Agromyzidae populations occurring in legumes in Kenya were tested for speciation at host-type level and at the species level using discriminant analysis. Measurements were taken of various morphological characters of five populations of Chromatomyia horticola from five host plants and of seven male and female agromyzid species. The ratio of the proximal to the distal part of the wing vein, (M3+4) provided the best discrimination for five host populations of C. horticola; the species was separated into two distinct groups by this character. Females of Ophiomyia spencerella and O. phaseoli were distinct. However, overlap existed in male O. spencerella, O. phaseoli and C. horticola. In addition, there was overlap in female O. phaseoli, Tropicomyia vigneae and Liriomyza trifolii. The best discrimination in the male populations was obtained using the ratio of the proximal to the distal part of wing vein (M3+4). In the female populations, the best discriminating character was hind tibia length.

Out of 85 Bacillus thuringiensis strains isolated from Nigerian soils, 18 were larvicidal to Aedes aegypti, Culex quinquefasciatus and Anopheles gambiae. At 10−6 dilution of the final whole culture (FWC), the 11 most active strains, code-named GSC1, GSC3, GNA13, GNA14, OGL8, BUS4, BUS5, OBG1, OBG4, OBG8 and BAR3 produced mortality of 11.7–61.7% and 3.3–48.3% in Ae. aegypti and in C. quinquefasciatus fourth instars respectively. At 0.5 × 10−5 dilution of the FWC, the B.t. strains caused mortality in An. gambiae larvae ranging from 31.7 to 94.1%. All the 18 mosquitocidal isolates belonged to the subspecies israelensis, i.e. serotype 14. Microscopic examination revealed all the isolates to be typically Bacillus, with irregular or amorphous crystals of varying sizes.

The reproductive ability of gamma-irradiated Tribolium spp. (Coleoptera: Tenebrionidae) males was determined by studying their mating competitiveness when confined in various ratios with unirradiated males and females. Irradiated males of all the species studied competed favourably with unirradiated males for females. Competitiveness was significantly greater when males were irradiated soon after emergence (1-day old) than when they were older (10 days old). Infertility percentages increased as the proportion of irradiated males increased. The highest competitiveness was found in irradiated T.freemani and the lowest in T. destructor. Competitiveness also increased as the ratio of irradiated males increased.

A preliminary survey was conducted in coastal Kenya to assess the hosts of economically important tick species (Acari: Ixodidae) of domestic animals, as part of a training course for tick scientists from African research institutions. Ticks were collected from domestic animals in Kilifi and Kwale districts.

Eight tick species, namely Amblyomma variegatum, Boophilus decoloratus, B. microplus, R. appendiculatiis, R. evertsi evertsi, R. pulchellus, R. simus and A. gemma were identified. Further, more comprehensive surveys on the hosts, distribution and ecology of ticks of economic importance are recommended.

Two hundred seventy-three lines of the cultivated African rice species Oryza glaberrima Steud were screened in a paddy screenhouse at the National Cereals Research Institute, near Bida, Niger State, Nigeria for resistance to the African rice gall midge, Orseolia oryzivora Harris and Gagné, an increasingly important pest of lowland rice in Nigeria. Twenty entries which showed no galls in the screenhouse evaluation were retested under natural infestation in a gall midge-endemic field location near Abakaliki, Ebonyi State. Whereas the susceptible check variety, FARO 37, had 39.6 % of tillers infested 60 days after transplanting, damage in the test entries ranged from 0 to 3.7 %, an indication that they were all highly to moderately resistant to the pest. Greater host plant resistance is a central requirement for more effective management of O. oryzivora. Using resistance genes from O. glaberrima is a promising approach to achieving this.

The parasitoids Dinarmus basalis Rond. (Hymenoptera: Pteromalidae) and Eupelmus vuilleti Crwf. (Hymenoptera: Eupelmidae) develop mainly on relatively old larvae and pupae of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) found in cowpea seeds. Therefore, it is possible to consider biological control against C. maculatus using these natural enemies. The intrinsic rates of increase for C. maculatus and the two parasitoids were determined during the dry season in the sub-humid area of Bobo-Dioulasso, Burkina Faso, from January to July 1995. Functional response was also analysed for D. basalis and E. vuilleti. At the beginning of the dry season, the cowpea weevil and both its natural enemy species had limited intrinsic rates of increase, attributed to the relatively low temperatures and low relative humidity thatprevail during this period. In March, when temperature and relative humidity began to rise, conditions were optimum for their reproduction and development. Dinarmus basalis showed the higher intrinsic rates of increase and parasitism through the study period. Analysis of the functional response revealed that fecundity and potential for parasitism of both parasitoids were density-related and varied with climatic conditions. However, D. basalis showed a more efficient response. This study has shown that the variations of climatic conditions such as temperature and relative humidity during the dry season significantly influence the development and reproduction of C. maculatus and its parasitoids. Dinarmus basalis appeared to be the better biological agent in controlling C. maculatus.

Starch gel electrophoresis was used to compare eight loci in six enzymatic systems of 17 samples of the groundnut seed-beetle, Caryedon serratus (Ol.) (Coleoptera: Bruchidae) bred on five different host-plant species: Arachis hypogaea, Bauhinia rufescens, Cassia sieberiana, Piliostigma reticulatum and Tamarindus indica. The rate of polymorphism was 44.8%. The average genetic diversity (Hw) was 0.184. Allozyme variability analysis indicated that seed-beetles associated with P. reticulatum and groundnut, Arachis hypogaea were genetically similar, whereas other samples clustered according to their host plant species. Geographical distances less than 400 km were not decisive for the genetic structuring of samples associated with a given host plant.

The chitin synthesis inhibitor lefenuron [N-{2,5-dichloro-4-(1, 1, 2, 3, 3, 3-hexafluoropropoxy)-phenylaminocarbonyl}-2, 6-difluorobenzamide] was found to have a negative effect on the encapsulation responses of Spodoptera littoralis larvae towards supernumeraries of Microplitis rufiventris parasitoid. Superparasitised hosts fed on compound-free diet showed strong encapsulation reaction (ca. 40.8%) to surplus parasitoid larvae having scars of physical combat. Treated hosts exhibited a significant reduction in either capsule thickness or encapsulation rate to the excess parasitoid larvae. Even when a capsule was formed, it had a thinner haemocy tic layer than tha t of control hosts. Studies on the differential haemocyte counts showed that failure of treated larvae to encapsulate injured surplus parasitoid larvae could be attributed to the following factors: (1) disturbance in plasmatocytes-granular cells (GR) ratio, e.g. abnormal increase in GR levels possibly causing faint haemocytic reaction to injured parasitoid larva(e); (2) the parasitoid surface becoming less attractive to the granulocytes and plasmatocytes; (3) the haemocytes involved in capsule formation (granulocytes, plasmatocytes) losing their ability to spread out over the surface of parasitoid larvae; and (4) the blood cells of the treated host failing to recognise wounded larvae as foreign bodies. Reduced encapsulation capacity might be due to a secondary effect(s) of IGR treatment inducing a suppression of adhesive activity of the plasmatocytes. These results may be useful for improving our understanding of insect immune reaction and/or manipulating parasitoids activity against nonhabitual Parasitoida.

The ecdysteroid agonist KK-42 [l-benzyl-5(E)-2,6- dimethyl-1,5-heptadienyl] imidazole adversely affected the growth of Spodoptera litura and caused a delay in pupation. The compound also caused adult deformation, increased sex ratio in favour of males, and adversely affected the fecundity and fertility of emergent females. The ecdysteroid 20-hydroxyecdysone, identified by HPLC, was present in treated and control insects. Ecdysone was also detected in only the insects treated with 1 μg/larva KK-42.

A questionnaire survey of 100 smallscale cotton growers was conducted in two cotton-growing provinces of Mozambique to assess the constraints faced by the farmers in relation to the timing of insecticide application. The results showed that majority of the farmers started spraying too early (four weeks after germination) and were unaware that such sprays reduced the population of natural enemies of insect pests and might not lead to increased yields. The farmers applied an average of three sprays in the cotton growing season, about half of them according to pest observance and 41 % by following instructions of extension officers, but were constrained by the unavailability of insecticides and sprayers. Another constraint was lack of information on the timing of insecticide application. More than half of the farmers had suffered mild insecticide poisoning and needed more effective training on the judicious and safer use of insecticides, integrated with non-chemical pest management practices.

In laboratory experiments, pupae of the uzi fly, Exorista sorbillans Wiedemann (Diptera: Tachinidae), an endoparasitoid of the silkworm, Bombyx mori L. (Lepidoptera: Bombycidae) were subjected to UV-irradiation for different durations. Upon adult emergence, irradiated and control flies were crossed in all possible combinations and allowed to parasitise healthy silkworms. Adult emergence, fecundity and longevity of the resulting progeny were recorded. Progeny of irradiated E. sorbillans showed significantly reduced adult emergence, oviposicion period and hatchability. The reduction in fecundity was negatively correlated with the duration of exposure to UV radiation. The longevity of uzi flies of both the sexes was also significantly reduced.

Screen house studies on the incidence and yield losses in three cowpea (Vigna unguiculata) varieties, TV × 3236, Ife Brown and Ife Bimpe due to the leaf beetle Ootheca mutabilis Sahl were carried out. Artificial infestation was done at two growth stages of cowpea: the 5-leaf stage (2 weeks after emergence) and 4 weeks after emergence. Variety TV×3236 was found to be the least susceptible, while var. Ife Bimpe was the most susceptible to leaf beetle damage. Young plants were more susceptible than older ones.

Flowering was delayed in plants infested with beetles and the extent of defoliation had a pronounced effect on the yield of cowpea.

The percentage grain yield loss ranged from 19.48% to 59.77% depending on level of beetle infestation, variety and age of the plant at infestation.

An artificial diet for rearing the spotted bollworm, Earias vittella (Fabricius) was developed under laboratory conditions (temperature 27 ± 1°C, RH 60 ± 5% and 16:8 h scoto /photophase regime). The diet ingredients consisted of wheatgerm (5 g), seeds of cotton (Gossypium hirsutum L. var. Pusa 8–6) (50 g) and chickpea (Cicer arietinitm L. var. Kabuli)(35 g) as base materials along with agar-agar (15 g), dried yeast powder (8.0 g), methyl-p-hydroxybenzoate (1.0 g), l-ascorbic acid (1.2 g), sorbic acid (1.0 g), cholesterol (0.2 g), streptomycin sulphate (0.2 g), and multivitamin multimineral and vitamin E capsules (one each). After rearing neonates on okra for 3–4 days, the diet supported the growth and development of E. vittella successfully for eight generations. Larval development on this diet was completed in 11.9 ± 0.66 days against 11.64 days on the pest's preferred natural host, okra (Abelmoschus esculentus) Moench. The growth and developmental indices on the artificial diet for the eight generations are reported.

Teneral tsetse flies, Glossina morsitans morsitans (Mall) aged less than 32 h were divided into two groups and infected initially with Trypanosoma congolense IL 1180. Flies of group A were maintained on healthy rats and those of group B fed exclusively on parasitaemic rats, to ensure regular re-infection. Flies in group A recorded mesoprocyclic, metacyclic and vectorial competence (VC) index values of 0.65 ± 0.09; 0.73 ± 0.10 and 0.47 ± 0.11, respectively. The corresponding values for group B flies were 0.76 ± 0.08; 0.79 ± 0.08 and 0.60 ± 0.10. In group A, the mesoprocyclic and the VC indexes of the females were significantly higher than those of the males. In group B, no such significant differences were registered between the sexes. For both sexes taken together, the mesoprocyclic and the VC indexes of the tsetse flies of group B were more important than those of flies of group A. Males of group B revealed a higher VC index than that of group A males; no significant differences in this index were observed in the females of both groups.

Lepidopteran stemborers are major limiting factors in the production of maize and sorghum in Africa and Asia. Host-plant resistance and biological control are important components of an IPM programme and can effectively maintain pest populations below economic threshold levels, especially in low-input subsistence farming systems. When damaged by herbivores, plants produce allelochemicals which can attract natural enemies of the pest. These volatiles occur systematically throughout the plant and are different from those emitted in response to mechanical damage. We report evidence of plant volatiles-mediated differential reaction of parasitoid activity to sorghum genotypes. These volatiles could have a positive impact on the efficacy of stemborer parasitoids, leading to increased host finding or increased searching efficiency, thereby enhancing the suppression of stemborer populations. In a single-season case study, parasitoid activity was higher in stemborer-resistant genotypes than in susceptible ones and varied with crop age. Knowledge of such interactions should be explored and intensified by plant breeders and chemical ecologiste aiming at producing plant materials possessing appreciable levels of resistance to stemborers and able to encourage natural enemy activity in cereal-based ecosystems.