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.

The influence of the host plants tobacco, chilli and brinjal on the susceptibility of Myzus persicae (Sulz.) to five OP insecticides was assessed. The order of toxicity of the insecticides to the aphids on tobacco was monocrotophos > demeton methyl > dimethoate > methamidophos > acephate, on chilli; methamidophos = monocrotophos > demeton methyl = acephate > dimethoate and on brinjal, methamidophos = monocrotophos > acephate > demeton methyl = dimethoate. Among the five insecticides, monocrotophos had the highest inhibitory potency in vitro as indicated by I50 and ka values, followed by demeton methyl, dimethoate, methamidophos and acephate. Electrophoretograms of homogenates of aphids adopted to chilli and brinjal showed a higher activity of the detoxicating enzyme carboxylesterase than found in aphids on tobacco.

Chilo partellus (Swinhoe) was first recorded in South Africa in 1958 and became a major pest of maize and grain sorghum. It has invaded the main maize producing areas in the Highveld Region, gradually competitively displacing the indigenous Busseola fusca (Fuller). Between 1980 and 1993 two egg, seven larval and two pupal parasitoids were introduced for biological control of Ch. partellus. Cotesia flavipes Cameron (Braconidae), Paratheresia claripalpis van der Wulp (Tachinidae), Tetrastichus howardi (Olliff) (Eulophidae) and Xanthopimpla stemmator Thunberg (Ichneumonidae) were released and recovered from the field. Recoveries were made up to a few weeks after releases but parasitoids failed to survive the winter and establish. The harsh winter conditions in the release sites, the long larval diapause period of Ch. partellus, lack of synchronisation between the development of the parasitoids and that of their host larvae, and absence of alternative host plants were identified as the main obstacles for the parasitoids establishment. It is concluded that the prospects of achieving any degree of biological control of stemborers in the Highveld Region with parasitoids from the tropics are poor. A parasitoid from a temperate zone of the USA, Macrocentrus grandii Goidanich (Braconidae), was introduced recently into South Africa and is currently reared on Ch. partellus in quarantine. Macrocentrus grandii stays dormant in its diapausing host, Ostrinia nubilalis (Hubner), during winter to emerge in spring. Because of its ability to diapause in winter it is hoped that after releases, M. grandii will establish on Ch. partellus in the Highveld Region of South Africa.

Lipids were extracted from the plasma and gonads of fourth and fifth instars and adults of Dysdercus koenigii (Heteroptera: Pyrrhocoridae). Thin layer chromatography of the extracts revealed fractions of free fatty acids (FFA), monoglycerides (MG), diglycerides (DG), triglycerides (TG), phospholipids (PL), free cholesterol (FC) and esterified cholesterol (EC). There were distinct differences in the lipid profiles within sexes for both tissues during development. Phospholipid from female plasma showed significant fluctuation during development, while that from males remained constant. In female gonads, PL levels increased significantly from the fouth instar to the fifth instar. Monoglycerides were detected only in adult male plasma and adult female gonads, at very low levels. Plasma DG in males was found to increase significantly during development. Maximum gonadal DG was recorded in male fourth instars and female fifth instars. Triglycerides in female plasma declined from the fourth instar to the adult stage. In contrast, TG in gonads increased significantly in the fifth instar of both sexes. Plasma FFA of both sexes fluctuated during development. Free cholesterol was detected only in adult male plasma. Plasma EC increased from the fourth instar to the adult stage in males, and it was highest in gonads of fifth instars of both sexes.

Wild-caught Xenopsylla brasiliensis from Kibwawa village, Chunya District, in south-west Tanzania were colonised in the laboratory and their offsprings used for determining the baseline susceptibility levels of the strain to DDT. A total of 120 fleas were tested with each concentration of DDT, using the techniques described by the WHO Expert Committee on Insecticides (1970).

Several filial generations were selectively raised, using DDT as a selection pressure. They were tested with various concentrations of the insecticide and their dosage–mortality regression lines compared with that of their parents.

About 5% of the parental generation (normal population) survived 1 hr exposure to 4% DDT. The LC50 of this population was 0.79% DDT. The mortality rates of the successive filial generations decreased gradually; their dosage–mortality regression lines moved to the right; and the slopes of these lines decreased. LC50s of F1, F2 and F3 were 1.6, 1.9 and 3.1% DDT, respectively. The highest DDT concentration (4%) killed 21.1 and 18.3%, of F4 and F5, respectively.

It was generally concluded that DDT resistance was present in the population, and that the selection pressure (DDT) was responsible for increasing the level of this resistance in the laboratory.

The diversity of visitors to flowers of the grass Brachiaria ruziziensis R. Germ and Evrard is very low in Ngaoundéré, Cameroon. Bees (Hymenoptera) and syrphids (Diptera) were observed gathering pollen, and each insect group had its own strategy depending on the prevailing environmental conditions. Syrphids are early-morning flower visitors and take time to feed on wet pollen. They visit flowers from 0630 h when the relative humidity is higher than 80% and temperature lower than 25°C. Bees gather dry pollen from 0930 h when the relative humidity is <50% and temperature>30°C, and carry it to the nests for feeding.

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.

At Alemaya in eastern Ethiopia, tef (Eragrostis tef) was found to be attacked by a complex of seven shootfly species, five species belonging to the family Chloropidae and two to Muscidae. Atherigona hyalinipennis (Diptera: Muscidae) was economically the most important species in the shootfly complex of the crop. It caused 42–58% damage to growing panicles in different varieties of tef, which resulted in an estimated loss of 378–522 kg/ha. The average incubation period of eggs, developmental periods of larvae and pupae of A. hyalinipennis were 3.0, 12.7 and 9.6 days respectively, and the total life cycle was completed in less than a month in the laboratory. Larval parasitism by Neotrichoporoides nyemitawus ranged from 6.7 to 18.5%. Peak activity of A. hyalinipennis in the region was in August to September.

The homopteran bug Cofanaspectra (Distant), also known as the white leafhopper, is abundant in rice-growing areas of India (West Bengal, Northeast and southern states) and considered as a minor pest of paddy. The proportion of Cofanaspectra and the endoparasitoid Halictophagus australensis Perkins varied between months and demonstrated peak abundance during March to May and October to December, which corresponded with the rice cropping periods boro (winter crop) and aman (monsoon crop), respectively. There was a negative correlation between the influence of environmental factors (air temperature, rainfall and relative humidity) and the abundance of normal and parasitized C. spectra. The proportion of parasitization by H. australensis varied with the relative abundance of C. spectra. The effect of stylopization on C.spectra by the Strepsiptera may be one of the factors attributable to the suppression of the population levels of the paddy pest.

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.

The recent development of geographic information systems (GIS) provides new avenues for analysing spatial patterns in insect populations. Field survey data, along with GIS and statistical models were used to predict the distribution of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) and Cotesia flavipes Cameron (Hymenoptera: Braconidae) in Ethiopia. The results obtained suggested that the distributions of Ch. partelhis and Co. flavipes were affected by rainfall and temperature. The predicted distributions of Ch. partellus and Co. flavipes were similar. Validation of predicted values is discussed.

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.

The corn earworm damage to seven maize cultivars TZB, TZPB, WYI, 096EP6, Farz 25, ‘Kewesoke’ and Local White, was assessed during the early and late cropping seasons of 1980 and 1981 at Ikenne and Ilora located in the rain-forest and derived savanna zones, respectively. The effectiveness of dimethoate and permethrin in controlling the earworms was evaluated. All the cultivars appeared susceptible to earworm infestation in the two ecological zones. Infestation was consistently and significantly higher in the early season and also in the rain-forest zone. It ranged from 71.5 to 86% in the early and from 28 to 36.8% in the late seasons, respectively, at Ikenne. At Ilora, infestation ranged from 53 to 82% and from 20 to 75% in the early and late seasons, respectively. Mussidia nigrivenella and Heliolhis armigera were the dominant species recorded damaging the grains.

Earworm infestation was significantly lower on plots treated wtih three applications of 0.05 and 0.1% a.i. permethrin at weekly intervals than on plots that received the same dosages and sprays of dimethoate and the control. Maize yields were significantly higher on permethrin-treated plots. The lower dosage of permethrin is recommended to reduce chemical residue on maize grains.

The virus Rhabdionvirus oryctes Huger was tried against the root and stem borer of the cashew (Anacardium occidentale L.) in Sri Lanka by pouring a virus suspension into the galleries, releasing virus-infected adults and placing virus-mixed sawdust at the base of the infested stem. Results obtained after several surveys showed that the sawdust technique gave more positive results. The establishment and infection of the virus in the beetle population accounted for a reduction in the beetle damage to the tree in certain pockets of the cashew plantation.

Nearly 8 years of intermittent treatments with temephos on the lower Volta River at Senchi Rapids, Ghana, produced no change in the susceptibility of larvae of the S. damnosum complex to temephos [Abate (R)]. In contrast, 14 months of temephos treatment in southern Ivory Coast produced resistance.

This difference can be explained by the relatively weak selection pressure exerted by the intermittent treatments on the Volta River and the frequent changes in the composition of the population as shown by cytotaxonomic identification of the larvae.

Full-grown pupae Agrotis ipsilon were irradiated with 5 or 10 krad and crossed with unirradiated female. The F1 progeny were more sterile than parents. Percentage of mated female of F1 was greatly reduced while the mating frequency was increased. Less inseminated females were among the F1, particularly when the female inherited the sterility. The mortality among larvae of the F1 was high and dose-dependent, and that among F2 larvae was even higher. The sex ratio of the F1 progeny was altered in favour of male, while that of the F2 was normal. 10 krad for P1 male was sufficient to inhibit hatching of the eggs produced by F1 adults.