Acetylcholinesterase (AChE), arylesterase (AE), carboxylesterase (CE), and cholinesterase (ChE) activities were determined in six adult populations of the lesser grain borer, Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae) collected from grain warehouses in various areas of Punjab, namely Lahore (L), Sialkot (S), Wazirabad (W), Multan (M), Chkhawatni (C), and Karachi (K). The multiple forms of esterases were resolved by polyacrylamide gel electrophoresis (PAGE) and activities determined biochemically, using a spectrophotometer. All the strains had the same AChE activity except Sialkot strain, which had 46% more activity than the susceptible K strain. Similarly K, S, W, L, and C strains exhibited almost the same AE level, whereas the M strain showed 29% lower activity than K strain. The CE activity of L (352%), S (198%) and C (214%) strains and ChE activity of L (178%) and C (317%) strains were significantly higher than that of K strain. The total esterases of L, S and C strains showed respectively 152%, 63% and 73% higher activity than the susceptible K strain. The PAGE pattern of various esterases coincided with the biochemical analysis. The variable thickness of the bands in the gel indicated relative esterase induction that could be correlated with the development of resistance in R. dominica.

The volatility and mosquito repellency of the essential oil of Hemizygia welwitschii Rolfe (Laminaceae) and its prototype pharmaceutical formulations were examined and compared with those of a commercial mosquito repellent. At ambient temperature (28°C), neat Hemizygia oil had a volatility of 4.47±1.02 mg/cm2/ h for 15 hours, after which the rate declined. The oil evaporated at 200 μg/ cm2/ h from 10% w/w liquid paraffin solutions, and at 60 μg/ cm2/ h from soft paraffin during the first 20 hours, after which the decline in evaporation rate was generally bi-phasic. The oil demonstrated concentration-dependent repellency against the mosquito Aedes aegypti. Its liquid paraffin solutions (5% to 15% concentration) prevented up to 50% of starved mosquitoes from feeding on a blood meal for 6 hours. Lower concentrations were less effective and inhibited feeding for only 1 hour. A 15% w/w oil-in-water emulsion formulation of Hemizygia oil produced 55% feeding deterrence in the mosquitoes for 2 hours. Neither the solution nor the emulsion formulations of the oil provoked any adverse reaction on human skin.

The development, life table and intrinsic rate of natural increase of the reduviid predator Rhynocoris fuscipes (Fabricius) on Spodoptera litura Fab., Earias vittella Fab. and Corcyra cephalonica Stainton under laboratory conditions were constructed. Fecundity, longevity and minimum developmental period of the predator were dependent on the prey diet and decreased in the order: S. litura, E. vittella and C. cephalonica. The mean number of female progeny produced over the entire period (the gross reproductive rate) was 43.0, 37.5 and 32.5 on S. litura, E. vittella and C. cephalonica respectively. The net reproductive rate (Ro), intrinsic rate of increase (rc) and weekly multiplication rate were also highest on S. litura followed by E. vittella and C. cephalonica.

The population of coffee stemborers (Coleoptera: Cerambycidae) was estimated at six sites in south-west China using two capture-recapture models. Two sampling methods (simple and systematic random sampling), each at three sampling intensities (10, 20 and 30%) were employed for two-time capture attempts from which the capture-recapture estimates were calculated. Estimates from the models were compared with that of census data from the fields. When sampling intensity was 20%, satisfactory levels of accuracy were obtained using the two models. The level of accuracy of the estimates increased as damage rate and mean density of the insect increased. Accuracy was also increased with increasing the sampling intensity, when damage rate and density of stemborers in the plots were low.

A two-year survey was undertaken to determine the trypanosomosis risk of Egbe, a town in Kogi state of Nigeria, and its suitability for cattle raising. Tsetse flies were trapped using biconical traps and examined for trypanosome infection, and blood samples from cattle and goats were examined by blood film and haematocrit centrifugation technique (HCT) for trypanosome parasites. No infection was detected from the 152 Glossina palpalis palpalis and 52 G. tachinoides dissected over the period. Blood film examination of 181 cattle and 14 goats also gave negative results. Examination by HCT of 21 cattle from a local abattoir showed 14.3% Trypanosoma vivax infection, but the 10 resident cattle and 14 goats similarly examined were negative. The average age of the caught flies, determined by mean wing fray values (for males) and ovarian analysis (for females), was between 11 and 14 days, which is too low to sustain an infective population. Coupled with the absence of G. morsitans submorsitans, the most important vector of animal trypanosomosis in Nigeria, and the disappearance of large game from Egbe, our results would point to the area being a low trypanosomosis risk one.

To study the effect of temperature on the development and predatory behaviour of Culex (Lutzia) tigripes, immature stages of the predatory mosquito Culex (Lutzia) tigripes were reared at temperatures ranging from 12–37°C and provided Culex quinquefasciatus larvae as prey. Larval developmental duration decreased with an increase in rearing temperature until an optimum temperature of 30°C was reached. Above this temperature, the immatures developed slower. In contrast, pupal developmental duration decreased at temperatures above 30°C, being shortest at 32°C. The lower and upper threshold temperatures for larval development were around 12°C and 34°C respectively. Fourth instars were the most voracious and had the longest developmental time. The daily rate of predation increased with temperature, with more prey larvae being consumed at 30°C. Although they consumed more prey, Cx. tigripes larvae and pupae were smaller at high temperature. The increase in prey consumption during the entire larval developmental period at 20°C was attributed to a longer larval duration at this temperature. Developmental period and growth of male and female larvae reared at a particular temperature were not significantly different. Depending on temperature, each larva consumed between 160 and 229 Cx. quinquefasciatus larvae during its development. The implications of these findings to the possible use of Cx. tigripes for mosquito control are discussed.

The developmental potential of the palm aphid Cerataphis palmae Ghesquière (Homoptera: Pemphigidae) on three dwarf coconut varieties—Malayan dwarf red (Mdr), Malayan dwarf green (Mdg) and Malayan dwarf yellow (Mdy)—was studied in a screenhouse using leaf clip-on cages. Under similar temperature (30°C ± 1.13) and relative humidity (69.8% ± 1.63) conditions, the aphid expressed significant differences in fecundity, longevity and developmental period on the coconut varieties. The total developmental period on Mdr lasted 12.17 ± 0.76 days while on Mdg and Mdy it was 14.84 ± 0.63 and 13.83 ± 1.05 days, respectively. Thus the aphid population increased on the dwarf red variety over a significantly shorter period than it did on the other two varieties. Furthermore, fecundity and longevity of C. palmae on Mdr were significantly higher than on the Mdg and Mdy varieties (P < 0.01). These results indicate that Mdr supports C. palmae development better than the other two palm varieties.

The insecticidal activity of essential oils extracted by steam distillation from six aromatic plants from Togo, Cymbopogon schoenanthus (L.) Spreng., C. citratus (D.C.) Stapf., C. nardus (L.) Rendle, Lippia multiflora Moldemke, Eucalyptus citriodora Hook., Diplolofium africanum Turcz., was tested against the cowpea weevil, Callosobruchus maculatus F. Concentrations of 6.7; 10.0; 16.7 and 33.3 μ1/1 were evaluated. The chemical composition of the essential oils used was established by GC/MS analysis. Only C. schoenanthus oil showed significant insecticidal activity at 6.7 μl/1 oil (LC50 2.3 μ1/1). At concentrations higher than 33.3 μ1/1, all test plants showed similar insecticidal activity; more than 90% of the test insects died within 24 hours of exposure. Oviposition was also reduced significantly by the essential oil treatments.

Two studies were undertaken to determine the species composition of the phlebotomine sandfly fauna in the Mokolo region, an endemic focus of cutaneous leishmaniasis in northern Cameroon. The preliminary survey conducted in July 1994 using sticky paper traps recorded 843 sandfly specimens, all belonging to the two genera of the Old World sandflies, Sergentomyia and Phlebotomits. The species included S. (Sergentomyia) schzvetzi, S. (Sergentomyia) antennata, S. (Parrotomyia) africana and P. (Phlebotomus) duboscqi: From January 1996 to December 1996, a total of 3241 sandflies were collected using sticky paper traps. In this sampling, six out of the total of eight species recorded were of the genus Sergentomyia. In addition to the species recorded in the preliminary study, S. (S.) bedfordi, S. (Grassomyia) squamipleuris, S. (Sintonius), clydei and P. (Anaphlebotomus) rodhaini were sampled in 1996. This is the first report of S. squamipleuris ir Cameroon. The implications of this study to the transmission of cutaneous leishmaniasis are discussed with particular reference to P. duboscqi, a known vector of the disease in the region.

A list of 88 nominal taxa of mosquito species (Diptera: Culicidae) originally described from Uganda is given. The list includes 68 valid species, 7 subspecies, 6 varieties, and 7 synonyms, within 10 tribes, 14 genera, and 13 subgenera. All 3 subfamilies of Culicidae (Anophelinae, Toxorhynchitinae, and Culicinae) are represented. The type localities of the different species are updated for quick identification based on the present political boundaries within Uganda. The species stages that are as yet not fully described in the literature, and those species whose breeding habitats are unknown are indicated.

Wild Glossina austeni and G. pallidipes appear in many different populations. All conspecific flies possess similar surface hydrocarbons that include species-specific contact sex pheromones. Recently, evidence for a contact sex stimulant was found in the surface hydrocarbons extracted from female G. austeni. The bioactive hydrocarbon fraction contained alkanes and unsaturated hydrocarbons that were separated and analysed by GC/GC-MS. The structure and relative abundances of alkanes and alkenes from several populations of laboratory and wild collected specimens appeared to be similar.

Similarly, the alkanes of conspecific female G. pallidipes from several locations were analysed to determine differences and similarities with older, published work on the sex pheromone of the species. The components were analysed by GC-MS and were very similar across populations. If major components were compared, only minor variation was observed between females from Zimbabwe (wild), Amsterdam, ICIPE/Kenya, Kenya, Tanzania (wild), Uganda/Bristol and Arba Minch/Ethiopia. The absolute meaning of these differences is not known, since the activity of synthetic sex pheromones was shown conclusively against Wageningen and ICIPE males in 1984–1986 tests, although they were less active against Zimbabwe males.

A study was conducted to elucidate the effects of protein fractions isolated from maize (Zea mays L.) seeds on the development and survival of the Mexican bean weevil, Zabrotes subfasciatus (Boh.) (Coleoptera: Bruchidae). Maize seeds were fractionated into albumins, globulins, prolamins, glutelins and a residue and the bruchids reared on artificial seeds composed of susceptible background bean flour enriched with the different protein fractions. Survival (as indicated by LD50) and development (as indicated by WD50) of 20-day-old larvae of the bruchid were negatively affected by most of the fractions. The albumins and globulins were the most detrimental to Z. subfasciatus, significantly affecting both its survival and development.

Changes in the pattern of haemolymph polypeptides were studied to map the innate immune response of the malaria vector Anopheles stephensi (Diptera: Culicidae) to infection by the parasite Plasmodium yoelii yoelii. In addition, changes in the ontogenetic pattern due to glucose feeding, age, sex and gonotrophic cycle-related proteins were analysed. Six polypeptides were induced and 22 polypeptides disappeared due to glucose feeding during various stages of the mosquito's adult life. Five polypeptide patterns (91, 100, 108, 133 & 145 KDa) were found exclusively in female haemolymph. The changes in these polypeptide patterns have been correlated with sexual dimorphism in their feeding behaviour.

In total, 18 polypeptides were induced in the haemolymph of parasitised mosquitoes during different stages of development. Most of the polypeptides were induced in the early stages of infection, i.e. immediately after a bloodmeal. One polypeptide (25 KDa) was induced in all the stages. The expression of two polypeptides (32.5 and 70 KDa) on day 9 and one polypeptide (42 KDa) on day 15 was also enhanced following parasitism. The different induced proteins may help mosquitoes of different ages cope with parasite infection. The parasite evidently elicits immune responses in multiple tissues of the mosquito, including two epithelia which the parasite must traverse to complete its development. The mechanism of these responses and their significance in malaria transmission are discussed.

Two-dimensional gel electrophoresis was used to compare the protein profiles of two geographically isolated populations of the tick Rhipicephalus appendiculatus Neumann (Acari: Ixodidae) in Kenya. Most of the protein spots were common to both populations, but a number were specific to each population. Since proteins are encoded by genes, the presence of population-specific proteins suggests that there may be genetic differences between the two populations. It is proposed that some of these population-specific proteins might be related to the differences in susceptibility of the ticks to Tlwileria pnrva infection.

Commercial Bacillus thuringiensis (B.t.) Berliner products, namely Delfin®, Agree®, Halt® and Spicturin® were evaluated in the laboratory and on an intensively managed teak plantation for the control of the teak defoliator, Hyblaea puera Cramer (Lepidoptera: Hyblaeidae). A 2 g/litre concentration showed highly significant lethality against defoliator larvae, the early instars being more susceptible (99.8% mortality) than late ones (63.6–81.2% mortality). The order of effectiveness was Delfin = Agree > Halt > Spicturin. At 2 g/litre the B. t. preparations were as effective as at 0.07% (2 ml/litre) monocrotophos 36% when sprayed on one-year-old saplings in a plantation. However, at 1 g /litre concentration, monocrotophos 0.07% was superior to the B. t. products.

Methanolic extracts of stems and roots of silver fern, Cheilanthes farinosa Kaulf., (Polypodiaceae: Pteridophyta) incorporated into a semi-synthetic diet significantly extended the larval period, reduced pupal weight and adversely affected pupation of the cotton bollworm, Helicoverpa armigera (Hübner) (Noctuidae: Lepidoptera). Early third instars were more susceptible to the treatment than late third instars. A steroidal fraction (Rf 0.7) from the methanolic extract significantly reduced mean larval weight but did not affect pupation. A major ecdysteroidal component (R.t. 9.233 min.) was purified by reverse phase HPLC of this fraction, along with two minor components. The total yield of ecdysteroids was 564 mg/kg of shade-dried root and stem matter. Pooled HPLC fractions, when injected into final instars, resulted in dose-dependent effects on larval-pupal transformation. Adults emerging from treated larvae failed to lay eggs and were shorter-lived than their untreated counterparts.

The effect of potassium application to maize plants on the development, survival and fecundity as well as larval and pupal weight of Sesamia calamistis and Eldana saccharina were studied in the laboratory. Six different potassium treatments corresponding to 0, 30, 60, 60, 90, 120 and 150 kg K2O/ha were used. Potassium had no influence on larval and pupal developmental time or longevity of adult S. calamistis. The highest larval mortality was observed at 0 and at 150 kg K2O/ha. Increased doses (> 60 kg K2O/ha.) tended to reduce pupal survival. The lowest pupal weight was obtained at 150 kg/ha whereas fecundity was negatively related with potassium. The highest values of intrinsic rate of increase (rm) and net reproductive rate (Ro) were obtained with 60 kg K2O/ha and lowest with 150 kg K2O/ha. For E. saccharina, potassium had no significant effect on larval and pupal developmental time, larval survival, and pupal weight. The highest larval weight, pupal survival and fecundity as well as rm and Ro values were observed at 90 kg K2O/ha.

The polythene films used in manufacturing bipyramidal tsetse traps in the Central African Republic can exhibit slight variations in colours. Experiments using a new protocol that combines a Latin square design and two competing traps in the same experiment conducted on Glossina fuscipes fuscipes show that a iess intensely blue colouring decreases the attractiveness of the trap. Polythene is useful material for tsetse traps, but is necessary to verify that its colouring is homogeneous.

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.