Cowpea, Vigna unguiculata (L.) Walp., is susceptible to a wide spectrum of insect pests from seedling to harvest as well as in storage. Insecticide use has been the most commonly adopted method for the control of cowpea pests. However, due to the deleterious effects of insecticides on man, livestock and the environment, research over the years has been focused mainly on developing resistant/tolerant cultivars as a vital component in the integrated management of cowpea pests. This approach has, however, recorded varying degrees of success, due in part to the multiple and often overlapping pest complex attacking at different phenological growth stages of the crop.

In spite of the progress in the utilisation of insect-resistant cowpea varieties, the use of resistance as a control tactic has by no means been fully realised. There are many important cowpea insect pests for which resistant varieties are not yet available for commercial cultivation. Where resistant varieties are available for a given insect, these varieties may not be widely planted because of their unsuitability to local conditions.

In this paper, the status of host plant resistance research in cowpea is reviewed and some novel approaches aimed at solving its seemingly intractable pest problem are proposed, based on the state-of-the-art scientific and crop biotechnological development. The proposed framework for orientation of cowpea resistance research should ensure yield stability and sustainability for the resource-poor, smallscale farmers in Africa.

The oviposition behaviour of the cowpea weevils, Callosobruchus rhodesianus (Pic.) and Callosobruchus maculatus (F.) on clean and egg-laden adzuki beans was examined in choice and no-choice experiments. The oviposition rate of C. maculatus was greater than C. rhodesianus in both experiments. Both weevil species were able to distinguish between clean and egg-laden beans. Discrimination by both species was greater against seeds with 12 eggs than with 6, regardless of which species had previously laid eggs. There was a weak indication that the presence of C. maculatus eggs at high densities might reduce the oviposition rate of C. rhodesianus.

This paper justifies the need for a single taxonomic work providing a key to the common mealybugs of tropical Africa, and provides such a key for identification of some adult mealybugs of Central Africa. If users find that their specimens do not fit into the key, then the specimens are probably other species and should be sent to an expert for identification.

A chromatographically enriched fraction designated Fraction B from dry fruits of the plant Melia volkensii (family Meliaceae) was evaluated with the objective of determining its toxic and growth inhibiting effects on the larvae and adults of Culex quinquefasciatus mosquitoes. The fraction was purified from a crude methanolic extract by cold precipitation and elution of the precipitate dissolved in a hexane-ethyl acetate solvent system through a silica gel column. Larval treatments involved rearing the larval stages in water containing the fraction at concentrations of between 5 and 200 ppm. The LC50 for this fraction was found to be 34.72 μg/ml in 48 h. Second instar larvae were found to be more susceptible to fraction B when compared to fourth instar larvae. All fourth instar larvae that survived the treatment moulted into larval-pupal intermediates that were short-lived. The extract was also found to be an oviposition deterrent at a concentration of 20 ppm and above. It is concluded that M. volkensii extract has potential in the control of Culex quinquefasciatus.

The already known benzoquinone, embelin (mixed with rapanone), and two new benzoquinones, myrsinone and myrsinaquinone, were isolated from the Myrsinaceae plant, Rapanea melanphloes (L), Mez. All the three compounds showed antifeedant activity when bioassayed on nymphs of the desert locust, Schistocerca gregaria (Forsk). They also inhibited growth of second-instar larvae of mosquito Aedes aegypti at low doses, and had acute lethal effects at higher doses.

Azadirachtin, the principal active ingredient of neem seed and aqueous neem seed extracts (ANSE) reduced food intake and utilisation efficiency in the penultimate instar level of the African armyworm (Spodoptera exempta) when applied either topically or mixed with the diet of the insect. These observations reflect interference of neem with centres in the insect that regulate feeding and metabolism. The decreased food utilisation efficiency in treated insects indicated higher metabolic costs as they had to direct some energy into dealing with neem deposits in their bodies rather than biomass production.

The effect of protein fractions isolated from cereal grains on the development and survival of the bean weevil, Callosobruchus maculatus, was investigated using wheat, rice and maize. These cereals were fractionated into albumins, globulins, prolamins, glutelins and a residue. The fractions were incorporated in artificial seeds which were infested by C. maculatus. Survival (as indicated by LD50) and development (as indicated by WD50) of 20-day-larvae of the bruchid were negatively affected by most of the fractions. Rice globulins were the most detrimental and affected both the survival and development of the larvae, while wheat albumins and globulins had a stronger effect on larval development than on survival. A previously isolated maize α-amylase/trypsin inhibitor showed an LD50 of 1.5% to Callosobruchus maculatus.

The effect of photoperiod on the haemolymph protein profile in the silkworm, Bombyx mori L. larvae was investigated at photoperiod treatments of light to dark (L:D) ratios of 13:11 (control), 24:0, 18:6, 12:12, 6:18 and 0:24 hours using fifth instar larvae. The intensity of protein bands in haemolymph extracts from larvae was measured with a densitometer. The intensity was highest in the haemolymph from larvae in the 24:0 (L:D) h photoperiod. Strongly reactive antigens of SP-1 and SP-2 and weakly reactive bands of storage proteins for both male and female larvae were observed in the 24:0 (L:D) h photoperiod.

The effect of four biologically active and naturally occurring plant quinones, namely maesanin, maesaquinone, embelin and juglone on the respiration of mitochondria isolated from Glossina morsitans morsitans, Schistoscerca gregaria and Periplaneta americana was investigated. The rate of oxygen consumption by the mitochondria was measured using an oxygen electrode. Maesanin inhibited the mitochondrial electron transport chain at a level before cytochrome C whereas maesaquinone and embelin uncoupled the mitochondria. Juglone inhibited respiration in G. m. morsitans mitochondria and uncoupled those of S. gregaria and P. americana.

This study was conducted to identify the individual biochemical factors involved in the resistance observed in a few Mexican bean accessions against the bean weevil, Acanthoscelides obtectus (Say) (Coleoptera: Bruchidae). Soluble proteins from different bean genotypes were separated by fractionated acetone precipitation. Insects were reared on artifical seeds composed of a susceptible background bean flour enriched with the different protein fractions. At low doses (2% w/w), the 0–20% and 20–40% acetone fractions of the resistant bean accessions G 12954 and G 12880 inhibited larval growth of the bean weevil, but not of a related species, the Mexican bean weevil, Zabrotes subfasciatus (Boheman). The 0–20% fraction caused the highest mortality of first instar larvae. The 60–80% acetone fraction contains general resistance factors, like α-amylase and protease inhibitors, which when enriched in artifical seeds led to a strong depression of insect growth for resistant and susceptible bean accessions alike. These factors should also be taken into account in breeding for multigenic, durable resistance, in order to exploit the synergism between general and specific resistance factors.

The development of Helicoverpa (= Heliothis) armigera (Hb.) (Lepidoptera: Noctuidae) on foliage, squares and bolls of four cotton cultivare [G 27, HD 167 (Gossypium arboreum), H 777 and H 974 (G. hirsutum)] and one hybrid (HHH 81) was studied under controlled conditions. The results indicated that some biological parameters were influenced only by plant parts and not by cultivar/hybrid. The larvae died as first instars when reared on the foliage of cv. G 27 and HD 167. Irrespective of cultivar, the larvae and pupae weighed more when the larvae were reared on cotton bolls than on squares and foliage. The larval and pupal periods were shortest for larvae reared on bolls, followed by squares and foliage. The fecundity of the female was highest when the insect was reared on bolls, followed by foliage and squares. The longevity of the female moth was highest in insects reared on bolls, followed by insects reared on squares, and on foliage. The longevity of the male moth was not influenced by rearing on the different plant parts. The duration of the life cycle was shortest for insects reared on bolls, followed by squares and foliage.

The response of two cotton varieties (TCH 1002 and 77/10) and two hybrids (TCHB 213 and DCH 32) to damage caused by the American bollworm, Helicoverpa armigera was evaluated under two spacings and three fertiliser levels each. Variety TCH 1002 was less damaged than 77/10, whereas between hybrids, DCH 32 was less preferred than TCHB 213. Damage was higher when the varieties were grown at a spacing of 50 × 20 cm and the hybrids at a spacing of 120 × 45 cm compared to 75 × 30 and 120 × 60 cm, respectively. Increasing the amount of fertiliser applied did not have any significant effect on damage caused by the pest. Tannin and gossypol contents were found to influence levels of damage caused by H. armigera. A combination of high tannin and gossypol resulted in reduced damage. The highest tannin content in varieties was recorded in leaves of TCH 1002 grown at a spacing of 75 × 30 cm, with a fertiliser level of 120:60:60 NPK kg/ha. The highest gossypol content was recorded in flowers of TCH 1002 under similar spacing and management levels. In the hybrids, the highest tannin and gossypol contents were recorded when DCH 32 was grown at 120 × 60 cm spacing with a fertiliser regime of 120:60:60 NPK kg/ha. Cotton was damaged to a greater extent when grown at a closer spacing. Increasing levels of nitrogen resulted in higher damage levels.

An investigation was carried out on the effects of three patterns of sorghum (Sorghum bicolor) and cowpea (Vigna unguiculata) intercrops on larval establishment of the spotted stemborer, Chilo partellus, on sorghum at different growth stages. The intercrop patterns were: sorghum sown simultaneously with cowpea, sorghum sown 2 weeks before cowpea and sorghum sown 2 weeks after cowpea. Sole sorghum and sole cowpea were controls. Sorghum plants were infested at 4, 6 and 8 weeks after emergence (WAE). Ten days after infestation, the infested plants and their immediate neighbours in the same row were uprooted and dissected. The number of larvae recovered and their stages of development were recorded. Some predatory arthropods were monitored by direct egg counts and use of pitfall traps. Grain yields were recorded at harvest to determine land productivity. Larval establishment was significantly (P < 0.05) higher on sorghum plants in sole crop than in intercrops; it was also higher on sorghum plants infested 6 WAE than on other dates. More C. partellus larvae were lost from sorghum sown after cowpea than in other cropping patterns, and more larvae were lost from sorghum plants infested at 4 WAE than on other dates. More predatory arthropods were observed in cowpea cover compared to those found in sole sorghum—the arthropods may be responsible for the observed loss in C. partellus larvae in the intercrop. Land productivity was higher in sorghum sown simultaneously with or after cowpea than in other cropping patterns. Thus, intercropping increased larval loss in C. partellus and improved productivity.

Some aspects of the biology of Callosobruchus maculatus (F.) on three varieties of bambara groundnut, Voandzeia subterranea (L.) Thou and a local brown cowpea variety, Vigna unguiculata (L.) Walp were studied under ambient laboratory conditions. Egg hatchability of C. maculatus was above 90% on all the legume varieties. The mean developmental period of C. maculatus ranged from 23.7 days on cowpea to 28.5 days on the Piele kargu variety of groundnut. The percent emergence of C. maculatus ranged from 61.1% on var. Piele kargu to 89.5% on var. Piele balgu. There was a significant difference (P < 0.05) between the damage caused to the brown cowpea and the bambara groundnut varieties. However, there were no significant differences (P > 0.05) in damage among the three groundnut varieties. In experiments to assess the insecticidal potential of three plant materials against C. maculatus, Azadirachta indica (neem) seed powder showed a higher efficacy than both Citrus sinensis peel powder and the powder of Chromolaena odorata leaves. At 1.0 g per 40 g of legume seed, it was twice as effective as Ci. sinensis and Ch. odorata over a period of 40 days.

The electrophoretic variation of four enzymes of wild Anopheles pharoensis in Mwea Irrigation Scheme, Kenya, was studied between 1987 and 1988. The enzyme loci examined were aldehyde oxidase, a-glycerophosphate dehydrogenase, β-hydroxyacid dehydrogenase and lactate dehydrogenase. All the loci examined were dimorphic. A mean heterozygosity (H) of 0.341 was obtained, which is comparable to values for other mosquito species. The allelic frequencies were in genetic disequilibrium compared to Hardy-Weinberg predictions. It is proposed that there may be more than one species in the taxon Anopheles pharoensis.

Silkworm larvae infected transovarially with Nosema bombycis were fed with an aqueous suspension of Bavistin (50% carbendazim w/w) at 2 and 3% concentrations. The treatments increased the survival of worms and reduced the pebrine infection in the lot significantly, although complete elimination of infection was not observed. Significant beneficial effects of the treatments at 2 and 3% were also observed with respect to larval, cocoon and cocoon shell weights and cocoon to shell ratio. However, treatments with Bavistin at 4% concentration produced an adverse effect on cocoon characters.