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

Egg-masses of Simulium damnosum s.l. were investigated to explain the frequent presence of undeveloped eggs in the lower layers. Natural development within egg-masses depended on whether eggs were laid (a) all at once or (b) were added to on consecutive evenings. In the field where the development of eggs from situation (a) was followed, top layer (TL) eggs hatched in 2 days when unexposed bottom layer (BL) eggs were still white. BL eggs uncovered 12 hr after oviposition were undeveloped, then hatched in 3 days. BL (a) eggs uncovered after 5 days were still untanned and undeveloped but were not further investigated.

In the laboratory, portions of egg-masses—intact or with the BLs exposed—were incubated in Petri dishes with and without preceding KOH egg separation treatment, or in flowing water. Other samples of BL eggs were incubated at different O2 levels. In Petri dishes, most TL eggs hatched within 24 hr of setting up but exposed BL eggs hatched (if at all) after much delay in 6–14 days. No unexposed BL eggs hatched even after TLs above them had done so. Transfer to flowing water or KOH treatment increased hatching and reduced the delay. Hatch rates of exposed BL eggs rose from 2.7 to 63% with increased O2 levels.

Implications with regard to laboratory culture and control operations are discussed. Mortality of covered eggs could be a potent population regulating factor within and perhaps even between species of the S. damnosum complex.

Zea mays L. and Rottboellia exaltata L. were the main graminaceous plant species infested by Eldana saccharina Walker, the major pest of sugar-cane in southern Ghana. Other stem-borers of sugar-cane, Sesamia botanephaga Tams and Bowden, Sesamia penniseti Tams and Bowden, Sesamia calamistis Hampson and Chilo zacconius Bleszynski, were recorded on Zea mays, Echinocloa pyramidalis (Lamk.) et Chase, Rottboellia exaltata, Panicum maximum Jacquin and Oryza sativa L.

All the stem-borer populations except E. saccharina on Rottboellia exaltata increased on their host plants. Sesamia and Chilo species were present from January to December on Echinocloa pyramidalis. It is concluded that these alternative host plants provide a potential source of stem-borer infestation on sugar-cane at Asutsuare in southern Ghana.

Sun-dried guava (Psidium guajava L.) and eucalyptus (Eucalyptus globulus L.) leaves were evaluated as repellent and toxic materials against the rice weevil, Sitophilus oryzae L., and the granary weevil, Sitophilus granarius L. under laboratory conditions. LC50 values of sun-dried guava and eucalyptus leaves admixed with rice grains against S. oryzae were 2.251 and 4.140g leaves/100g rice grains, respectively, while they were 2.278 and 4.857 g leaves/100 g rice grains in the case of S. granarius, respectively. Guava leaves were more toxic for both species than eucalyptus leaves. Eucalyptus leaves were more repellent than guava leaves.

Both test materials at 15 g/100 g depressed the progeny development of the test insects.

Lufenuron, N–[2, 5–dichloro–4–(1, 1, 2, 3, 3, 3– hexafluoropropoxy) –phenylaminocarbonyl]–2, 6–difluorobenzamide, a novel acylurea insect growth regulator, exerted significant sublethal effects in larvae, pupae and adults of the diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae). Second, third and fourth instars were treated at their respective LCM using a standard 'leaf–disc dip' method of bioassay. Sizes and weights of pupae from the treated lots were significantly reduced but larval and pupal durations remained unaffected. All the pupae formed from larvae treated as fourth instars were deformed and produced no adults. Only 38 and 14% of adults emerged from the pupae formed following treatment at the second and third instar, respectively, as compared to 88–92% adult emergence in the controls. Apart from significant reduction in body length, some adults from the treatments had fringed and twisted wings which prevented normal flight. IGR treatment also resulted in pronounced reduction in fecundity (up to 10.2 eggs per female in comparison with 135.8 per female in the control) and oviposition periods (up to 3.2 days in comparison to 7.8 days in the control). Field trials to investigate the management of P. xylostella using lufenuron are recommended.

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.

Genetic analysis of sorghum resistance to stem-borers was performed in a 6 × 6 diallel cross. The results indicated that resistance to stem-borers is polygenically inherited. F1 hybrids did not differ significantly from mid-parental values suggesting intermediate inheritance. However, resistance was partially dominant to susceptibility. Combining ability analysis showed that resistance to primary damage, i.e. % ‘dead heart’ was governed by both additive and non-additive type of gene actions while secondary damage, i.e. % stem tunnelling was governed predominantly by additive gene action. It was noted that the inheritance patterns of primary and secondary damage were different. Tunnel length showed positive correlation with the number of larvae per plant and negative association with plant height, but had no correlation with grain yield per plant. On the basis of larvae recovered from the tunnelled plants, Chilo partellus was found to be the predominant stem-borer species followed by Sesamia calamistis, Eldana saccharina and Busseola fusca. Significance of genetic studies of host plant resistance in deciding breeding strategies for insect resistance has been discussed.

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.

The biology of Thrips nigropilosus Uzel was studied in a laboratory. The life history was examined at 20°C as well as the effect of temperatures on its life cycle at 12, 20, 25 and 30°C with fixed 70% r.h. The thrips pass through egg, two larval instars, prepupae and pupae to become adults. The development of these pre-adults occur on the pyrethrum plants except that prepupal and pupal stages occur in the soil. The emerged adults display sexual dimorphism, with lower ratio of male to female (2:11) and adult longevity range of 1–21 days.

The thrips development duration decreased with increasing temperatures. When expressed as rates, it was found out that faster development occurred for the second larval and pupal instars than other stages with an increase in temperature. The optimum temperature for the thrips development was 20°C, mortality being higher at other temperatures.

Larval establishment and feeding site selection of Eldana saccharina Walker were studied on maize (Katumani Composite B) and sorghum (Serena). These parameters were defined as the location within the plant of the larva 7 days after hatching; and feeding activity was measured by the extent of stalk tunnelling. In naturally infested maize, more larvae settled in the basal section of the plants between second and fifth node/internode, and in sorghum they settled between fourth and seventh node/internode. In the artificially infested plants of both crops, larvae settled in the middle section of the plant mainly between fourth and seventh node/internode. The neonate larvae first settled in the leaf sheath until they were third instars when they entered the stalks. However, in sorghum stalk entry was limited by stalk wall toughness and waxes on the stalks.

The extent of stalk tunnelling indicated that in maize larval feeding is highest in the internodes whereas in sorghum it is in the peduncles.

Scanning electron microscopic examination of the egg shell and associated structures of Eocanthecona furcellata (Wolff.) (Hemiptera: Pentatomidae) reveals a distinct pattern of structural elements, viz. microsculpture of the chorion, pseudoperculum, egg burster and aeromicropylar processes. The egg shell has a highly decorated chorion with a structural difference at both the anterior and posterior ends. A reticulate type of microsculpture with varying sizes of spine-like projections measures 4.02 ± 0.06 to 8.12 ± 0.05 μm and forms an asteroid-like shape at the anterior pole, while the surface at the posterior end has elongated striations over the chorion measuring 72.00 ± 0.074 μm. The pseudoperculum of the egg shell is a circular lid measuring 518 ± 11.43 μm in diameter. During hatching the line of rupture follows the micropylar ring, and this sometimes extends beyond the ring of micropylar processes. An inverted T-shaped black egg burster measures 202 ± 4.63 μm in length, is well developed and can be seen prior to hatching within a thin and transparent egg shell. It is a median sclerotised part of embryonic cuticle. The aeromicropylar processes are situated at the anterior pole of the barrel-shaped eggs. There are 26–28 aeromicropylar processes arranged in a circle at almost equidistance and each micropylar process is slightly curved opposite to the pseudoperculum lid with a bulbous end at the apex. The aeromicropylar processes are 25.40 ± 0.083 μm in length and 3.02 ± 0.07 μm in width. Each micropylar process has a central canal for the passage of sperm whereas the rest of its body is porous, and allows respiratory interchange.

Adults of various phlebotomine sandfly species were obtained from leishmaniases endemic foci in Kenya using several trapping methods. Ten species were successfully reared from egg to adult in the laboratory; and large colonies of Sergentomyia schwetzi, S. bedfordi, S. ingrami, S. antennatus, S. adleri, S. garnhami, Phlebotomus duboscqi and P. martini established. Generally, the development of Phlebotomus spp. from egg to adult took longer (54.7–57.2 days) than Sergentomyia spp. whose developmental time with the exception of S. garnhami, varied between 36.5–42.3 days.

Busseola fusca Fuller is one of the major lepidopteran stemborers of maize and sorghum in Africa. Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) is an indigenous, gregarious larval endoparasitoid that attacks mid- to late-instar stemborer larvae, which is reported to be one of the most important larval parasitoids of B. fusca in many countries in sub-Saharan Africa. Previous work has shown that two biotypes of C. sesamiae occur in Kenya which express differential abilities to develop in B. fusca. A biotype from western Kenya successfully develops in B. fusca, while a biotype from the eastern coastal area does not. We treated fourth-instars of B. fusca with calyx fluid from C. sesamiae from western Kenya (Kitale) before offering them to C. sesamiae from the Coast (Mombasa) for oviposition, and found that the eggs were not encapsulated. This suggests that factors in the calyx fluid of C. sesamiae from the western Kenya biotype were responsible for suppressing the immune system of B. fusca. We speculate that polydnaviruses in the calyx fluid were involved in disarming the host immune system, and that the polydnaviruses in the two biotypes are genetically different.

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 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.

The first report on the entomopathogenic fungi in the tropics dates back to 1853. Despite their variety, little attention has been focused on their incidence on agricultural pests. Studies over the last 20 years in the tropics have revealed that entomogenous fungi (Deuteromycetes and Entomophthorales) may play an important role in natural control of arthropod populations. Therefore, the use of insect pathogenic fungi as pest control agents is promising.

An important consideration in developing an entomopathogenic fungus as a mycoinsecticide is the selection of the correct and well-adapted strain. New techniques in biotechnology will help in developing methodology for mass production and formulations. Other factors which can be considered, and which may be determinants on the potential of insect pathogenic fungi include the environmental conditions and cultural techniques (e.g. intercropping, planting density, irrigation). The cultural techniques can result in change of the environment favourable to the disease.

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.

Earias vittella (Fabricius) feeds on some malvaceous plant species, but has never been reported to attack Thespesia populnea Cav., even though this plant belongs to the same family. The factors responsible for the failure of E. vittella to establish on T. populnea were, therefore, studied. When whole fruits or fruit pericarps of this plant were provided as larval food, larvae failed to develop and none of them pupated. However, on developing seeds of these fruits, larval growth and development were normal and comparable to those of larvae reared on developing seeds of the most favoured host plant, Abelmoschus esculentus Moench. Ether extracts from fruit pericarps exhibited antifeedant and antibiosis activity against this insect. Ether as well as ethanol extracts affected oviposition to some extent. In a choice situation, significantly less eggs were laid on treated than on untreated okra fruits. However, in a no-choice situation most of the eggs were laid on treated okra fruits.

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.

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.