The biology, damage and control of the sugarcane pest Pyrilla perpusilla Walker are reviewed. The present systematic position, distribution and the range of alternative host plants are surveyed and the life cycle and the extent of damage caused by the pest are considered in detail. The factors influencing the abundance of the insect are discussed, with emphasis on their use in reducing the population of the pest. Much of the published data in this area is based on un replicated observations. However, potential biological control agents for the insect are evaluated with special reference to the most effective nymphal and adult ‘parasitoid’, the moth Epiricania melanoleuca (Fletcher). Many other potential biological control agents have received some study, but in most cases, little more than basic biological information on phenology and life cycle has been published. As considerable changes in chemical control practices over the past fifty years have occurred, these, together with other control methods such as agronomic, mechanical, cultural and host plant resistance approaches are discussed along with prospects for the future, sustainable control of the pest. Research areas which are in need of more work are identified: these are biological control and cultural practices. It is suggested that an integrated approach to future research should be made, incorporating at least host-plant resistance and predation.

Many aphid species have life cycles which alternate between asexual reproduction during spring and summer and sexual reproduction in autumn. This paper describes the sequences of morphs produced by clones of Rhopalosiphum padi (Linnaeus) in response to a range of photoperiods and temperatures in the laboratory, and under semi-natural conditions at the time of year when the transition from parthenogenetic to sexual reproduction occurs. By using similarities in the order in which the various morphs were born, clones of R. padi were found to produce eight progeny sequence types. A clone of R. padi will produce these sequence types sequentially as it changes from parthenogenetic to fully sexual reproduction. The progeny sequence produced by clones under conditions corresponding to those of spring and summer consist of parthenogenetic females only. During late summer, production of parthenogenetic females is followed by males. Later in the year, a clone produces progeny sequences consisting of parthenogenetic females, gynoparae and males. The asexual phase of reproduction is terminated in late autumn when only gynoparae and males are born. A minority of clones terminate parthenogenetic reproduction by producing only gynoparae. The function of these changes in progeny sequence in maximizing the reproductive success of a clone of R. padi is discussed.

The foraging behaviour of frequency-dependent prey selection by larval instars of Toxorhynchites splendens (Wiedemann) was studied in the laboratory. Prey size selection (second vs fourth instars of Aedes aegypti Linnaeus or Anopheles stephensi Liston) by third and fourth instar predators was frequency-dependent. However, in the case of second instar predators, prey size selection was not frequency-dependent and the predator preferred second instar to fourth instar prey. When offered second instars of Aedes aegypti and Anopheles stephensi the preference for one species over the other was frequency-dependent in all the three predator instars. The role of frequency-dependent prey selection in the stability of prey—predator interaction at low equilibrium levels is discussed.

The diamondback moth, Plutella xylostellaLinnaeus (Yponomeutidae), remains one of the most serious pests of crucifers in many parts of the world, particularly in South East Asia. This paper reviews the wide array of strategies which have been used in attempts to control P. xylostella over the last 40 years and consolidates the fragmented and sometimes hard-to-access literature on two and three level trophic interactions (e.g. host plant—herbivore, herbivore—natural enemy and host plant-herbivore—natural enemy interactions) involving the pest. Special reference is made to studies and examples from South East Asia, and in particular Malaysia, where P. xylostella and its primary parasitoids have been well studied owing to the great economic significance of the pest in this region. It is suggested that a multitrophic approach to research may assist in the development of more sustainable methods for the management of P. xylostella and overcome some of the problems inherent with insecticide-intensive methods.

A commercially-available, hand-applied PVC resin formulation of the sex pheromone of the striped rice stem borer, Chilo suppressalis (Walker) was used to control the yellow stem borer, Scirpophaga incertulas (Walker), in a 20 ha mating disruption trial in West Bengal, India, in 1992. Indirect measures of mating disruption were used to compare the pheromone-treated plot with an untreated control plot and a farmers' practice plot where a conventional pesticide control regime was practised. The results showed that the level of ‘white head’ damage in the pheromone-treated plot was significantly lower than that recorded in other treatment plots and that the relative percentage of the larvae of the two major stem borer species, S. incertulas and Chilo polychrysa (Meyrick) found in the region changed from 88% S. incertulas in the farmers' practice plot to 65% in the pheromone-treated plot. The yields of grain and straw recorded in the pheromone-treated plot were significantly higher than in the untreated control plot but not significantly different from those recorded in the farmers' practice plot.

The parasitoids Microctonus hyperodae Loan and M. aethiopoides Loan have been introduced into New Zealand to control the forage pests Listronotus bonariensis (Kuschel) and Sitona discoideus Gyllenhal, respectively. Laboratory experiments were carried out to investigate the effect of host–parasitoid ratio, and exposure time on host survival, parasitism, oviposition and feeding. Cages of 20 field collected weevils were exposed to 0, 1, 3 or 6 parasitoids for 0, 1, 12 or 48 hours, maintained until parasitoid pupal emergence, and surviving weevils dissected. Over the ranges studied, increasing parasite number, and to a greater extent, period of exposure of parasitoids to their hosts increased parasitism levels. Microctonus aethiopoides achieved higher levels of parasitism in S. discoideus at the lower parasitoid contact treatments than did M. hyperodae in L. bonariensis. Fecundity in unparasitized weevils was progressively reduced in both L. bonariensis and S. discoideus in relation to increasing exposure to parasitoids. Feeding was reduced by about 40% in L. bonariensis for at least four days after parasitoids were removed, and in S. discoideus for the duration of the experiment, averaging 15%. Results were discussed in relation to possible mechanisms of indirect effects of parasitoids on unparasitized hosts.

Plant characteristics often influence the distribution of herbivores and natural enemies. In turn, the degree of their spatial association is likely to influence the ability of natural enemies to control pests. Also, an understanding of pest distribution patterns is important for the development of reliable and cost-effective sampling protocols. In this study, we assessed the effect of cotton variety and developmental stage on the within-plant distribution and degree of spatial overlap between populations of two thrips species and their predators. In the two studied varieties, cv. Pima and Acala, almost all Thrips tabaci Lindeman inhabited the leaves, while Frankliniella occidentalis (Pergande) colonized only the flowers. With respect to the predators, most Chrysoperla carnea (Stephens) were found on the leaves of both varieties, whereas predatory Orius spp. colonized mainly the flowering structures on Pima plants but the leaves on Acala. This variability in prey and predator distribution resulted in a significant and positive correlation between thrips and predator populations on Pima but not on Acala plants. The results also suggest that, overall, thrips are most likely to be preyed upon on squares and to be relatively safe in flowers. An intermediate but relatively high risk of predation apparently occurs on the leaves. The significance of these within-plant distribution patterns for the monitoring of thrips populations is discussed.

Gas chromatography analysis of Lutzomyia longipalpis (Lutz & Neiva) pupae and fourth instar larvae revealed a compound which was not present in other larval stages. Squashed pupae were repellent to conspecific larvae and ants (Lasius niger (Linnaeus) (Hymenoptera: Formicidae)), whereas second and third instars were not. Hexane extracts of pupae were repellent to conspecific larvae and L. niger, but extracts of second and third instars were not. The biologically active chemical was isolated from pupae and fourth instars and was found to be repellent to conspecific larvae and L. niger. The possibility that pupae and fourth instars may use a combined chemical and mechanical defensive strategy to avoid predation and cannibalism is discussed.

Mortality responses of adult New Zealand flower thrips, Thrips obscuratus (Crawford) to controlled atmospheres were assessed. Temperature (0–48°C) and time (1–24 h) had major effects on mortality. There were approximately two-fold increases in thrips mortality between atmospheres with 40 and 60% CO2, when there was 0 or 2% O2 present in treatments of 0°C for 4 h and 24 h; 12°C for all exposure times; 24°C for 1 h. Thrips mortality was significantly greater when there was no O2 in the test atmosphere, than when there was 0.25, 8 or 12 or 20% O2. The results show that there are a variety of ways produce infested with New Zealand flower thrips could be treated with controlled atmospheres to achieve high mortality. These data can be used as the basis of potential quarantine treatments depending on the produce being exported.

Helicoverpa armigera (Hübner) larvae were collected from field crops and wild hosts in India, Nepal and Pakistan from 1991 to 1995, and ninety eight laboratory cultures established. Cypermethrin, fenvalerate, endosulfan, quinalphos, monocrotophos and methomyl insecticides were topically applied to 30–40 mg, first laboratory generation larvae and resistance determined from log dose probit bioassays. Significant levels of cypermethrin and fenvalerate resistance were found in all field strains, demonstrating that resistance to at least some pyrethroids is now ubiquitous in H. armigera populations in the Indian subcontinent; cypermethrin and fenvalerate resistance levels ranged from 5– to 6500–fold and 16– to 3200–fold respectively. Pyrethroid resistance levels were highest in the intensive cotton and pulse growing regions of central and southern India where excessive application of insecticide is common. In all field strains assayed, pre-treatment with the metabolic synergist piperonyl butoxide (pbo), resulted in significant suppression of pyrethroid resistance. However, in nearly all cases, full suppression of resistance was not achieved. This residual non-pbo-suppressible resistance was most likely due to a nerve-insensitivity resistance mechanism. Pbo-insensitive resistance was highest in regions of India where insecticides were frequently applied to cotton and legume crops. In some regions where insecticides were heavily overused, a second high order nerve-insensitivity mechanism (possibly a Super -Kdr type mechanism), may have been present. Incipient endosulfan resistance (1–28-fold), was present throughout India, Nepal and Pakistan. Low to moderate levels of resistance (2–59–fold), were reported to the phosphorothionate group organophosphate, quinalphos, in India and Pakistan, but there was no evidence of significant resistance (0.4–3–fold), to the phosphate group organophosphate, monocrotophos, under our bioassay conditions between 1993 and 1994. H. armigera strains collected in Nepal in 1993 and 1994 were susceptible to quinalphos, but by 1995, 4–5–fold resistance was detected. It is probable that much of the resistance to pyrethroid, organophosphate and carbamate insecticides in the Indian subcontinent can be attributed to an inherited or inducible mixed function oxidase complex. Non-pbo-suppressible resistance becomes significant in regions and periods in the season when insecticide selection pressure on resistant H. armigera larvae on cotton and legume crops is very high.

The survival of Myzus persicae (Sulzer) clones, representing the full range of the recognized levels of insecticide resistance, was measured after 3–4 week exposure to the winter climate in the field. Ten separate trials were carried out using known numbers of first/second instar nymphs on unsprayed oilseed rape and groundsel. These predominantly showed a negative association between resistance level and the proportion of aphids recovered alive after exposure. The strength of the relationship correlated closely with three meteorological variables: the length of time that aphids spent below 2°C, mean rainfall and mean windspeed. We conclude that selection for resistance to insecticides is subject to counteracting selection by cold, wet and windy conditions in the UK winter. Revertant clones, that had spontaneously lost extreme resistance to insecticides despite retaining resistance genes, survived no better than aphids that had kept their high resistance, indicating that overproduction of esterase was not the reason for poor survival.

Adults from seven strains of Bemisia tabaci (Gennadius) were tested with nine insecticides or combinations in both leaf-dip bioassays and the Rothamsted field simulators. A statistical model was used to describe the survival of the insects in the field simulators and comparisons made to the resistance factors from leaf-dip assays. Strains of B. tabaci shown to be susceptible in bioassays were well controlled by field rates of the insecticides in the field simulators. For each insecticide or combination, the degree of adult survival in field simulators after insecticide treatment was positively related to the resistance factor. However, similar resistance factors for different insecticides gave quite different adult field simulator survival. In populations with high resistance factors, adult mortality in the field simulators after insecticide application was not different to untreated controls. These data provide information about the implications of B. tabaci resistance on the field performance of insecticides.

Several aspects of the biology of the tomato moth, Lacanobia oleracea (Linnaeus) were investigated when these insects were fed an artificial diet and kept under laboratory conditions. The six larval stadia occupied a total period of 35.6 days at 20°C and 65% r.h. Larvae of each stadium could be separated by their head capsule widths, but not weight ranges, which overlapped. Feeding studies carried out on larval L. oleracea revealed instar dependent changes in the indices of food consumption and utilization. Larvae increased in weight from the fourth to sixth instar due to a combination of the increased efficiency with which ingested food was converted to body tissue, and increased food consumption by older larvae. Sixth (final) instar larvae exhibited three distinct behavioural phases; during one of these, the feeding phase, larvae consumed a greater amount of diet than either the fourth or fifth instars. The mean pupal period of non-diapausing pupae was 25 days. Pupal diapause was induced when larvae were reared under short day conditions. The male to female sex ratio of adult moths was 1:1.3. Mating generally began during the first scotophase after adult eclosion, and stopped soon after the start of the next photophase. Females usually mated only once, but males were capable of mating at least seven times. Oviposition normally commenced on day 2 of adult life, and the mean total egg production was 1186 eggs/female. Sex pheromone components were not present in solvent extracts of the pheromone glands of 20-day-old female pupae, but low levels were detected in pharate adults. A further increase in pheromone levels in newly-emerged moths was detected and, in isolated virgin moths, pheromone levels increased each day of adult life until day 9. Pheromone levels were significantly lower in two-day-old mated adult females, than in two-day-old virgins.

Age composition of the filarial vector mosquito Culex quinquefasciatus (Say) was determined by examining the number of ovariolar dilatations of 1200 adult females from Calcutta. Average duration of the gonotrophic cycle was 4.5 days. The proportion parous, the daily survival rate and daily mortality rates of the natural population were 0.53, 0.87 and 13%, respectively. The oldest mosquito sampled in the study area passed eight gonotrophic cycles in its lifetime.

Single applications of slow-release pheromone formulations were used to control yellow stem borer, Scirpophaga incertulas Walker, by mating disruption in two trials on rice in India. The first trial compared the efficacy of two formulations containing 1:10:1 and 1:10:0 ratios of (Z)-9-hexadecenal, (Z)-ll-hexadecenal and (Z)-9-octadecenal, components of the S. incertulas pheromone, and a commercially-available formulation, Selibate CS, containing the related Chilo suppressalis Walker pheromone, a 1:10:1 blend of (Z)-9-hexadecenal, (Z)-ll-hexadecenal and (Z)-13-octadecenal, with farmers' practice plots treated with insecticides. Pheromone trap catches indicated that in each of the pheromone-treated plots the catches of male moths were reduced by up to 98% compared with catches in the insecticide-treated plots suggesting that pheromone-mediated communication was disrupted. Larval damage ranged from 5.7 to 8.1% white heads (WH) in the insecticide-treated plots compared to a significantly reduced range of 2.1 to 2.4% WH in the pheromone-treated plots. There was no significant difference between the damage estimates recorded for each of the different pheromone treatments. A second trial compared the effect on efficacy of applying the two-component pheromone formulation on different dates, 9–12 and 39–44 days after transplanting. Both pheromone treatments gave significantly lower levels of WH damage compared to equivalent insecticide treated plots; 1.8, 2.0, and 6% respectively. In both trials rice grain yields increased by between 5 and 12% in pheromone-treated plots compared to insecticide treated plots, which was due, at least in part, to the cumulative effect of reduced stem borer damage in both the tillering and reproductive stages of the crop cycle. The formulations exhibited pseudo-zero order release rates with field lives of between 70 and 90 days.

Only a few symbionts and mycetocytes in the bird cherry–oat aphid Rhopalosiphum padi (Linnaeus) reared for three days were affected on plants treated with 50 ppm benomyl. The symbionts of aphids reared for the same time on plants treated with 100 ppm benomyl, however, were abnormal and at an early stage of degeneration. Mycetocytes contained more residual bodies than normal. The symbionts and mycetocytes of embryonic aphids on such plants were also abnormal. When aphids were reared for 3 days on plants treated with 200 ppm benomyl, the symbionts and mycetocytes were drastically affected. Most of the symbionts were very abnormal and had degenerated. The mycetocytes were full of electron-lucent and electron-dense structures intermixed with abnormal cell organelles. Symbionts and mycetocytes of embryonic aphids were abnormal. In contrast, when the systemic insecticide pirimicarb was used to kill aphids, it did not affect the symbionts and mycetocytes. When aphids were reared for 6 days on plants treated with 50 ppm benomyl, their symbionts and mycetocytes and those of their offspring were also degenerate and abnormal, as were those of Fl generation aphids from mothers reared from birth on plants treated with 50 ppm benomyl. From a consideration of the known mode of action of benomyl on tubulin and the presence of tubulin only in the mycetocyte cells, it is concluded that the degeneration of symbionts in benomyl-treated aphids is a secondary consequence of the degeneration of the aphid mycetocytes.

Exposure of freshly laid eggs (<24 h old) of Earias vittella Fabricius (Lepidoptera: Noctuidae) and Dysdercus koenigii (Fabricius) (Hemiptera: Pyrrhocoridae) to volatiles from bulbs of Allium sativum significantly reduced their hatchability. Eggs of Spodoptera litura (Fabricius) (Noctuidae) treated likewise, failed to hatch. Eggs of Helicoverpa armigera (Hübner) (Noctuidae) were more tolerant and showed only a slight decrease in mortality. None of the immature stages of D. koenigii and H. armigera and only 30% of those of E. vittella that hatched from treated eggs managed to complete their metamorphosis. A few larvae of H. armigera developed to the pupal stage but their pupal weights were markedly low. These findings are interpreted as the chronic effects of volatiles affecting larvae/nymphs following developmental defects sustained during embryonic development. The known chief constituents such as allicin, 2-propene sulfenic acid, 2-propene thiol, propylene, thioacrolein and ajoene present in the volatiles were presumed to be responsible for the adverse consequences reported here.

Helicoverpa armigera (Hübner), H. assulta Guenée and Heliothis peltigera (Denis & Schiffermüller) were collected as mixed populations from safflower and the wild host Datura metel, from Patancheru, Andhra Pradesh, India, in 1992 and 1993, and their toxicological responses to insecticides determined. Both Helicoverpa armigera strains were highly resistant to cypermethrin, fenvalerate, endosulfan and quinalphos insecticides, based on resistance ratios relative to laboratory reared susceptible strains. There was no evidence of resistance development in H. assulta and Heliothis peltigera to the same chemicals. Light trap data collected from 1974 to 1987 showed that Helicoverpa armigera was at least 100 × more abundant than the other two species over most of the cropping season. Peak catches of H. assulta and Heliothis peltigera were confined to defined times in the season, corresponding with the flowering and fruiting periods of their respective host plants; August-October for Helicoverpa assulta and November-December for Heliothis peltigera. Helicoverpa armigera on the other hand, because of its high polyphagy on commercial and wild hosts, was abundant between August and April. Resistance has not developed in H. assulta and Heliothis peltigera in southern India, probably because of their restricted host range, limiting exposure to insecticides.