Local isolates of Bacillus thuringiensis were isolated from infected rice stemborers, soils, rice bran and rice mill dust. Of 83 isolates serotyped by B. thuringiensis H-antisera, 13 serotypes were identified. Those serotypes were assigned to B. thuringiensis of subspecies canadensis, galleriae, kenyae, kurstaki, neoleonensis, aizawai, alesti, entomocidus, tochigiensis and tolworthi. Three serotypes, 3a:3c:3d, 5a:5b/21 and 17/27, were unnamed and portend to be new subspecies. Morphological studies of delta-endotoxin or crystal protein of each subspecies showed significant differences in size and shape. Bipyramidal crystals, spherical and cuboidal crystals and the combinations of these structures were observed. Toxicity of sporulated cultures and isolated crystal proteins of B. thuringiensis strains to five species of economically important insects were determined using diet incorporation bioassays. Extracted crystal proteins from certain B. thuringiensis subspecies were highly toxic to some insect species. These have the potential of providing alternative strategies for utilizing B. thuringiensis for controlling insects.

Polyacrylamide gel electrophoresis was used to study esterase variation in a population of B-type Bemisia tabaci (Gennadius). A total of six esterases was identified within an overall B-type pattern. However, both qualitative and quantitative variation in some of these esterases gave three clearly defined phenotypes. One of these lacked esterase E0.14 which until now has been the key band used to classify B-type strains electrophoretically. A strain homozygous for the E0.14 null allele (B-Null) retained the ability to induce squash silverleaf, a plant physiological disorder which hitherto has only ever been associated with whitefly strains possessing this band.

Eleven strains of Bemisia tabaci (Gennadius), including a laboratory susceptible strain, were bioassayed as adults with three organophosphorus (OP) insecticides, three pyrethroids and one OP/pyrethroid combination. The contemporary strains were from diverse geographical areas and hosts and included examples of the A-, B-, and non-B-biotypes. All recent collections were multi-resistant to these insecticides which have been used extensively for their control. The patterns of cross-resistance for the OPs were clear but less so for the pyrethroids. All populations that resisted profenofos and cypermethrin also resisted the combination of profenofos and cypermethrin. Although the importance of selection pressure on levels of resistance was not easily quantifiable the highly selected populations exhibited the highest levels of resistance. The significant within, as well as between, biotype variation in resistance factors clearly indicated that insecticide resistance and biotype were not directly related. The roles of acetylcholinesterase sensitivity and general esterase activity in resistance to OPs and pyrethroids are discussed.

The development and reproduction of 60 clones of Sitobion avenae (Fabricius), collected in the Rennes Basin, were compared on a resistant Triticum monococcum (Linnaeus) line (Tm44) and a susceptible Triticum aestivum (Linnaeus) cultivar (Arminda). All clones had lower larval survival and mean fecundity when reared on Tm44 in comparison with Arminda. They all performed equally well on Arminda whereas there was a marked and continuously distributed variation in performance parameters among clones maintained on Tm44. The plant species, from which clones originated, significantly affected aphid performances on resistant Tm44. A more detailed experiment was carried out with four clones, shown to differ in their level of fitness on Tm44. Their performances were compared on resistant (Tm44 and Tm46) and susceptible (Tm47 and Arminda) wheat genotypes. On the basis of larval development time and intrinsic rate of natural increase (rm), two types of response were distinguished among the four clones: clones Sa1 and Sa39 appeared to be less affected by Tm44 and Tm46 resistance than Sar2 and Sa48. Moreover, Tm46 was much less resistant to clone Sal than was Tm44. These results are discussed in relation to the origins of the variation in performance of S. avenae on resistant wheat, and their implications in plant breeding for resistance to S. avenae.

Population phenologies of the whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), in young cassava crops in Côte d'Ivoire, West Africa, are described for three field seasons. Populations of all stages were consistently greatest 6–12 weeks after the crop was planted. The number of adults on plants as well as on attractive and non-attractive sticky traps displayed cycles of buildup and decline each year, the periodicity of these cycles corresponding to the generation time of B. tabaci under field conditions. Adult population declines were probably caused by emigration from the crop. Rainfall was negatively correlated with both nymph and adult populations, possibly due to reduced oviposition after rain. B. tabaci is the vector of African cassava mosaic geminiviruses (ACMV) and the observed B. tabaci population trends fit well with the pattern of ACMV buildup in the crop.

A gall midge recently found on Dendrobium orchids in Florida, USA, is identified as Contarinia maculipennis Felt. The identification is based on anatomical similarity to a polyphagous species originally described from Hawaii but which now appears to be from south-east Asia. Contarinia maculipennis is redescribed and compared to Contarinia solani (Rübsaamen) and C. lycopersici Felt, two species with which it has been confused in the literature.

In Zimbabwe, catches of Glossina morsitans morsitans Westwood and G. pallidipes Austen, at an odour source produced by up to 60 tonnes of cattle, fell by 90% from April to October 1987. With the time effect removed, the catches were: positively correlated with daily maximum temperature; up to twice as high with a trap as with an electrified target; and unaffected by the presence of an incomplete ring of electrified netting (11.5 m diameter) around the catching site. Catches increased as a power of bait mass in accord with the theory of odour dispersal. The power was ca. 0.32–0.44 for G. pallidipes, ca. 0.15 for post-teneral G. m. morsitans, 0.67 for Stomoxyinae and 0.48 for non-biting muscids. Earlier results from dose-response studies accord with the new model. Tsetse catches were 1.7–4.5 times higher with 20 tonnes of cattle as bait than with a synthetic simulate of this dose, consisting of carbon dioxide, acetone, butanone, octenol and phenolic residues. Important olfactory components thus remain to be identified. Trap efficiency for G. m. morsitans rose from 10–20% to 40% with increasing bait mass between 0 and 5 tonnes; thereafter bait mass had no effect. Increased efficiencies were also seen in Stomoxyinae (5 to 60%;) and in post-teneral G. pallidipes (45 to 70–80%). Increases in catch for bait mass greater than five tonnes were due to increased attraction rather than increased efficiency. Targets were 60–66% efficient for G. pallidipes, regardless of dose; for G. m. morsitans the efficiency was ca. 54% when unbajted and 24–35% when 60 tonnes of cattle were used as bait. The probability that G. pallidipes landed on the cloth part of the target, rather than colliding with the flanking nets, increased as the square of the bait mass for both sexes—from 0.11 to 0.22 for males and from 0.06 to 0.15 for females. There was no effect of bait mass on landing probability for G. m. morsitans and no difference between the sexes; ca. 11% of the catch landed on the cloth portion of the target. Efficiency and landing behaviour were independent of climate and season.

Pyrethroid-impregnated bednets are being used nationwide in The Gambia. The future success of this malaria control programme depends partly on the vectors remaining susceptible to those insecticides used for treating the nets. The present study was carried out on the south bank of the river Gambia, during the first large scale trial of nets in this country. Thus this area represents a sentinel site for detecting insecticide resistance in local vectors. This study gives an example of how a system of early detection for resistance problems can be set up in a relatively complex situation where multiple vectors and non-vectors are present. Samples of the Anopheles gambiae complex were caught indoors using light traps in twelve villages used in the bednet study. In all villages A. gambiae sensu stricto Giles was the predominant member of the complex as determined using the rDNA-PCR diagnostic assay. Limited bioassays with DDT and permethrin, and biochemical assays for a range of insecticide resistance mechanisms suggest that the A. gambiae complex remains completely susceptible to all major classes of commonly used insecticides including pyrethroids. Biochemical assays suggest that a low frequency of DDT resistance may occur in A. melas Theobald. This is based on elevated glutathione S-transferase levels coupled with increased levels of DDT metabolism and does not involve cross-resistance to pyrethroids. Therefore we do not envisage a decline in the efficacy of treated nets against malaria vectors in the study area in the immediate future, although monitoring should be continued whilst wide-scale use of impregnated bednets is operational.

The spatial distribution of the parasitic mite Hemisarcoptes coccophagus Meyer on two armoured scale insects (Homoptera: Diaspididae) was highly aggregated in the field. Mites were more aggregated on young than on ovipositing host scale females. No differences in the mite's distribution pattern were found between latania scale (Hemiberlesia lataniae (Signoret)) and oleander scale (Aspidiotus nerii (Bouché)). Mite aggregation was density-dependent on ovipositing host females (the degree of overdispersion decreased as mite abundance increased), but density-independent on young females. The effect of density-dependent and independent mite aggregation on the proportion of hosts escaping attack at different parasite abundances was simulated, and its relevance to biological control of Diaspididae is discussed.

Tsetse populations and trypanosome prevalence in cattle were monitored from 1986 to 1993 in the Ghibe valley, south-west Ethiopia. From January 1991 to December 1993 between 2000 and 4000 cattle were treated at monthly intervals with a synthetic pyrethroid insecticide, cypermethrin (RS-alpha-cyano-3-phenoxy- benzyl [1RS]-cis, trans -3-[2,2-dichlorovinyl]-2,2-dimethylcyclopropane carboxylate). An approximate dosage of 1 ml per 10 kg bodyweight was used to control tsetse flies (Glossina spp.). Treatments were given as ‘pour-on’ applications along the backlines of animals, using automatic drench-gun applicators. This resulted in a decline of 93% in the apparent density of G. pallidipes Austen. A reduction of 83% in the apparent density of G. morsitans submorsitans Newstead was also observed. This reduction was associated with a reduction in trypanosome prevalence in cattle of over 74% in 1993, despite a high level of resistance to all available trypanocidal drugs. The numbers of Stomoxys spp. (Diptera: Muscidae) and Tabanidae were also significantly reduced (P < 0.01).

Trioza vitreoradiata (Maskell), a native of New Zealand, has recently been noted feeding on Pittosporum spp. (Pittosporaceae) in south-western Britain, where it causes damage to windbreaks and nursery plants. Its economic impact and nomenclatural history are discussed, and modifications to published keys to adults and nymphs of British Psylloidea are suggested to enable its recognition.

The bruchid Bruchidius atrolineatus (Pic) causes significant damage to the stored protein rich seeds of cowpea, Vigna unguiculata, in the West African Sahel. Twenty varieties of cowpea were evaluated for susceptibility to attack by B. atrolineatus in the laboratory. The bruchid showed differential response to the seeds in terms of developmental period, percentage adult emergence, seed weight loss due to feeding by one larva, adult weight at emergence and life-time fecundity of females reared from them. Based on these criteria, IT85F-2205 and IT84S-275-9 were the least susceptible varieties. The development of B. atrolineatus was most significantly delayed in these varieties. The beetle larvae consumed less of their seed material and adults reared from them were smallest and least fecund. The varieties IT87S-1393, IT90K-391 and IT84D-460 also had relatively lower susceptibility to the beetle than others. In a no-choice oviposition experiment, B. atrolineatus females laid equally on all varieties. Percentage egg hatch on the different cowpea varieties did not differ significantly. The results are discussed in relation to previous reports on susceptibility of cowpea and other legumes to bruchids.

DDT-resistant Anopheles gambiae Giles from Zanzibar, Tanzania, had increased levels of DDT-dehydrochlorination compared to a DDT-susceptible strain. Glutathione S-transferases (GSTs) are responsible for conversion of DDT to DDE in both the susceptible and resistant strains. Sequential column chromatography, including Q-Sepharose, S-hexylglutathione agarose, hydroxylapatite and phenyl Sepharose, allowed the partial purification of seven GSTs. All seven GSTs possessed different degrees of DDTase activity. There was an eight-fold increase in total DDTase activity in the resistant compared to the susceptible enzymes. Characterization with three substrates, 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB) and DDT, revealed the different substrate specificity for each isolated GST indicating different isoenzymes. GST Va possessed 60% of total DDTase activity suggesting that it contributed most to DDT-metabolism in this insect species. The DDTase activity of the GSTs in both strains of A. gambiae were found to be correlated with the GST activities toward DCNB. Preliminary studies on DDT-resistant and susceptible A. gambiae showed that both DDT-resistance and the increased levels of GST activity were stage specific which suggested that different GSTs may be involved in DDT-resistance in adults and larvae of A. gambiae.

Helopeltis pernicialis, a new species of bryocorine Miridae, is described from northern Australia, where it has become established as a serious pest of cultivated cashews, Anacardium occidentale (Anacardiaceae). Information on the biology and pest status of the bug is provided from studies conducted near Darwin, Northern Territory.

The influence of green ants, Oecophylla smaragdina (Fabricius), on insect pests of cashew, Anacardium occidentale Linnaeus, in tropical northern Australia was investigated using field surveys and field observations. Oecophylla smaragdina was abundant in the native vegetation of the area, and it was a dominant predator when found in cashew plantations. Oecophylla smaragdina significantly reduced the numbers of the four most important species of insect pests (Helopeltis pernicialis Stonedahl, Malipatil & Houston, Penicillaria jocosatrix (Guenée), Amblypelta lutescens (Distant) and Anigraea ochrobasis Hampson) on cashew trees, and trees with higher numbers of O. smaragdina produced higher quality nuts than trees with fewer numbers of O. smaragdina. Other ant species also reduced pest numbers, but not as much as O. smaragdina. The possibility of using O. smaragdina to control insect pests of cashew in the future is discussed.

Shortly after its invasion into Europe, the western flower thrips, Frankliniella occidentalis (Pergande), became a more severe pest of greenhouse crops than the onion thrips, Thrips tabaci Lindeman. To test whether this differential pest status was due to a larger capacity of population increase, a comparative life history study was carried out on cucumber (Cucumis sativus cv. Corona). Experiments at 25°C showed that the egg-to-egg period of F. occidentalis was shorter, but its peak ovipositional rate was lower and its offspring sex ratio more male biased. These differences resulted in a slightly lower intrinsic rate of population increase (rm) for F. occidentalis than for T. tabaci (0.166 vs. 0.176/day). It was shown experimentally that between 15 and 28°C, developmental rate of F. occidentalis is linearly related to temperature, with a theoretical threshold temperature similar to the value reported for T. tabaci (10.9 vs. 11.5°C). It is argued that the rm-value of F. occidentalis will not be higher than that of T. tabaci for any temperature within this range. Alternative explanations for the difference in pest status between the two thrips species are discussed.