Control of yellow stem borer, Scirpophaga incertulas (Walker), in rice was attempted by mating disruption using the natural ratio of pheromone components, a 1:3 blend of (Z)-9- and (Z)-11-hexadecenal, in replicated trials at three locations in Andhra Pradesh, India, during the 1994 and 1995 dry seasons. The pheromone was formulated in SelibateR and applied by hand at a rate of 40 g a.i./ha. In Medchal and Nellore, pheromone-mediated communication was reduced by at least 94% for the first 50 and 64 days after application respectively, as measured by pheromone trap catch suppression. Compared with adjacent farmers' practice plots, subsequent dead heart and white head damage were reduced by 74 and 63% and 83 and 40% in Medchal and Nellore, respectively. In Medchal, average rice yields were increased compared to the farmers' practice plots, 4108 and 3835 kg/ha respectively, but in Nellore, they were the same as those obtained in the farmers' practice plots, 6400 and 6733 kg/ha respectively. In Warangal, the level of communication disruption over the first 70 nights after pheromone application was less than obtained in either Medchal or Nellore and averaged between 50 and 87%. The maximum dead heart and white head damage recorded in the pheromone-treated plots in Warangal were 2.8 and 15.7% respectively compared to 7.0 and 20.9% respectively in the farmers' practice plots. Differences in S. incertulas larval damage estimates obtained from the pheromone-treated and farmers' practice plots in Warangal were reflected in grain yields, 4036 and 3715 kg'ha respectively. Surveys of insecticide use indicated that 92% of smallholders in Medchal applied insecticide at least once per season while in Warangal over 60% applied insecticide on two or more occasions. The data show that season-long control of S. incertulas comparable to that obtained with conventional insecticides can be achieved by mating disruption in smallholder rice fields in India.

Tethered flight studies, carried out in southern Uganda with the leafhoppers Cicadulina storeyi China and C. mbila Naudé, showed that depending on species, the factors of age, gender, gravid status and rearing on virus infected maize had significant effects on flight, whereas host plant species and mated status appeared unimportant. Distributions of wing length (WL), body length (BL) and the parameters WL/BL and WL-BL were mostly uni-modal, but in two cases very weakly bi-modal. Regressions of log-transformed flight duration against these morphometric parameters were all non-significant, except for very weak (r2 = 0.01–0.04) relations with wing length. There was no conclusive evidence for the existence of separate short- and long-duration flight morphs among the leafhoppers. It is proposed that differences between our results and those of an earlier study of Zimbabwean Cicadulina populations, particularly in respect of the effects of gravid status on flight, and the existence of distinct flight morphs, are explicable in terms of the different seasonal and environmental constraints experienced by Ugandan and Zimbabwean populations. These favour long-range migratory flight at certain times of the year in Zimbabwe, but not in Uganda.

The well-established carboxylesterase-based resistance to insecticides in Myzus persicae Sulzer has recently been accentuated by the appearance of aphids with a modified acetylcholinesterase (MACE) insensitive to pirimicarb and the novel aphicide, triazamate. This target site resistance mechanism was found in M. persicae from crops in the UK for the first time in 1996, together with especially large proportions of aphids with R2 and R3 levels of carboxylesterases, a combination that was associated with serious insecticide failures. This paper describes the incidence of both mechanisms and discusses the implications for future recommendations for aphid control in the UK.

Flight traps and crevice traps for catching Prostephanus truncatus (Horn) and Sitophilus zeamais Motschulsky were studied in Kenya. The traps were baited with pheromones of these beetles, with or without synthetic maize volatiles. In the case of P. truncatus, which has a two component pheromone consisting of Trunc-call 1 (T1) and Trunc-call 2 (T2), the components were tested singly or in a 1:1 combination. The addition of synthetic maize volatiles to pheromone traps did not result in an increase in trap catch of either S. zeamais or P. truncatus. The pheromone of S. zeamais was an effective lure in both crevice and flight traps but the actual numbers captured were low. Captures with traps baited for P. truncatus were much greater. The response of P. truncatus to the two components of its pheromone was affected by the type of trap used. Crevice traps baited with either component alone caught fewer beetles than those baited with a mixture. In contrast, flight traps baited with T2 or the mixture were equally effective while traps with only T1 caught significantly fewer than either of these. These observations clarified apparent discrepancies between earlier studies in Tanzania and Mexico and are used to derive an hypothesis about the roles of T1 and T2; T2 appears to be a long-range attractant and T1 important for modifying the response to T2 to facilitate close-range orientation. Adult P. truncatus arriving at the traps were sexed, and in both flight and crevice traps the majority of captures were females even though in the experimental maize cribs the beetles were present in a roughly equal sex ratio. The role of the pheromone is discussed in the light of this observation.

Different Shin-Etsu twist-tie rope formulations, containing either the cotton bollworm, Helicoverpa armigera (Hübner) pheromone or pink bollworm, Pectinophora gossypiella (Saunders) pheromone, or both, in the same rope, were tested in Israel for mating disruption. The success of mating disruption was evaluated by the mating table technique, comparing the percentage of mating of virgin sentinel females in pheromone-treated and control plots. Two variants of this technique were evaluated, one with two mating tables per plot, each containing five to seven females, and the other with six to eight mating tables per plot, with only one female per table. The latter method was more sensitive than the former, particularly at low population densities. Two tests were conducted in 1995 in order to compare a blend of five components of H. armigera pheromone with a blend of two components for mating disruption. The application consisted of 2000 ropes/ha, each with 80 mg pheromone. Evaluation by the two mating table methods showed clearly that the formulation containing two components was superior to the five-component blend for mating disruption, suppressing mating almost completely for 49 days. A new combined formulation, HPROPE, containing 175 mg of the H. armigera two component blend and 65 mg of P. gossypiella pheromone was tested in 1996 for mating disruption of both pests. Application of 625 ropes/ha caused a high level of suppression of mating of H. armigera females for at least 94 days and that of P. gossypiella females for 161 days. The pheromone release rates were c. 625 mg/day/ha for H. armigera and 162 mg/day/ha for P. gossypiella. A ‘long-life’ formulation of P. gossypiella pheromone, PBW rope LR, applied at 125 ropes/ha releasing 137 mg/day/ha achieved complete suppression of mating over 75 days. This release rate of P. gossypiella pheromone was much lower than that currently used in Israel (275 mg/day/ha). The present study indicates that mating of females of two moth pests with different pheromones can be disrupted by one combined formulation.

Comparative studies were made on three presumed sibling species of the genus Eubazus, parasitoids of European Pissodes spp. weevils, to clarify their taxonomy and define diagnostic characters. Several populations of E. semirugosus (Nees), E. robustus (Ratzeburg) and Eubazus sp. were compared with respect to their morphology (mainly through morphometric analyses), fecundity, isoenzyme patterns and host preference. Crosses were made to assess the genetic and behavioural compatibility of the populations. In addition, the North American E. crassigaster (Provancher), a parasitoid of Pissodes strobi (Peck), was compared to E. semirugosus, a species selected for introduction against P. strobi in Canada. The ratio of the length of the ovipositor sheath to the fore wing length was the most discriminating morphometric variable, but discriminant analyses including several measurements were needed to completely separate European species. A canonical discriminant function provided a total separation between males of E. crassigaster and E. semirugosus, but not between females. Eubazus crassigaster and E. semirugosus were totally separated by the banding pattern of the enzyme phosphogluconate dehydrogenase whereas hexokinase and esterase provided a diagnostic separation between Eubazus sp. and E. robustus. Eubazus sp. differed from all the other species by having a greater number of ovarioles and, consequently, a higher potential fecundity. In a two-choice oviposition test, E. semirugosus and Eubazus sp. showed a significant preference for their natural host, P. castaneus De Geer and P. piceae (Illiger), respectively. A similar test made with their progenies reared under standard conditions showed that the difference in host preference was genetically fixed. Males and females of different species did not mate readily, in contrast to individuals from the same species. All attempts to interbreed E. robustus and Eubazus sp. failed, but a few crosses between E. semirugosus and the two other European species produced fertile offspring. These observations strongly suggest that the complex of Eubazus spp. parasitoids attacking Pissodes spp. in Europe is composed of at least three sibling species, two of which appear to have specialized on distinct host species that occupy exclusive microhabitats.

Life tables were developed to assess the significance of natural enemies on the dynamics of apple ermine moth, Yponomeuta malinellus Zeller, in southwestern Germany and to select parasitoid species for use in the biological control of this pest in Canada. During the study from 1993 to 1995 the abundance of Y. malinellus varied from 1.5 to 4.3 tents per 100 leaf clusters indicating that this was a non-outbreak population. From the life tables it was evident that the impact of egg predators accounted for 25–43% of the total generational mortality of Y. malinellus, more than any other known mortality factor. Percent parasitism varied from 18 to 30%, but the impact of parasitoids in relation to the total generational mortality of Y. malinellus from the life tables was remarkably constant at 11–14%. The loss of potential fecundity had an important influence on the generational mortality of Y. malinellus, but declined from 27% to 15% over the course of this study. This decline corresponded with a rise in the net rate of increase R0 from 1.35 in 1993 to 6.8 in 1995, despite the impact of insect predators and parasitoids on the generational mortality. Yponomeuta malinellus was attacked by five different obligate primary parasitoids, a single obligate hyperparasitoid, and three facultative hyperparasitoids. Of these, the oligophagous egg-larval parasitoid Ageniaspis fuscicollis Dalman (Encyrtidae) and the oligophagous larval-pupal and pupal parasitoid Herpestomus brunnicornis Gravenhorst (Ichneumonidae) were selected as potential biological control agents for Canada due to a minimal degree of interspecific competition.

In the absence of insecticide there may be intense selection against alleles conferring insecticide resistance, so that these alleles will decline in frequency. On the other hand, selection will act to favour alleles at modifier loci which cause resistance alleles to become coadapted and increase in fitness even in the absence of insecticide. The relative effectiveness of these two processes is of practical importance and theoretical interest. The fate of polymorphism for malathion resistance was studied in the saw-toothed grain beetle, Oryzaephilus surinamensis (Linnaeus). Five to six lines of each of four strains (8401, 8401sel, 8518B and L1040), each polymorphic for resistance phenotypes, were maintained in insecticide-free culture for up to nine generations, over which period the response of individuals to a discriminating dose of 65 mg m-2 malathion was determined. There was significant reversion to susceptibility in the related strains 8401, 8401se1 and 8518B. Assuming resistance to be primarily controlled by a single major locus, resistant homozygote and heterozygote fitnesses in the absence of insecticide were estimated to be 0.92, 0.83 and 0.68, respectively. The initial frequency of the resistant allele was inversely related to the time since last exposure to insecticide, and also to the fitness of the resistant allele. This could be explained by the selection of modifier alleles that reduce the fitness cost of resistance in the absence of insecticide. In strain L1040 the proportion of resistant individuals actually increased over time (after the second generation) in the absence of insecticide. The fitness of the susceptible allele in this case was 0.83. In all strains there was significant variation among lines in relative fitness and initial resistance allele frequency. Analysis of knockdown proportions revealed highly significant variation between generations that is not easily interpreted in genetic terms but is better explained by limitations of the knockdown bioassay.

Trajectory analysis was used to determine the direction and extent of windborne migrations of insects trapped in autumn and winter in south-east and east Asia for 12 years between 1968 and 1987. Nearly 2600 trajectories were drawn upwind at 10 m and 1.5 km from 15 catching sites and within the time (⋜60 h), wind speed (⋝5 km h-1) and temperature (⋝10°C) thresholds used, only 5% of the trajectories failed to locate a possible source and over 90% were completed in 40 h or less. The delphacids Nilaparvata lugens Stål and Sogatella furcifera (Horváth) dominated the trap catches (96%) with Cicadellidae (2.3%) and Diptera (0.5%) as the next most numerous. Very few Lepidoptera were reported (<0.3%). Nearly 80% of the trajectories were constructed in the prevailing Winter Monsoon and Trade winds, resulting in a southward displacement of insects towards putative overwintering areas as reported in previous studies. Tropical cyclones in autumn, produced trajectories which differed in both direction and extent from those in the prevailing winds, supporting the suggestion that the contraction of the distribution areas of rice pests at this time of year is the product of a series of movements in different directions. The results suggest that migrations continue throughout the year in the tropics and sub-tropics and indicate that this may be one way the capacity for long distance migration is maintained in some rice pest populations.

A strain of Cryptolestes ferrugineus (Stephens) bred for malathion-specific resistance was found to be 650 fold resistant at LD50 when compared with a susceptible strain bred from the same stock. Resistance was more than 98% synergized by triphenyl phosphate and S,S,S-tributyl phosphorotrithioate, but unaffected by piperonyl butoxide. AChE inhibition by malaoxon varied slightly between the strains. Non-specific esterase activity as measured by the hydrolysis of α-naphthyl acetate was slightly reduced in the resistant strain whereas there were no inter-strain differences in the hydrolysis of β-naphthyl acetate. Products of in vitro metabolism of malathion were identified by thin-layer chromatography and gas chromatography-mass spectrometry as α- and β-malathion mono-acids. It was therefore concluded that resistance was due to the hydrolytic breakdown of malathion by a malathion-specific carboxylesterase. The rate of in vitro malathion hydrolysis was found to be 31 times greater in the resistant strain. In vitro inhibition studies indicated that resistance is attributable to a carboxylesterase unique to the resistant strain. The implications of these results are discussed in relation to work recently carried out on malathion-specific resistance in dipterous species.

Pidorus euchromioides Walker has two separate diapauses during its life cycle, a winter diapause as a fourth larval instar and a summer diapause as a prepupa in a cocoon. Winter diapause was induced by short photoperiods. The critical day length of 13 h 20 min to 13 h 40 min at 23.3°C under insectary conditions was very similar to the critical day length (13 h 32 min) observed in the field. Sensitivity to day length was restricted to the first 9 days, corresponding to the first and second instars. The duration of larval diapause was not only strongly correlated with the inducing photoperiod, but also dependent on the number of short days experienced during the larval growth period. The shortest diapause occurred at the critical day length, or when the larvae were exposed for 6 days (a critical number of short days) to a photoperiod of LD 12 h:12 h. The summer diapause appeared to be primarily determined by a genetic factor and only occurred in part of the overwintering generation and the first generation. The two different diapause mechanisms play important roles. Winter diapause ensures that P. euchromioides synchronizes its development and activity with the phenology of specific host plants, and summer diapause provides the species with a high degree of adaptation to an unpredictable environment.

Whiteflies of the Bemisia tabaci (Gennadius) group are a major and increasing problem for agriculture throughout the world. In particular, the appearance and rapid spread of a highly virulent new form (silver-leaf whitefly, or B-biotype; Brown et ah, 1995), and recognition that the problem involves a complex of sibling species, host races and/or biotypes has stimulated intensive multidisciplinary research on this insect in recent years (Gerling & Mayer, 1996).