The incidence and distribution of the sorghum head bug, Eurystylus oldi Poppius (Heteroptera: Miridae), and other panicle pests of sorghum in research stations and farmers' fields in West and Central Africa (WCA) were assessed from 1985 to 1994. Maximum head bug abundance was observed during the dough stage. Head bug abundance was greater on improved cultivars, while the local guineense sorghums with long glumes were less susceptible, both at the research stations and the farmers' fields. Grain damage was moderate to severe, although farmers were mostly unaware of this insect and its damage potential, because it remains hidden inside the panicle. Sorghum midge (Stenodiplosis sorghicola Coq.) damage was very high on farmer's fields in Burkina Faso, Niger, and Nigeria. The shootfly Atherigona soccata Rond., stemborer Busseola fusca Fuller, grasshoppers, spittle bug Locris rubens Erichson, Campylomma spp., Creontiades pallidus Ramb., Agonoscelis spp., head caterpillars Helicoverpa armigera Hub., Pyroderces simplex Wlsm. and Eublemma gayneri Roths., were other insect pests damaging sorghum in the areas surveyed. It is proposed that future efforts in sorghum improvement for WCA should focus on developing cultivars with resistance to sorghum head bugs.

Cotesia flavipes (Hymenoptera: Braconidae) is a braconid larval parasitoid that has been used in the biological control of tropical stemborers in gramineous plants. The current research status on the behavioural ecology of this parasitoid is reviewed. The stimuli involved in the location of the host-microhabitat and the behaviour on infested plants and inside stemborer tunnels are discussed. Several aspects of the host foraging behaviour on C. flavipes are discussed in relation to the ecology of the parasitoid, such as the role of learning in foraging and clutch size allocation decisions. Variation in behaviour can be an obstacle in the effective use of natural enemies in biological control. Behavioural variation may exist because individuals differ genetically in their propensity to find or accept different hosts. Individuals may also differ because they have experienced different environments (i.e. learning). The second part of this paper focuses on the intraspecific variability in G flavipes behaviour and discusses to what extent the reported plant and host specificity in C. flavipes has a genetic basis or is due to phenotypic plasticity through learning.

Mexican bean weevil, Zabrotes subfasciatus Boheman, is a significant pest of stored beans (Phaseolus vulgaris L.) that causes considerable loss in the quality and quantity of bean grain in Africa. In the past two to three decades, researchers have attempted to identify botanicals with better insecticidal potential against storage pests. However, there is a lack of information on the potency of botanical combinations, their toxicology, and optimal application rates. This study was conducted to examine the bioefficacy of unitary and binary botanical combinations of Jatropha curcas (L.), Datura stramonium (L.), Chenopodium ambrosioides (L.), Schinus molle (L.), and Azadirachta indica (A. Juss) against Z. subfasciatus at 1% and 2% w/w dosages. The insecticidal activities of the botanicals were measured based on their effect on adult mortality of Z. subfasciatus and progeny reduction, grain weight loss, and weevil perforation index. Among botanical admixtures, binary combinations of C. ambrosioides + D. stramonium, J. curcas + C. ambrosioides, and S. molle + C. ambrosioides were the most potent. They resulted in the highest mortality of Z. subfasciatus, low weevil perforation index or none, and grain weight loss at the most moderate test dosage (1% w/w). Treatment with C. ambrosioides resulted in the highest efficacy when applied individually. We failed to observe any notable difference in toxicity between dosage levels among the binary botanical combinations. However, the effectiveness of unitary formulations improved with the increase in dosage rate. Application of botanicals did not adversely affect bean seed germination. Our study suggests that botanicals in binary mixtures may enhance the potency of constituent components for effective control of Z. subfasciatus.

Aqueous extracts (5%) of the seeds Parkia clappertoniana (Jacq), Azadirachta indica A. Juss, and Piper guineense Schum and Thonn caused 90% mortalityof the worker caste with P. guineense, and 86% mortality with A. indica and P. clappertoniana respectively within 3 hr of topical application. At 24 hr, mortality of Macrotermes nigeriensis (Sjostedti) workers was 100% with the same concentration of each extract. Oral toxicity at 3 hr to the worker caste using cuttings of cassava, Manihotesculenta Crantz impregnated with each extract gave 65% mortality with Piper, and 45 and 29% with Azadirachta and Parkia, respectively. Mortalityby oral toxicity reached 100% in 12 hr with Piper, 95 and 69%, respectively with Azadirachta and Parkia. Increasing the concentrations of each extract to 15% did not significantly (P > 0.05) increase the toxicities of the extracts to the worker caste even at prolonged exposure periods.

In the present study, four methods of rice crop establishment, viz. conventional transplantation, bed transplantation (BT), furrow transplantation (FT) and puddled direct seeding (PDS), were evaluated during two wet seasons to determine their influence on the incidence of insect pests and grain yield. Observations were recorded starting from 40 days after transplanting (DAT) and seeding (DAS) to 110 DAT and DAS. The interaction between crop establishment methods and observation days was significant in the case of folded leaves by Cnaphalocrocis medinalis (Guenée), deadhearts by Scirpophaga incertulas (Walker) and the Sogatella furcifera (Horvath) population. The number of folded leaves in the bed-transplanted crop (8.87%) and puddle direct seeded crop (10.62%) was significantly higher than that in crop grown using the other crop establishment methods. The incidence of deadheart damage was significantly higher in the PDS plots (5.85%), while that of whitehead damage was higher in the BT (5.89%) and PDS (6.54%) plots than in the plots managed by the other methods. The S. furcifera population build-up was significantly higher in the FT (1.98 hoppers/hill) and PDS (2.24 hoppers/hill) plots than in the plots managed by the other crop establishment methods. Paddy yield was significantly higher in the conventionally transplanted crops followed by the furrow- and bed-transplanted crops.

Laboratory experiments were conducted to investigate the effect of diet on the biology and prédation capacity of the phytoseiid mite Amblyseius zaheri Yousef & El-Brolossy. The predatory mite was able to develop and reproduce when fed on nymphs of the twospotted spider mite Tetranychus urticae Koch, nymphs of the citrus brown mite Eutetranychus orientalis Klein, motile stages of the eriophyid mite Eriophyes dioscoridis Soliman & Abou-Awad, eggs of the scale insect Parlatorio ziziphus Lucas, nymphs of the whitefly Bemisia tabaci (Genn.) and pollen grains of date palm, Phoenix dactylifera. The predatory mite's development was fastest on a diet of nymphs of Er. dioscoridis. All of the diets led to a female-biased progeny, which was most pronounced in predators fed on date palm pollen. The results are discussed in light of the biological control capacity of the phytoseiid mite.

In a bluetongue (BT) disease project, light trappings of Culicoides were conducted in 19 localities and 39,000 biting midges were examined. BT virus type 16 was isolated in 1968 at Devora from a pool consisting mainly of Culicoides schultzei gp and C. imicola; BT virus type 4 was isolated in 1969 at Yesodot from a pool of 183 C. imicola; BT virus type 2 was isolated in 1979 at Talmé El'azar from pools consisting of 2462 C. imicola; and BT virus type 6 was isolated 3 times in 1980 at Bet Dagan from pools of 204, 258 and from 143 C. imicola, respectively. In the Akabane project (1976 and 1977) 4632 Culicoides and 1867 mosquitoes from four localities were trapped and examined. An arbovirus which was not Akabane, BT or turkey meningo-encephalitis (TME) was isolated from a pool of 44 engorged Culex pipiens complex trapped in Gan Shemuel. In the Rift Valley fever project, which was conducted in 1978 and 1979 due to the presence of an epidemic in Egypt, 351 mosquitoes of four species and 7098 Culicoides of 14 species were tested and none were found to harbour an arbovirus. Within the TME project more than 12,000 Culicoides and 9000 mosquitoes from 14 localities were tested. Positive isolations of TME were made from an unsorted pool of mosquitoes from Gesher haziw, an unsorted pool of 13 Culicoides from Nahalal, a pool of 223 unidentified Culicoides from Zetan and a pool of 12 engorged Cx pipiens complex from the same locality. Other pathogens which were not identified to species level were also isolated.

In West Africa, Callosobruchus maculatus Fabricius mainly develops on cowpea (Vigna unguiculata (L.) Walpers) and sometimes on Bambara groundnut (Vigna subterranea (L.) Verdcourt). A survey on the development of a C. maculatus strain selected on cowpea was undertaken during eight generations on two local varieties of Bambara to determine their level of acceptability and suitability for the pest and its evolution over time and successive generations. When C. maculatus females were in contact with seeds from both Bambara varieties for the first time, they laid fewer eggs on these hosts in comparison with cowpea. However, females that have developed inside Bambara cv. Local Beige seeds deposited more eggs on their hosts of origin from the first generation onwards. The same result was obtained on Bambara cv. Local Striped seeds from the F4 generation onwards. Egg viability was not affected by host variability. On the contrary, the larval survival was significantly reduced on Bambara seeds. Larval survival and intrinsic rates of natural increase were improved on both Bambara varieties with successive generations in comparison to cowpea. Our results demonstrate that in a non-choice situation, C. maculatus is able to develop on both Bambara cv. and even increase its reproduction potential over successive generations, regardless of the climatic variations. The results help to better understand why C. maculatus is becoming a serious concern on Bambara in West Africa where the pest is frequently in contact with this occasional host.

Food consumption and utilization of a bivoltine silkworm hybrid was studied to understand the efficiency of food conversion into larval body, cocoon and cocoon shell during the life cycle. The ingesta, digesta, excreta, reference ratio, mean daily food ingested and digested in different larval instars were recorded. All these parameters differed from one larval instar to another. The AD and ECI were inversely correlated with the larval age. The ECI and ECD for body, cocoon and cocoon shell were 23.63, 17.59, 9.496 and 55.12, 46.65 and 25.23% respectively. Ingesta and digesta required to produce a gram body weight, progressively increased from first to fifth instar. Ingesta and digesta for one gram body, cocoon and cocoon shell production were 4.402, 5.762, 10.649 g and 1.840, 2.184 and 4.047 g respectively.

In order to predict host accessibility by the pupal parasitoid Xanthopimpla stemmator (Thunberg), four grass species (Sorghum bicolor, Pennisetum purpureum, Sorghum arundinaceum and Zea mays) were sampled for stemborer pupae in Kwale, in the low altitudes of southern Kenya, and in Trans-Nzoia, in the high altitudes of western Kenya. The pupal position of Chilo orichalcociliellus (Strand), Chilo partellus (Swinhoe), Sesamia calamistis Hampson, Sesamia sp. nr oriaula (Tams and Bowden) and Busseola fusca (Fuller) in the plant were determined in relation to (a) the distance of pupae from the edge of the stem (depth), (b) the distance between the moth-exit hole and the head of the pupa (location) and (c) the length of the tunnel from the moth-exit hole to the base of the tunnel. Pupal depth and location for C. partellus and B. fusca varied significantly in the different plant species tested, and the pupae tended to be embedded deeper in cultivated than wild hosts. On all host species, the borers were located at a depth less than 0.35 cm. Most C. orichalcociliellus and S. calamistis pupae were found pupating in the ears of maize or the upper part of the wild hosts' stem. Sesamia sp. nr oriaula was only collected from the lower parts of P. purpureum. For B. fusca, tunnel length varied significantly among plant species and was longer in cultivated hosts. Xanthopimpla stemmator has an ovipositor length of about 0.52 cm, thus it is anticipated that the parasitoid could easily reach and parasitize the pupae in these host species.

Studies on breeding sites of Phlebotomus duboscqi, a vector of Leishmania major, were intensified in Marigat, Baringo District, Kenya using the soil incubation technique, following the previously successful attempt to look for sandfly breeding sites. Soil samples obtained from nest areas of the animal burrows yielded Phlebotomus duboscqi and Sergentomyia ingrami. These two species had been shown to harbour L. major parasites inside animal burrows. Other phlebotomine sandflies recovered from these same breeding sites included P. martini, P. rhodhaini, S. bedfordi, S. africanus, S. antennatus and S. graingeri

Differences in population growth among four variation types of the ladybird beetle, Harmonia axyridis Pallas, namely succinea, conspicua, spectabilis and aulica, were investigated using various growth parameters. The variation types showed three growth patterns from the intrinsic growth rates (rm), with rates of 0.093–0.099 (for conspicua and aulica), 0.073 (for succinea) and 0.040 (for spectabilis). The growth rates of these patterns were realised in different ways. Spectabilis differed from the other three types in the age and per cent distribution of the specific period to the rm values.

Shade-dried, powdered drupes of Melia azedarach L. were selected from three states in India, each representing a different geographical region, viz. Rajasthan (arid), Punjab (open plains), and Himachal Pradesh (hilly). Drupes were extracted in chloroform: methanol (9:1) and evaluated against second instar larvae of Plutella xylostella (Linnaeus) using a ‘leaf-disc dip’ bioassay. The ecotype from the arid region of Rajasthan yielded the lowest LC50 (1.47%), followed by that from the open plains of Punjab (1.79%) and the hilly areas of Himachal Pradesh, which yielded the maximum LC50 (2.29%). The survivors demonstrated various types of sublethal effects such as prolongation of larval period (7.0–7.8 days compared to 6.3–6.5 days in the control), reduction in pupal weight (36.0–38.4 mg/10 pupae in comparison to 54.4–56.0 mg in the control), deformation of pupae (up to 69.7%) and inhibition of adult emergence (up to 92%). A highly pronounced curtailment of fecundity (up to 10.4 against 73.2 in the control), significant reduction in oviposition period of the adults (up to 3.5 days compared to 7.4 days in the control) and longevity (5.5–7.8 days against 8.9–10.3 days in the control), were also recorded. The extracts produced from trees in the arid region of Rajasthan caused both lethal and sublethal effects following treatment of the second instar larvae of P. xylostella. Only 1.0% normal adults survived at the end of the study compared to 3.5 and 5.5% adult survival in the extracts from the open plains and hilly area ecotypes, respectively. An understanding of the bases of these variations in the toxicity of the crude extracts from the M. azedarach ecotypes growing in different climate conditions may open up the possibility of propagation and genetic improvement of the desired traits in the future.

In the field and laboratory, Gossypium arboreum varieties G 27, LD 133 and LD 230 were less preferred by the jassid, Amrasca biguttula biguttula, and the aphid, Aphis gossypii, than G. hirsutum variety, F 414. The arboreum varieties also supported fewer numbers of the two sucking pests than the hirsutum cotton. These varieties proved potentially susceptible to bollworms Earias spp and Pectinophora gossypiella damage in laboratory tests. Interestingly the varieties exhibited considerable degrees of field resistance. In the field, Earias moths showed no preference for any plant part for oviposition among the four cotton varieties. Of the reproductive parts of the cotton plant offered, first and last instar Earias vittella larvae orientated maximally to bud. Nonetheless, the larvae showed no definite pattern of preference for the fruiting structures of the cotton plant. In the laboratory, the four varieties showed non-significant differences in supporting the growth of Earias and Pectinophora larvae. The number of Earias eggs on the four varieties did not vary significantly. The number of fruiting bodies per plant and Earias incidence were unrelated in the four varieties.

Differences in the susceptibility or resistance of different plants to an insect are reflected in the magnitude of its population established on them and the resulting damage. The population of an insect on a plant is determined by an interaction between its responses and the plant's characters. As explained previously, the following six main types of responses, operating in as many stages, are involved in the establishment of an insect on a plant: (1) orientation, determining the insect's arrival on or avoidance of a plant in response to its attractant or repellent stimuli; (2) feeding responses, determining the quantity of food ingested from the plant; (3) metabolic responses involving the utilisation of the ingested food and determining the insect's nutrition; (4) development of the insect, if in the larval stage, determined by the quantitative food-intake and nutrition; (5) egg-production in the adult stage, determined by the quantitative food-intake and nutrition; and (6) oviposition.

The first, second and last of the above mentioned responses are behavioural which determine the initial selection or rejection of a plant by an insect. In order, therefore, to understand the principles governing the susceptibility/resistance of plants to an insect species, it is necessary to compare the above mentioned responses to susceptible and resistant plants and, next, to examine the role of the plant characters in determining these responses.

On the basis of the existing literature on the subject, the role of different behavioural responses of insects to plants and their characters in determining their susceptibility or resistance to their insect pests has been considered in this paper.

The effect of fluoride on the food and dietary water intake and utilisation were studied in final instars of silkworm, Bombyx mori L. race NB4D2 fed ad libitum with mulberry leaves treated with sodium fluoride at concentrations of 25 ppm, 50 ppm and 75 ppm. The larval duration increased by two days while food consumption, assimilation rate, assimilation efficiency, feeding and metabolic rates increased significantly in all the treated larvae. On the other hand, the amount of faeces produced, food conversion, conversion rate and conversion efficiencies decreased significantly in all the treated batches when compared to controls. The water intake and utilisation parameters increased significantly while rate of water loss through faeces, water retained in the body and retention efficiency decreased in all the fluoride-treated silkworms. The factors responsible for these changes in treated batches are discussed in relation to the effect of fluoride on cocoon and shell weights.

The development and pest status of Aspavia armigera on two cowpea varieties viz: Ife Brown and TVU1890 and alsoon two upland rice varieties viz: ITA 128 and ITA 257 were studied under ambient conditions in the laboratory and at the roof-top garden, Department of Agricultural Biology, University of Ibadan, Nigeria.

The oviposition periods on rice were 15.1 and 6.0 days respectively on ITA 257 and ITA 128; and on cowpea 10.6 and 8.5 days respectively on Ife Brown and TVU 1890. Fecundity was low. Mated females laid the highest number of eggs (24.6) on the cowpea Ife Brown and this was significantly higher than in the other cultivars. Mated and unmated males and females lived longer on Ife Brown and ITA 257 than on ITA 128 and TVU 1890.

The developmental period (nymph to adult), was shorter on ITA 257 (23.3 days) and Ife Brown (22.9 days) than on ITA 128 (23.3 days) and TVU 1890 (25.3 days). There were five nymphal instars and the mean growth ratio of head capsule measurements was 1.32.

Infestation at the level of two A. armigera per peduncle caused total seed losses in the two cowpea varieties whereas four and eight bugs per panicle caused 39.1 and 31.7 % grain yield losses in ITA 257 and ITA 128 rice varieties respectively.

The effects of established phenomena of plant resistance on the levels of tolerance to malathion of an organophosphate resistant strain of Myzus persicae were investigated using topical application insecticide bioassay. Tolerance was significantly decreased when aphids were reared on the moderately aphid-resistant Brussels sprout variety Early Half Tall or on sprout plants given reduced nitrogen fertilization. Differences in insecticide tolerance were found to occur only at older plant ages. It is argued that the differences (less than 50% in LC50 terms) reported are of practical importance, and attention is drawn to much greater differences (5-fold) obtained in experiments at different times of the year.

In the major breeding areas of tropical migratory locust, Locusta migratoria migratorioides (R. & F.) in Mali, Chad, Sudan and Madagascar, man has played a vital role in maintaining locust numbers above the levels found in undisturbed environments, through his agricultural and pastoral activities. Recent rapid agricultural development, particularly broad-acre cultivation of mono-cotyledonous summer crops in areas climatically suitable for migratory locust, has caused population upsurges in new areas, which have occasionally led to outbreaks and plagues. Some outbreaks appear to have been a reaction to the initial disturbance and have never recurred while others recur when meteorological conditions are favourable. Continued agricultural development in tropical and sub-tropical areas of the Old World will bring the risk of further upsurges of tropical migratory locust.

Recent developments in the assessment and collection of yield loss data due to pests are discussed. The information is needed for decision-making on resource allocation, on pest management, crop production planning and crop improvement. The difficulties in accurate loss assessment include lack of information on the distribution of pests in space and time, the difference between research and farmers yields, how much control has been used, and changes in crop resistance and in pest status. Sources of data are described and examples of losses in a number of tropical crops. The difficulties met in using losses to justify research and crop improvement projects, with particular reference to banana pests in Tanzania and cassava pests in Ghana, include the absence of reliable data, the selection of a base-line yield and the effects of other causes of loss.