The Senegalese grasshopper, Oedaleus senegalensis (Krauss) (Orthoptera: Acrididae), is a major grasshopper pest of subsistence crops in the West African Sahel. In northern Mali, O. senegalensis spends the dry season in the egg stage in the soil and eclosion is triggered by the first rains which usually occur in May and June. Satellite imagery potentially enables rainfall, and hense O. senegalensis eclosion, to be monitored over much wider areas than those possible for ground-based observers. In 1990 and 1991, rain-gauge networks were set up at Mourdiah, northern Mali, and for each storm event, rainfall and Meteosat infra-red data were collected. The coldest convection clouds (< -70°C) produced rain 93.1% (n = 15) of the time, whereas warmer cloud (>- 10°C) produced rain only once (n = 61). The relationship between minimum cloud temperature and log transformed rainfall data was negative and highly significant (P < 0.0005). The maximum rain-gauge separation for reliable point measurements of rainfall was 8 km. Simulated rainfall experiments showed that O. senegalensis eclosion is influenced both by soil type and by the quantity of water added to the soil. A grasshopper survey after the first rain in 1994 showed that 8 mm of rain was sufficient to cause eclosion 9 days later. The implications of these results for improved O. senegalensis control are discussed.

Between 1908 and 1959, the predatory coccinellid, Hyperaspis pantherina Fürsch, was released for the biological control of the ensign scale Orthezia insignis Browne in Hawaii, four African countries and Peru. Substantial control was reported after all the releases, although the outcome was disputed in Malawi. Other coccinellid species and predatory Diptera were released against Orthezia spp. in various programmes from 1952 to 1977. In most cases these agents failed to establish, and there were no reported effects on the target Orthezia spp. In 1993, H. pantherina was released in St Helena for the control of O. insignis on the endemic gumwood tree, Comm idendrum robustum (Compositae). Preparatory investigations for this release revealed that the taxonomy and biology of this biocontrol agent were poorly known. Hyperaspis pantherina is redescribed and shown to be the correct name for the species previously known incorrectly as H. jocosa (Mulsant). Hyperaspis laeta Gorham and H. levrati (Mulsant) are transferred to the genus Cyra Mulsant (comb. n.). Hyperaspis metator (Casey) (stat. rev.) is resurrected from synonymy with H. levrati auctt. Studies of the life history revealed that H. pantherina normally lays its eggs directly onto the adult female O. insignis and that the first two instars of the larvae are frequently passed inside the ovisac of the female host, after which the host itself is often consumed. The information on the biology and taxonomy of H. pantherina, together with details of culturing methods, should facilitate the further use of this agent for the classical biological control of O. insignis, a pantropical pest.

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.

Lutzomyia verrucarum (Townsend) is an abundant anthropophilic phlebotomine sandfly in the Peruvian Andes between 1500 m and 3000 m asl, where it has been incriminated as a vector of both Leishmania peruviana (cutaneous leishmaniasis) and Bartonella bacilliformis (bartonellosis). Previous studies of this vector demonstrated that sandfly activity, measured by sticky traps, was related to crop type. In this paper, we report the results of a field experiment in Peru (Department of Ancash) which show that a single human host in a crop does not attract Lu. verrucarum from distances of 5 m or more, and that there is a positive correlation between the number of Lu. verrucarum collected by sticky traps and the number attracted to a human host in the same field. The results imply that variation in sandfly activity between crop types could lead to differential risk of both leishmaniasis and bartonellosis for humans working at night in different crops.

A series of trials examining the feasibility of an attracticide technique for control of Spodoptera littoralis (Boisduval) are described. The technique combined the sex pheromone of S. littoralis with pyrethroid insecticide, λ-cyhalothrin, in 500 point-sources/ha at low rates of application of both components. It was envisaged that male moths would be attracted to contact the sources and subsequently suffer lethal or sub-lethal effects which would prevent mating. The pheromone was applied either as a sprayable microencapsulated (MC) formulation or in polyvinyl-chloride lures; emulsifiable concentrate and MC formulations of the insecticide were employed. Treatments were assessed by monitoring pheromone trap catches, mating of tethered females and, in one trial, numbers of eggmasses found in experimental areas. Mating levels and trap-catch in treatment plots were siginificantly reduced, compared to controls, for periods up to 5 and 24 nights after treatment, respectively. However despite a continuous period of mating suppression, achieved by repeated applications, no treatment-related reduction in egg-masses was observed. Two trials compared attracticide with mating-disruption treatments in which the insecticide was omitted. Similar levels of mating and trap-catch suppression were observed in the two treatments. It was concluded that the mating suppression observed in attracticide plots was due principally to disruption of chemical communication between the sexes, not to male mortality arising from contact with the insecticide sources. None of the attracticide treatments represented a viable control technique. Other practical and theoretical considerations arising from the results are discussed.

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.

Cyclodiene insecticide resistance persists in field populations of Drosophila spp. at a frequency of approximately 1% (0.01), despite the withdrawal of most cyclodiene type insecticides except endosulfan. However, we have previously documented that resistance-associated amino acid replacements in the gene Rdl, a γ-aminobutyric acid receptor, can significantly affect several channel functions of the integral chloride ionophore. We were therefore interested in investigating if different resistance-associated replacements confer significant fitness disadvantages and whether the use of endosulfan could be maintaining selection for cyclodiene resistance in the field. Using PCR amplification of specific alleles (PASA) within 3000 individual flies, we report that neither the alanine302 > serine (allele 1) replacement in Drosophila melanogaster Meigen nor the alanine302 > serine (allele 1) or alanine302 > glycine (allele 2) replacements in D. simulans Sturtevant showed any reduction in frequency in cage experiments run for one year in the laboratory in the absence of selection. Further, repeated applications of endosulfan selected significantly for cyclodiene resistance in the field. Thus the apparent absence of fitness cost, combined with the continued use of endosulfan, may maintain cyclodiene resistance at this relatively high frequency in field populations.

Helicoverpa armigera (Hübner) and H. punctigera (Wallengren) are major pests of cotton in Australia. The density of eggs and larvae of these species are sampled regularly throughout the growing season to assess the need for insecticidal control. A sampling system now widely used is based on binomial sampling combined with a series of conversion relationships developed as part of the SIRATAC computer based pest management system established in the early 1980s. A three year study was initiated to reassess the binomial sampling conversion relationship in the light of changed agronomic practices and new cotton varieties. New relationships were established to predict the mean number of Helicoverpa spp. present, based upon the number of infested plants found within a sample. Relationships are reported for the sampling of whole plants and the sampling of the terminal (top 20 cm) portion of cotton plants only. These new relationships will be incorporated into entomoLOGIC, a personal computer based pest management system now released to replace SIRATAC.

Gravid females of Lucilia cuprina (Wiedeman) in a laboratory cage orientated positively to samples of fleece. Newly-wetted fleece was significantly more attractive than dry fleece, an effect resulting from the action of water on the fleece and not just addition of water vapour to the volatile fleece kairomones. Fleece contaminated with serous exudate, resulting from myiasis by L. cuprina, was much more attractive than wet, uncontaminated fleece from the same sheep. Kairomones from wetted fleece consistently augmented the attractive effects of 2-mercaptoethanol and indole in separate experiments, and of hydrogen sulphide (released from saturated aqueous sodium sulphide solution) in one trial out of three, but not overall. It is suggested that volatile fleece kairomones play a part in eliciting orientation to sheep by gravid L. cuprina. Fleece kairomones may augment the efficacy of kairomones released by putrefactive conditions in the fleece, which are known to predispose sheep to fly strike. They may also provide an input which helps to retain L. cuprina populations in the sheep’s peridomestic precinct.

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 effectiveness of a sex pheromone trap designed specifically to deliver conidia (infective fungal propagules) of the entomopathogenic fungus Zoophthora radicans Brefeld (Zygomycetes: Entomophthorales) to male Plutella xylostella (Linnaeus) was investigated. In field experiments in the Cameron Highlands of Malaysia, synthetic pheromone lures attracted adult males P. xylostella at all times of the day whereas lures of virgin female moths attracted males only between the hours of dusk and dawn, when females are known to produce their pheromone. Adult male moths attracted to traps baited with synthetic pheromone spent a geometric mean time of 88 seconds within the inoculation chamber, a time compatible with the period adults must spend within a shower of Z. radicans conidia produced by uniform mycelial mats in order to become infected. The field longevity of male and female P. xylostella adults was found to be similar, with individuals living for a mean time of 4.9 days. This was sufficient time for male moths to respond to the pheromone, enter the trap, become infected with Z. radicans and succumb to that infection in the field (3–3.5 days) thereby releasing infective conidia into the cabbage crop.

Outbreaks of the African armyworm, Spodoptera exempta (Walker), in East Africa follow a seasonal pattern related to the movement of the inter-tropical convergence zone. The season typically begins in central Tanzania with primary outbreaks that coincide with the arrival of the rains. An analysis of 27 years' light trap records shows a high negative correlation between the total number of moths caught by light traps during the season over the whole country and the number of rain days during November in central Tanzania. Out of the 27 seasons, 22 could have been correctly predicted as ‘light’ or ‘severe’, using the November rainfall at one station, Dodoma, in time to give two months' warning before the peak of the season.

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.

The association of esterase (EST) activity with resistance to the organophosphorus (OP) insecticide methidathion was investigated in field-collected populations of whitefly (Bemisia tabaci (Gennadius)) in Israel. The inheritance of EST activity was studied by controlled crosses in the laboratory. Among-family variance of EST activity was highly significant although all families were maintained in the same rearing room. This indicates that genetic or common environmental effects due to rearing each family on a different caged plant must have been important. Heritability estimated from son-mother regression was h2=0.98, but this estimate seems to be unrealistically high. Daughter-mother and daughter-mid-parent regressions produced lower heritability estimates (as expected). None of the regression coefficients of daughters on mother, however, were significantly different from zero and the regression on parent explained only very small amounts of the activity variation in the offspring. Estimates obtained from intraclass correlations among offspring were higher and outside the acceptable range, reflecting the variance component due to the common environment. The predictive value of the heritability estimates appears to be very low. The frequency distribution of activity among individuals sampled from one insecticide treated site (AM) was skewed to the right, as previously reported. But samples from another site (TZ) showed a symmetrical distribution, unlike the previous pattern. When field collected individuals from AM were released on clean plants in the laboratory, samples taken from the plants one or more days later showed symmetrical EST distribution. Electro-phoretic paterns of field and laboratory samples were the same, but band intensity was stronger in samples from laboratory populations. Differences in mean EST activity between populations and sampling years were unrelated to methidathion resistance.

A method for physiological age determination in blackflies is described from studies on Simulium equinum (Linnaeus), S. ornatum Meigen, S. erythrocephalum (De Geer), and S. nigrum (Meigen) in Russia, and S. vittatum (Zetterstedt), and S.verecundum-venustum supercomplex in Canada. The method uses neutral red to stain the ovariolar structures which indicate preceding gonotrophic cycles. Two different processes can occur in the ovariole during the gonotrophic cycle: egg development with ovulation, or degeneration of a terminal follicle. Egg-sacs are resorbed and form zones of granulation which accumulate in the ovariole at each gonotrophic cycle. Following degeneration of the terminal follicle, a follicular relic (═gonotrophic dilatation) forms. The sum of zones of granulation plus follicular relics in each ovariole can indicate the number of completed gonotrophic cycles. However the number of follicular relics alone does not correspond to the number of preceding gonotrophic cycles and cannot reliably be used for determination of the parity of a female. Female flies collected in nature were categorized as: nulliparous; 1-parous; or multiparous. In multiparous females, most ovarioles have no more than two zones of granulation or a combination consisting of one zone of granulation and a follicular relic. Females in this category are considered to be 2-parous. In some ovarioles of parous females the germarium and terminal follicles were found to have disappeared.

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.

Seven presumed Mendelian enzyme loci (Est-2, Est-3, Gpi, Idh-l, Idh-2, Mdh-2 and Mpi) were characterized and tested for polymorphism in coffee berry borers, Hypothenemus hampei (Ferrari), sampled in Côte d′Ivoire, Mexico and New Caledonia. The average genetic diversity was H = 0.080. Two loci, Mdh-2 and Mpi were polymorphic, and thus usable as genetic markers. The population structure of H. hampei was analysed using Weir & Cockerham's estimators of Wright's F-statistics. A high degree of inbreeding (f = 0.298) characterized the elementary geographic sampling unit, the coffee field. The estimate of gene flow between fields within a country was Nm = 10.6 and that between countries was Nm = 2. The population genetic structure in H. hampei could be related to its known population biological features and history.

Use of the insect growth regulator (IGR) pyriproxyfen (Nemesis®) for the control of red scale Aonidiella aurantii (Maskell) (Homoptera: Diaspididae) on citrus in southern Africa has led to extensive disruption of the biocontrol of cottony cushion scale Icerya purchasi Maskell (Homoptera: Margarodidae) provided by the coccinellids Rodolia cardinalis (Mulsant) and other indigenous Rodolia spp. Similar effects on field populations of Chilocorus nigrita (Fabricius), a coccinellids predator of A. aurantii, have also been observed. The adverse effects of field-weathered residues of IGRs on the fecundity and egg viability of the coccinellids C. nigrita and Cryptolaemus montrouzieri Mulsant were determined in a laboratory bioassay. Residues of pyriproxyfen, a juvenile hormone analogue, and two chitin synthesis inhibitors, buprofezin (Applaud®) and triflumuron (Alsystin®), were tested. Exposure to residue-bearing leaves did not affect the number of eggs laid by Chilocorusnigrita, but a complete, or near complete failure of eggs to hatch ensured when adults were exposed to either 3, 7 or 19 week old weathered residues from a single application of pyriproxyfen or triflumuron. Three week old residues of buprofezin had the same effect, but both 7 and 19 week old residues no longer significantly reduced egg viability. Adults of both C. nigrita and Cryptolaemus montrouzieri commenced laying viable eggs within 20 days of being separated from all residue-bearing leaves. One week old residues of pyriproxyfen and triflumuron both significantly reduced progeny production by C. montrouzieri. Ten week old triflumuron residues were still detrimental to this species but pyriproxyfen residues of the same age were not. It was concluded that IGRs are not compatible with integrated pest management (IPM) for citrus in southern Africa, where coccinellid biocontrol agents play an important role.