17±13.66 (6) 5.2±6.14 (5) - - - 1.75±0.96 (4) 18±19.43 (22) Short rainy 7±8.89 (3) 9.64±8.74(11) 17.71±13.52(14) 15.60±12.81(15) 10.80±7.27(10) 2.50±2.35(6) 0.50±0.71 (2) 12.02±11.33(61) Short dry - - - 1.86±1.35 (7) 10.11±6.41 (9) 16.22±7.33(9) 4±4.24 (9) 8.41±7.72(34) H-value 4.69 1.85 3.79 8.43 1.78 11.13 16.04 5.35 P-value 0.03 0.17 0.05 0.004 0.41 0.004 0.001 0.147 Each value in the table represents the mean (60 minutes capture per week) and standard deviation. P-value is the significant level of the H-value (Kruskal Wallis test). In bracket: number of samples.

Table 5: The abundance of post-embryonic developmental stages of the small (second) populations of Zonocerus variegatus in the rainy and dry seasons of the semi-deciduous zones (Yaoundé), from January to December 2011 Seasons Stage 1 larva Stage 2 larva Stage 3 larva Stage 4 larva Stage 5 larva Stage 6 larva Adult Average Long rainy 15±14.14 (8) 3.38±4.34 (8) 1.67±2.08 (3) - - - - 8±11.12 (19) Long dry - 18.50±19.77 (4) 13.83±13.76 (6) 6.63±8.58(8) 4.38±2.39(8) 6±4.55(4) 1±1.41(2) 8.47±10.79(32) Short rainy ------1±0(1) 1±0(1) Short dry ------H-value - 3.24 3.32 - - - - -1.23 P-value - 0.07 0.06 - - - - 0.22 Each value in the table represents the mean (60 minutes capture per week) and standard deviation. p-value is the significant level of the H-value (Kruskal Wallis test). In bracket: number of samples.

97 Acad. J. Entomol., 7 (3): 88-101, 2014

Table 6: The abundance of post-embryonic developmental stages of the small (first) populations of Zonocerus variegatus in the rainy and dry seasons of the grassfields zone (Ndop),from January 2012 to January 2013 Seasons Stage 1 larva Stage 2 larva Stage 3 larva Stage 4 larva Stage 5 larva Stage 6 larva Adult Average Rainy 2±2.07 (8) 1.28±1.11 (7) 1.11±1.05 (9) 1.57±1.13 (7) 2.15±1.21 (13) 4.39±2.18(13) 4±3.5 (18) 2.71±2.49(75) Dry ------0.75±0.96 (4) 0.75±0.96 (4) Z-value ------2.23 -1.96 P-value ------0.02 0.0496 Each value in the table represents the mean (30 minutes capture per week) and standard deviation. p-value is the significant level of the Z-value (Wilcoxon two samples test). In bracket: number of samples.

Table 7: The abundance of post-embryonic developmental stages of the great (second) populations of Zonocerus variegatus in the rainy and dry seasons of the grassfields zone (Ndop), from January 2012 to January 2013 Seasons Stage 1 larva Stage 2 larva Stage 3 larva Stage 4 larva Stage 5 larva Stage 6 larva Adult Average Rainy 25±12.30 (4) 21.5±3.42(4) 13±9.66(4) - - 3.25±2.06(4) 2.56±1.88(9) 10.96±11.05(25) Dry 11±0(1) 11.80±14.04(5) 30.71±13.06(7) 32.5±15.66(10) 6.54±9.19(13) 2.5±2.01(10) 1.33±1.22(9) 13.31±16.08(55) Z-value -1.06 0.98 -1.80 - - 0.44 1.39 0.42 P-value 0.28 0.32 0.07 - - 0.66 0.16 0.67 Each value in the table represents the mean (30 minutes capture per week) and standard deviation. p-value is the significant level of the Z-value (Wilcoxon two samples test). In bracket: number of samples.

Table 8: The abundance of post-embryonic developmental stages of the small (fisrt) populations of Zonocerus variegatus in the rainy and dry seasons of the evergreen forest vegetation (Douala), from April 2013 to April 2014 Seasons Stage 1 larva Stage 2 larva Stage 3 larva Stage 4 larva Stage 5 larva Stage 6 larva Adult Average Rainy 1.25±1.26(4) 0.75±0.96(4) 3.5±2.12(2) 2.50±0.71(2) 2±0(1) - 0.25±0.50(4) 1. 35.±1.41(17) Dry 3.50±2.12(2) 1.60±1.52(5) 1.50±1.22(6) 1.50±1.05(6) 1.30±1.70(10) 0.70±1.06(10) 0.25±0.46(8) 1.17.±1. 37(47) Z_value 1.17 -0.76 1.07 1.04 0.50 - 0.00 0.56 p-value 0.24 0.46 0.28 0.30 0.62 - 1.00 0.57 Each value in the table represents the mean (60 minutes capture per week) and standard deviation. p-value is the significant level of the Z-value (Wilcoxon two samples test). In bracket: number of samples.

Table 9: The abundance of post-embryonic developmental stages of the great (second) populations of Zonocerus variegatus in the rainy and dry seasons of the evergreen forest zone (Douala), from April 2013 to April 2014 Seasons Stage 1 larva Stage 2 larva Stage 3 larva Stage 4 larva Stage 5 larva Stage 6 larva Adult Average Rainy 1.86±1.77(7) 5.58±8.65(12) 27.91±27.23(11) 7.27±3.04(11) 8.91±8.36(11) 9.75±5.48(16) 8.15±5.60(26) 9.93±12.57(94) Dry 31.30±20.82(10) 31.29±18.58(7) 17±6.04(5) - - - 1±0(1) 26.87±1.37(23) Z-Value -2.93 2.99 -0.23 - - - -1.16 4.16 p-Value 0.009 0.002 0.82 - - - 0.24 0.0001 Each value in the table represents the mean (60 minutes capture per week) and standard deviation. p-value is the significant level of the Z-value (Wilcoxon two samples test). In bracket: number of samples.

In Ndop (North West region), the first annual DISCUSSION population (small population) was significantly present during the rainy season. In the dry season, this The present study showed that, whatever the population was only represented by adults (Table 6). considered study site (semi-deciduous zone (Yaoundé) The second annual population (large) was present during with bimodal distribution of rainfall, grassfield zone the dry and rainy seasons with non-significant difference (Ndop) and ever-green forest vegetation (Douala) with (Table 7). unimodal rainfall), Zonocerus variegatus occurred In Douala (Coastline region), the first and second throughout the year, with two univoltine populations of annual populations were present during the two seasons unequal abundance and duration. The same type of life with non-significant difference for the first annual cycle has been reported in Yaoundé, Mbalmayo (semi- population (Table 8) and with significant difference for the deciduous zones) [8] and other forest regions with second (Table 9). The second population was more bimodal rainfall such as Ibadan (Nigeria) [12-16], Nsukka abundant in the dry season. By considering the post- (Nigeria) [17,18], lower Ivory-Coast [19] and Allada embryonic developmental stages, the old larvae was only (Benin) [20,21] and in other forest regions with unimodal present in the rainy season. rainfall such as Atigba (Togo) [22]. Different results have

98 Acad. J. Entomol., 7 (3): 88-101, 2014 been noticed in the preforest zones of Togo (Lomé), in the For Chapman et al. [4] and Toye-Afolabi [27] great forest zones of Sassandra (Ivory-Coast) [23], in Several abundance of is observed in the dry season and localities of South-East Ghana [23], in Kumasi [24], in the their scarcity during the rains. Although the expressions evergreen forest zone of Mayombe (Congo) [9]. In fact, in “dry season population” and “rainy season population” those areas, where the unimodal rainfall conditions are have been classically used to indicate the seasonal observed, Z. variegatus is also present throughout the alternance of populations [17, 29], such distinction is year but with a univoltine population [25]. The bivoltine difficult [8] when individuals of larval stages are taken population has been notice in some parts of the forest into consideration. Our results are so varied that it is belt of Ivory-Coast [23, 26]). These contrary opinions really difficult [8] to make such distinction in forest and may result from insufficiently precise observations grassfields areas of Cameroon. (absence of a thorough study of population dynamics) [26]. The Le Gall et al. [21] results would therefore be CONCLUSION related to inaccurate study because of the very low numbers of grasshoppers found. The small population is In Yaoundé, Ndop and Douala, Z. variegatus often very scarce, so it is hardly noticeable when the occurred in two annual univoltine populations of unequal duration of the capture is low. In fact, this small abundance and durations. The number of annual rainy population was less visible in Douala in the 30 minutes season is therefore not a factor of variation of the number capture (Fig. 5) where they appear more visible in the 60 of annual populations or generation of Z. variegatus. minutes capture (Fig. 4). The two populations live in the same place and the The Nanta results would also be related as suggested adults of one population co-existed with young larvae of by Anya [17] and De Gregorio [22] to insufficient the other population. Moreover, the adults, as well as the observations because the presence of a bivoltine larvae of the two annual populations did not overlap. population throughout the year would be impossible Seasonal changes have various effects on the abundance especially when we know that in most places, there is of both populations. The type of life cycle of Z. coexistence of young larvae of the first population and variegatus is the same throughout the Equatorial climate adults of the second population (Vice-versa). The long zone of Cameroon. duration of post-embryonic development of Z. variegatus (3-7 months) strongly suggest that each adult population ACKNOWLEDGEMENTS cannot be the parental population of the first nymphal instars with which the adults coexist [8]. This work was funded by the Ministry of Higher Although the two adult populations never overlap in Education quarterly funds put at our disposal. We also the period of occurrence in the present study (southern, thank the plant protection team for their help in the data northwest and coastal zones of Cameroon) and in collection. Southern Nigeria [27], the two adult populations coexist in Atigba (Togo) from December to January and from mid- REFERENCES May to mid-July [22] and in the Nsukka plateau (South- East, Nigeria), from June to August and copulated [17,28]. 1. Chiffaud, J. and J. Mestre, 1990. Le criquet puant However, there was no report of any viable offspring Zonocerus variegatus (Linné, 1758). Essai de being produced [27]. In addition, laboratory attempts to synthèse Bibliographique, Centre de Coopération make reproductively mature and copulating adult from Internationale en Recherche Agronomique pour le either seasonal population with each other were not Développement (CIRAD), Acridologie Opérationnelle successful [17]. Ecoforce International (PRIFAS), France, pp: 140. Unequal abundance of two annual populations 2. Kekeunou, S., 2007. Influence de différents types de of Z. variegatus noted in the Southern parts of végétations des jachères sur les populations de Cameroon had already been highlighted by Zonocerus variegatus (Orthoptera: Pyrgomorphidae) Chapman et al. [4], Toye-Afolabi [27] in Nigeria, Le Gall dans la zone de forêt humide du sud Cameroun. [20] and Le Gall et al. [21] in Allada (Benin) and Thèse de Doctorat. Université de Yaoundé I, Messi et al. [8] in the Southern Cameroon. Cameroon.

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