Pitfall-trap sampling was used to determine the activity (numbers collected as determined by locomotor activity and density) of epigaeic (soil-surface dwelling) arthropods in rice cultivated at various toposequence sites on the slope of an inland valley in Bouaké, Côte d'Ivoire, West Africa in 1994–1996. The major arthropod groups collected were ants, spiders, crickets, carabids and grasshoppers. Ants and spiders were the most active. Arthropod activity changed in response to crop growth stage with activity generally increasing towards harvest. Ant activity differed significantly between toposequence sites and was highest in the upper portion of the slope. The pattern for spider activity in relation to toposequence site varied among years. Agronomic practices that would enhance the populations of ground-dwelling predaceous arthropods are an important consideration when developing cultural practices for rice production on hillsides of inland valleys in West Africa.

The biology of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), on four legumes (faba bean, field pea, lentil and grass pea) was studied in a greenhouse during the 1999/2000 seasons. There was no significant difference in length of nymphal period and number of moults (instars) among the crop species tested. The aphids generally took 9 to 11 days to reach the adult stage with a maximum of 3 moults. Lifespan was significantly longer on lentils than on other crops. Significantly more aphids survived beyond 15 days on lentil than on other crops. Similarly, the reproductive and post-reproductive period and adult longevity were longer on lentil. The pre-reproductive period was significantly higher on field pea than on the other crops. The net reproductive rate (R0) was highest on lentil (103.56 females /female) arid the intrinsic rate of increase (r) was highest on faba bean due to a short generation time (14.27 days). Generally, lifetime fecundity was higher on lentil (115.10/female) due to a higher daily reproduction rate (6.7 nymphs/female/day) on this crop. Nymphal production per aphid was strongly and positively correlated with lifespan, reproductive period and adult longevity but not of the nymphal period. Daily nymph production was significantly correlated with minimum temperature on lentil alone (F = 4.61, P < 0.05). Knowledge of the crop species and varieties susceptible to pea aphid is useful for identifying diets for the mass rearing of aphids for use in resistant variety selection and as diet for artificial natural enemy production. The present experiment indicates that lentil is suitable for both purposes.

In the present study, Y-tube olfactometric assays confirmed that volatiles from maize seedlings infested with Chilo partellus larvae were more attractive to the borer's larval endoparasitoid Cotesia flavipes, than volatiles from uninfested maize. Coupled gas chromatography-electroantennographic detector (GC-EAD) analysis of the volatiles from larvae-infested maize revealed six electrophysiologically active compounds on the antennae of the female parasitoid. These compounds were identified by GC-MS as (Z)-3-hexenyl acetate, linalool, (E)-4, 8-dimethyl-1, 3, 7-nonatriene, heptanal, (E)-β-ocimene and a C-5 aliphatic compound. (E)-4, 8-Dimethyl-1, 3, 7-nonatriene was present in EAG-detectable amounts in the volatiles of uninfested seedlings. In bioassays, a blend comprised of (Z)-3-hexenyl acetate, linalool, (E)-4, 8-dimethyl-1,3,7-nonatriene, (E)-β-ocimene and heptanal was significantly attractive to the parasitoid. Of the individual compounds, (Z)-3-hexenyl acetate was attractive at the doses tested while (E)-4,8-dimethyl-1,3,7-nonatriene and heptanal showed varying degree of attractiveness to the parasitoid at different doses. Linalool and (E)-β-ocimene were unattractive at the same doses. The significance of these results is discussed.

The incidence of the American serpentine leafminer, Liriomyza trifolii (Burgess) (Diptera: Agromyzidae) was studied in cotton-growing tracts of Tamil Nadu State, India. The incidence was higher on summer than on winter cotton and the cropping pattern was found to have an impact on the incidence of the leafminer on cotton. Biological studies on L. trifolii conducted on cotton, Gossypium hirsutum L., tomato, Lycopersicon esculentum Mill., and cowpea, Vigna sinensis (L.) Walp., revealed that its life cycle varied with different hosts. The duration of the pupal stage of L. trifolii was the longest in the leafminer's life cycle. Lycopersicon esculentum was the preferred host—females of L. trifolii survived the longest and had the highest fecundity on this host. Sex discrimination was possible at the pupal stage, on the basis of size; female adults were found to emerge from larger-sized pupae and males from smaller ones.

Studies on the population dynamics of Aphis gossypii Glover carried out on cotton in the Tadla area over a 3-year period showed two periods of rapid resurgence: June-July and September, with the highest density reached in the latter month accompanied by considerable indirect economic loss. The resurgence of Aphis gossypii populations on cotton depends mainly on the date and the density of contamination flights. The evolution and other factors responsible for the variations in the population dynamics are discussed.

Different blends of five chromatographically prominent components of the pheromone emission of gregarious-phase mature desert locust Schistocerca gregaria (Forskål) (Orthoptera: Acrididae) males were bioassayed for their maturation-accelerating effects on immature counterparts. The blend of all five components, namely anisóle, veratrole, benzaldehyde, phenylacetonitrile and 4-vinylveratrole was as effective as the emission from live mature males in accelerating the onset of mating in immature males. Subtraction of anisóle had no significant effect but removal of any one of the other four components significantly reduced the acceleration potency of the resulting blends. The maximum reduction occurred in the absence of phenylacetonitrile which appears to be critical to the activity of the blend. The magnitude of reduction in maturation acceleration that resulted from the subtraction of the other three components suggests that, although present in lesser relative amounts, these compounds contribute significantly to the activity of the full blend. Some differences were found between the onset of integumental yellowing and mating which indicate that blends of slightly different compositions are involved in promoting these two physiological processes.

Experiments were carried out to determine the factors that influence the feeding behaviour of Culex tigripes, a mosquito whose larvae are predators of other mosquito larvae. The results indicated that the efficiency of predatory activities of Cx tigripes larvae increased as they developed from 1st to 4th instar with regard to the number of mosquito prey larvae they consumed in a given period of time. Fourth instars of Cx tigripes are the most voracious of all the stages and are better adapted for catching and consuming all stages of mosquito larvae. The mean number of mosquito larvae consumed in 24 hours increased with increasing prey density. When offered a mixture of different prey species and larval stages, Cx tigripes larvae consistently selected 4th instars of mosquitoes over pupae and preferred Aedes aegypti larvae to the larvae of Cx quinquefasciatus and Anopheles gambiae. Prey size, density and mobility were also found to influence prey selection by Cx tigripes.

The biology, insect density-yield loss relationships, genotype reactions, and consumption and utilisation of food by the legume pod borer, Maruca vitrata (Fabricius) on pigeonpea (Cajanus cajan) and Adzuki bean (Phaseolus angularis) were studied. Post-embryonic development was completed in 20.2 to 22.6 days. Grain yield in plants infested with 2 and 4 larvae was the same as that in uninfested controls, while plants infested with 8 and 16 larvae suffered between 50–68% grain yield loss in pigeonpea and 61–71% in Adzuki bean. Food consumption by third instars was highest on ICPL 90011. This genotype had the lowest approximate digestibility (AD) and efficiency of conversion of ingested food (ECI). The significance of these results in relation to economic damage thresholds is discussed.

The leaf miner Coelaenomenodera lameensis Berti and Mariau (Coleoptera: Chrysomeiidae, Hispinae) is the main oil palm pest in Africa. A study of variations in its fecundity, in space and time, was carried out at 7 plantations and 19 sites in Côte d'lvoire. Fluctuations in fecundity, which could vary from almost 300 eggs to just a few eggs per 90-day period, were very similar at the various sites of the same plantation, and at the sites of different plantations, even when these were very far apart from each other. Fecundity increased with temperature, but other climatic factors were also important, with air saturation deficit playing a decisive role. The drier the air, the lower was the fecundity, which could even reach almost zero. As this parameter had a considerable impact on palm leaves' stomatal opening, a highly significant correlation was established between the latter and fecundity. Food supplies for larvae and adults can also affect fecundity, which seems to vary with the potassium content of the leaves.

The unsaponifiable matter and fatty acid methyl esters of the petroleum ether extract of seven plants with known acaricidal activity were fractionated and identified by GC chromatography, and their biological activity against the two-spotted spider mite, Tetranychus urticae Koch. (Acariforms: Tetranychidae) assayed. In general, unsaponifiable matter showed higher acaricidal activity than the saponifiable matter. The unsaponifiable matter of Dodonaea viscosa leaves was the most toxic and that of Callistemon lanceolatus leaves the least toxic. The saponifiable matter (fatty acids) of Curcuma longa was the most potent.

A study was undertaken to test the hypothesis that the quality of host plant parts determines the nutritional quality of herbivorous insects feeding on it to their parasitoids. A Gossypium hirsutum-Helicoverpa armigera-Campoletis chlorideae tritrophic system was evaluated. The superior nutritional quality of bolls and young leaves of Gossypium hirsutum (MCU-5 variety) contributes to more efficient feeding, growth and reproduction of the bollworm, Helicoverpa armigera (Hübner) and better survival of its larval parasitoid, Campoletis chlorideae Uchida. Longer total developmental duration and decrease in adult longevity were observed in H. armigera reared on senescent leaves than in those reared on bolls. Consumption, growth rate and efficiency measures were significantly lower in parasitised H. armigera larvae than in unparasitised larvae. Percentage parasitism was highest (84.1%) in H. armigera fed on bolls. The parasitoid C. chlorideae displayed shorter developmental duration and improved survival on H. armigera fed on bolls.

Laboratory parasitisation rates of a native (Indian) and an exotic (Indonesian) population of the gregarious larval endoparasitoid Cotesia flavipes Cameron (Hymenoptera: Braconidae), mass reared by the group-exposure method in glass chimneys, were examined during 1990–1994 on three hosts, namely the sugarcane shoot borer Chilo infuscatellus Snellen, sugarcane internode borer Chilo sacchariphagus indicus (Kapur) and spotted stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). Parasitisation rates of both the Indian and Indonesian populations in individual rearing batches showed considerable variation. Correlation and multiple regression analysis of parasitisation rates in rearing batches and three rearing parameters, viz. percent males, number of larvae and number of larvae per female parasitoid, indicated variable influence of the rearing parameters. Parasitisation rates of the Indian population were positively related to percent males and negatively related to number of larvae and number of larvae per female parasitoid in some hosts. The parasitisation rates of the Indonesian population were negatively related to percent males only in Ch. partellus. Mean monthly parasitisation rates of both populations during the study period fluctuated considerably in different hosts. The role of rearing parameters as well as rearing history of host and parasitoid cultures in parasitisation rates is discussed.

The life cycle and development of Zonocerus variegatus (variegated grasshopper) from southern Benin was studied at the International Institute of Tropical Agriculture (IITA) Benin Station, from March 1992 to August 1994. Hoppers of the 1st to the 5th stage were collected from uncultivated fields in the Atlantic Province and placed in cages and their development evaluated by counting the number of insects in each stage every two days until the adult stage. Mating and the number of egg pods were also recorded. The study showed that Z. variegatus has only one generation in southern Benin, running from September/October to July/August. Hatching occurs between September/ October and February/March. Zonocerus variegatus females can oviposit up to five times and the interval between ovipositions varies from 14 to 32 days. The variegated grasshopper has an egg diapause and egg hatching is not synchronised. These observations explain the almost perennial presence of the variegated grasshopper in southern Benin.

The development and morphometrics of the whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) were studied on cassava and a description was made of the different nymphal instars and oter biological characteristics. The nymphal instars were distinguished using easily recognisable morphological characteristics. Abnormally developing individuals were also easily recognised. Regression analysis was highly significant between the length and width of nymphal instars modelled collectively indicating two-dimensional growth at least across three nymphal stadia. Males were smaller than females on the basis of body length, wing width and width of the abdomen. The insects showed better development on a Colombian cassava variety as compared to an African variety, Ebwanateraka from Uganda, and consistently showed a higher proportion of males than females (2.33: 1) for early-emerging individuals. Mean developmental period on both varieties was 22 days and the first instars accounted for the major part of the developmental period which ranged from 19 to 29 days. The mean number of eggs/female/day was 4.89. The actual events of first instar eclosion, which can last up to approximately five minutes, were described. The intervals of honeydew flow to the vasiform orifice lasted a minimum mean time of 20.8 seconds and a maximum mean time of 123 seconds.

Preferences of Maruca vitrata (Fabricius) (Lepidoptera: Pyralidae) larvae to flowers, flower buds and pods of three different varieties of cowpea (IT 82E-666, IT 82D-716 and Botokpoyi) were studied in the laboratory using a four-branched olfactometer. For each plant part, fourth instars of M. vitrata were individually exposed to a set of three odours obtained from the cowpea varieties with pure air serving as the control. Movements of the larvae in the exposure chamber were followed at two levels of choice. Results from the first level of choice showed that the attractiveness of a particular plant part to M. vitrata larvae was not significantly influenced by variety. At the second level of choice a weakly significant preference was found for flowers (P = 0.1218) compared to pods (P = 0.7530) and flower buds (P = 0.6172). In all cases, no significant difference was found between the control (pure air) and the varieties.

Forty forage sorghum genotypes, including 30 hybrids, 5 inbred forage varieties and 3 resistant and 2 susceptible checks were screened for resistance to the sorghum shootfly, Atherigona soccata (Rondani) (Diptera: Muscidae) and the spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) under natural infestation in July-September 1996 and 1997. Six sorghum genotypes including two forage sorghum hybrids, HH 1 and NFSH 10659, three resistant check entries, IS 2205, IS 5469 and IS 18551 and inbred forage variety HC 171 showed multiple resistance to both the shootfly and the stemborer. The forage sorghum hybrid HH 1 also gave the highest green fodder yield. It is therefore suggested that this cultivar may be used in breeding programmes as a donor parent for developing sorghum cultivars resistant to A. soccata and C. partellus, or used directly for general cultivation.

Growth, development and fecundity of Maruca vitrata Fabricius (Lepidoptera: Crambidae) were studied on artificial diet and flowers of two accessions each of three wild Vigna species, namely V. vexillata (TVnu 594 and TVnu 72), V. oblongifolia (TVnu 957 and TVnu 42) and V. unguiculata ssp. dekindtiana (TVnu 979 and TVnu 863) and six accessions of cowpea, V. unguiculata ssp. unguiculata (Moussa Local, VICAM-1, TVu 13731, IT84S-2246, IT89KD-457 and IT91K-180). The percentage survival of the larvae, larval weights as well as growth and development indices were significantly higher on the artificial diet, flowers of cowpea cultivars and those of V. unguiculata ssp. dekindtiana compared to those of V. vexillata and V. oblongifolia. The fecundity of females from larvae reared on artificial diet and flowers of cowpea was also significantly higher than that of females from the wild Vigna genotypes. All variables were included in principal component analysis. Two components accounted for 81.79%. On the basis of this analysis, the diets appeared to fall into four categories based on their suitability for supporting development of M. vitrata: unsuitable (TVnu 42 and TVnu 957), fairly suitable (TVnu 72, TVnu 594, TVnu 979, Moussa Local and TVnu 863), suitable (IT89KD-457, IT91K-180, VICAM-1, TVu 13731 and IT84S-2246), and very suitable (artificial diet). The importance of these findings in the development of host plant resistance of cowpea to M. vitrata is discussed.

The oviposition-deterrent and toxic effects of seven plant species with known biological effects were tested against the Adzuki bean beetle, Callosobruchus chinensis L. (Goleoptera: Bruchidae) on stored faba bean seeds for two years at Holetta Research Centre, Ethiopia. Oils of Azadirachta indica, Milletiaie ferrnginea and Chrysanthemum cineraraefolium were the most effective in partially or completely preventing egg laying, and no bruchids emerged from the few eggs laid. The Phytolacca dodecandra, Hagenia abyssinica and Schinus molle treatments had no significant effect on the bruchids and most of the eggs laid developed into adults. Eucalyptus globulus seed powder treatment caused the death of only emerging adult beetles.