Cotesia flavipes Cameron has been released several times in Africa for biological control of gramineous stem borers. Establishment has been reported on the Indian Ocean islands of Mauritius, Réunion and Madagascar, however, several attempts to introduce C. flavipes into continental Africa are reported to have failed. Recently, several cocoon masses of C. flavipes were recovered from south-western Kenya where the parasitoid was never released. Identifications of the parasitoids from south-western Kenya were based on morphological characters, allozyme frequencies, and mating experiments with laboratory populations of C. flavipes. It is hypothesized that C. flavipes became established from individuals escaping from a laboratory colony maintained in south-western Kenya in 1991.

RNA interference (RNAi) induced through double-stranded RNA (dsRNA) has been used widely to study gene function in insects. In this paper we demonstrate the efficacy of RNAi in the cotton bollworm, Helicoverpa armigera. Using CYP6B6 as the target gene, which is expressed in the fat baby and midgut of the lepidopteran pest H. armigera, we constructed the vector which expressed dsRNA of CYP6B6. Northern blot analysis showed that dsRNA expressed in the Escherichia coli (HT115) was target gene. The results also showed that the gene expression level and protein expression level of H. armigera larvae fed with dsRNA expressed by E. coli were significantly lower than those of all controls, but the gene expression level was more obvious than that at the protein level; significant lethality differences were also found between HT115 bacteria containing L4440-dsC1 treatment and HT115 bacteria containing L4440 vector or CK (ddH2O) in instar larvae on 4 day when continuous feeding, 32.45% mortality was recorded in the group of feeding HT115 bacteria containing L4440-dsC1 on 10 day. Our results suggest that the RNAi pathway can be exploited to control insect pests.

The effect of vine phenological stage during larval feeding on the reproductive output of Lobesia botrana (Denis & Schiffermüller) adults was assessed. Larvae were reared under field conditions on vine inflorescences, unripe or ripe berries simulating the first, second and third insect generations respectively. The resulting adults showed significant differences in body weight, longevity and reproductive output as measured by oviposition period, total fecundity and reproductive efficiency (viable eggs/body weight) for females, and spermatophore number and volume of the first spermatophore for males. Viable egg number was positively correlated with female body weight for all treatments but male reproductive efficiency (spermatophores/body weight) was not. The reproductive output of females from larvae reared on a standard semisynthetic diet was comparable to that of females reared on ripe berries whereas males showed a higher reproductive output when reared on semisynthetic diet. These results clearly show that data obtained from insects reared on artificial diet cannot be extrapolated to ‘field-derived’ adults. The results suggest that the variation in L. botrana reproductive output due to the larval food source should be taken into account as a potential factor affecting insect population dynamics. It is suggested that different intervention thresholds, such as those based on pheromone catches, may be needed for each of the three moth generations, to compensate for the increased fecundity and potential to cause larger amounts of crop damage of later generations.

The role of visual factors in the attractiveness of bodies to adult A. aegypti was investigated by exposing deer-mice in transparent or opaque, airtight or perforated, plastic containers. The visual factors proved to be roughly equivalent to the airborne emanations in attractiveness, being slightly the more attractive when the mice were normally moving, and the less attractive of the two when the mice were motionless.

The attractiveness of a moving black object was found to be nearly twice that of a stationary one. A deer-mouse immobilised by anaesthesia was roughly one-half as attractive as a normally moving one.

Mirroring surfaces are significantly more attractive than dull ones; a black enamel surface was more attractive than a flat black surface, and a silvered mirror more attractive than a polished metal surface. It was found that enhancement of the attractiveness of a black surface could be obtained by the movement of lines of shadow, not of points of light, across it.

Parasitoids employ different types of host-related volatile signals for foraging and host-location. Host-related volatile signals can be plant-based, originate from the herbivore host or produced from an interaction between herbivores and their plant host. In order to investigate potential sex- and species-related differences in the antennal response of parasitoids to different host-related volatiles, we compared the electroantennogram (EAG) responses of both sexes of the specialist parasitoid, Microplitis croceipes (Cresson), and the generalist, Cotesia marginiventris (Cresson), to varying doses of selected plant-based host-related volatiles: two green leaf volatiles (cis-3-hexenol and hexanal) and three inducible compounds (cis-3-hexenyl acetate, linalool, and (E,E)-α-farnesene). Mating had no significant effect on EAG response. Females of both species showed significantly greater EAG responses than conspecific males to green leaf volatiles, which are released immediately after initiation of herbivore feeding damage. In contrast, males showed greater responses than conspecific females to inducible compounds released much later after initial damage. Cotesia marginiventris females and males showed greater EAG responses than counterpart M. croceipes to the tested compounds at various doses, suggesting that the generalist parasitoid shows greater antennal sensitivity than the specialist to the tested host-plant volatiles. These results are discussed in relation to the possible roles of green leaf volatiles and inducible compounds in the ecology of female and male parasitoids.

Tomato yellow leaf curl virus (TYLCV) is the most frequently occurring virus in tomatoes in the Middle East, and the most harmful one. It is transmitted solely by the whitefly Bemisia tabaci (Gennadius). Within 4–6h of inoculative feeding, a whitefly can transmit TYLCV to a healthy plant with 80% probability. The symptoms are apparent after two to three weeks whereupon fruit-set is effectively terminated. The only means of controlling TYLCV is by controlling the whitefly. Until 1990 this was exclusively by insecticides. Starting in 1990, growers of greenhouse tomatoes in Israel began adopting insect exclusion screens to prevent inoculation of TYLCV. This article reports on the methods used in the search for efficient screening materials and presents data on their relative efficiencies in excluding B. tabaci and several other greenhouse pests. Ten materials were tested, of which five were found to be effective in excluding B. tabaciunder laboratory conditions. This number was reduced to three following field trials and trials in commercial tomato greenhouses. These materials are now in widespread use in Israel: by 2000 practically all table tomatoes in Israel were grown under exclusion screens. The use of exclusion screens has been shown to be an economically viable pest management method.

The facultative larval diapause of the khapra beetle, Trogoderma granarium Everts, is initiated extrinsically by temperature, crowding, and very low or very high humidity. In crowded populations, in tubes of wheat, the proportion of diapause larvae varies from very low (2 to 3 per cent.) in the upper part of the insect's temperature range to 100 per cent, in the lower part. Diapause larvae become more frequent with increasing population density, the frequency becoming noticeable at a density of about ten larvae per gramme of wheat (about 10 times their minimum food requirements). Accumulation of faecal pellets is a factor that induces diapause in crowded conditions. Many larvae that are kept singly enter diapause when fed on old culture food from which pellets have been removed: possibly in the old culture the pellets impart to the food a substance that initiates diapause. The availability of a suitable refuge, in which larvae can cluster, has no consistent effect on the proportion of diapause larvae. Factors that induce diapause also slightly increase the developmental period of non-diapause larvae.

In malted barley, more larvae enter diapause than in wheat, probably due to the intensification of crowding by the confinement of larvae to a few malt grains.

The relative importance of the factors that induce diapause is discussed. These factors help to explain observations in stores and conflicting results in the literature. The main function of diapause seems to be in assisting the larvae to survive periods of food shortage; diapause may also improve the survival of larvae in a cold winter and synchronise the emergence of adults. Of the factors inducing diapause, accumulation of faecal pellets precedes food shortage and falling temperatures precede the cold of winter, but the role of high and low humidities in this connection is difficult to assess. Diapause larvae play a major part in the dispersal of the species. The diapause of T. granarium is compared with that of other arthropods.

This study examines the spatial and seasonal patterning of mitochondrial DNA diversity in French populations of the bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus), on both its primary and secondary hosts. Our results confirm the presence of two major mitochondrial lineages that are generally associated with the breeding system variation (cyclic and obligate parthenogenesis) shown by this species. The strength of this relationship varies regionally, being most evident in the south and west. Cyclically parthenogenetic populations show no significant regional or seasonal genetic divergence reflecting high levels of gene flow, possibly promoted by their obligate host-alternation. However, obligately parthenogenetic populations show a north-south cline in the distribution of the dominant haplotypes. This pattern might result from a selective advantage of some obligately parthenogenetic lineages under cold temperature regime. Alternatively, this cline might be established by a gradient in the intensity of nuclear gene flow between cyclically and obligately parthenogenetic populations mediated by androcyclic males. The discrimination between these possible explanations will require extending analysis to include hypervariable nuclear markers.

Studies on Culicoides spp. biting midges in south-west Scotland in 1991 revealed that Culicoides impunctatus Goetghebuer, the dominant species throughout the season (May-September), was bivoltine, with a generation period of six weeks. Unseasonal climatic conditions during much of June resulted in a low proportion of first generation females surviving to the parous stage and a reduction in the overall, expected size of the second generation. Distinct behavioural phases of the female midges, such as resting, dispersal and host-seeking, were shown to be directly related to parity states (determined by fat body condition and ovarian development) during the gonotrophic cycle. Female flight activity increased after laying the first, autogenous egg batch, whereas males never flew far from the emergence site. The mean parous rate formula was used to calculate the survival rate of second generation nulliparous females, which was 0.57 per gonotrophic cycle.

The seven previously known species and one subspecies of Nephotettix are redefined, namely, N. virescens (Distant), N. nigropictus (Stål), N. cincticeps (Uhler), N. modulatus Melichar, N. malayanus Ishihara & Kawase, N. afer Ghauri and N. nigropictus yapicola Linnavuori. N. sympatricus is described as new. Nephotettix spp. fall into two groups, African (two species) and Asian (six species, one subspecies) which can be separated on genitalic characters. Distribution maps are given for each species. A key to the species based on external characters is given, but determinations should be confirmed by the genitalic characters.

Cuticular wax was extracted from adult females of Anopheles culicifacies Giles and analysed by gas liquid chromatography. The flies were taken from pure cage stocks of three sibling species: 56 individuals of species A, 43 of species B and 51 of species C. The three cytospecies were found to be significantly different in their cuticular hydrocarbon composition by a multivariate analysis of variance. Using discriminant analysis, each cytospecies was characterized by the amounts of C25-C33 hydrocarbons extracted from the cuticle, allowing criteria to be established for the identification of flies. By these criteria, specimens from stocks of known identity were allocated to the correct group with a high success rate. These results may reflect ecological differences among the sibling species.

Insecticide resistant Myzus persicae (Sulzer) employ increased esterase activity to detoxify insecticides by hydrolysis and sequestration. The amount of esterase, and hence resistance, in individual aphids can be determined by measuring either overall naphthyl acetate hydrolysis in crude homogenates, or the specific enzyme responsible (E4 or FE4) after electrophoresis or immunological isolation. The ability of a total esterase assay, done in microplates, to discriminate between susceptible (S) aphids and resistant variants (R1, R2) with different amounts of E4/FE4, was compared with the resolving power of the more elaborate immunoassay technique. The immunoassay gave the better discrimination between variants, resolving them all with greater than 95% confidence, with particularly good separation of R1, from S. The microplate assay using crude homogenates, although a poorer discriminator, identified most of the very resistant (R2) aphids, and provided a robust and widely accessible method for broadly representing the resistance of field populations.

Archeological records attest the early association of Sitophilus with stored cereals from the beginning of agriculture on Asia. The maize weevil (Sitophilus zeamais) became particularly damaging to maize, a cereal crop domesticated on Mesoamerica. We investigated the late evolutionary history of the maize weevil to gain insights on its origin, timing of association with maize, and genealogical relationship to the almost morphologically indistinguishable rice weevil (Sitophilus oryzae). Two mitochondrial genes (cytochrome oxidase subunit I and cytochrome oxidase subunit II) and the nuclear ribosomal gene region were partially sequenced. Analyses showed that the maize weevil shared no haplotypes with the rice weevil; instead, each species exhibited distinct mitogroups and ribogroups. The two weevil species likely split about 8.7 million years ago (95% highest posterior density: 4.0–15.0). Microsatellite data analyses sorted the 309 specimens from 15 populations of the maize weevil into three genotypic groups, which displayed low genetic differentiation and widespread occurrence worldwide. The maize weevil and the rice weevil are each a distinct species; both of which emerged prior to the onset of agriculture. The maize–maize weevil association took place after maize became widespread as a global crop. The maize weevil populations lack spatial genetic structure at the regional, continental, and intercontinental scales.

Cage experiments confirmed that, in the absence of natural enemies, populations of Aphis fabae Scop., attended on bean plants (Vicia faba) by the ant, Lasius niger (L.), multiply more rapidly than otherwise similar but ant-free populations. The average difference in numbers recorded, was about one-third, the maximum being 70 per cent. No doubling or trebling of aphid numbers as claimed by an earlier worker was ever recorded.

When the Aphids are attended by ants, their excretion behaviour alters and the normal dispersal of the apterae from the young apical growth of bean plants is considerably delayed.

No significant differences were found between the numbers of nymphs produced by individual Aphids from ant-visited and ant-free plants, respectively, living on leaves of the same age; but the numbers were significantly affected by the age of the leaf or part of the plant on which the Aphids had developed or were then feeding.

It is suggested that ant-attended aphid populations multiply more rapidly because most of the Aphids feed for a much longer time on young plant tissue where, presumably, their food supply is more nutritious.

Two strains of Helicoverpa armigera (Hübner), resistant to synthetic pyrethroids, were isolated from field populations collected in the irrigated cotton growing areas of northern New South Wales: an isofemale strain, Mfo, and a composite field strain, Field. A series of crosses were undertaken between the Mfo and susceptible strains to determine the genetic basis of the resistance. Dose-responses were obtained by bioassay using topical application of fenvalerate in acetone. Considerable variation in tolerance was observed in both resistant and susceptible strains. In the Mfo strain, the major shift in resistance phenotype (33-fold resistance) was due to a single major gene with incomplete dominance. The resistance phenotype was not diluted by 23 generations of backcrossing. The major resistance phenotype could be eliminated almost completely by the addition of piperonyl butoxide which affects oxidative breakdown of the pyrethroids by mixed function oxidase (mfo) enzymes. Similar results were observed in the Field strain. Monitoring for resistance in field populations will be imprecise because a true discriminating dose does not exist for susceptible and heterozygous resistant individuals.

In Zimbabwe, studies were made of the levels of known tsetse attractants present in natural ox odour. Typically an ox (400 kg) produced phenol (0.1 mg/h), 3-methylphenol (0.09 mg/h), 4-methylphenol (0.7 mg/h), 3-ethylphenol (0.01 mg/h), 4-ethylphenol (0.02 mg/h), 3- and 4-n-propylphenol (0.02 mg/h), l-octen-3-ol (0.01 mg/h), carbon dioxide (140 l/h), acetone (5 mg/h) and butanone (0.3 mg/h). Of these, only phenol, 4- and 3-methylphenol and carbon dioxide were always detected in ox odour. Studies were made of the numbers of Glossina pallidipes Austen and G. morsitans morsitans Westwood attracted to natural ox odour and synthetic odour, the latter consisting of blends of identified attractants dispensed at the doses naturally present in ox odour. Natural ox odour caught twice (P < 0.05) as many G. pallidipes and 1.5 (P < 0.05) times as many G. m. morsitans as the synthetic blend suggesting the presence of an unidentified attractant in ox odour. Passing ox odour through filters indicated that all attractants can be trapped on a combination of charcoal and sodalime filters but the unidentified attractant(s) may pass through a sodalime filter, and break through a charcoal filter used for more than 6 h. Increasing the dose of ketones in the synthetic odour from 2 to 100 mg/h doubled the catches at the source. Increases in ketone levels in hosts, induced by starvation or possibly trypanosomiasis, may increase attraction of tsetse to such animals.

Laboratory experiments examined interspecific interactions between larvae of three coccinellid species, Curinus coeruleus Mulsant (Chilocorinae), Harmonia axyridis Pallas and Olla v-nigrum (Mulsant) (Coccinellinae), and between these and larvae of the green lacewing, Chrysoperla rufilabris (Burmeister). Larvae of C. coeruleus, although defended on their dorsal surface with long spines, had the smallest mandibles, were the slowest-moving, and the least successful in interspecific larval combat. The long spines of third instar C. coeruleusappeared to reduce their palatability as food to H. axyridis and O. v-nigrum larvae in choice tests with dead larvae, but were not an effective defence against these species in Petri dish arenas. Larvae of O. v-nigrum had a smooth dorsal surface, were intermediate in terms of mandible size, but were the fastest moving, a trait that benefited their survival in intraguild combat. Larvae of H. axyridis were intermediate with respect to dorsal spines and speed of movement, but had the largest mandibles. This species was the most effective intraguild combatant among the coccinellids and the only one to successfully compete against C. rufilabris larvae of similar age. The speed, manoeuverability and long mandibles of C. rufilabris enabled them to impale coccinellid larvae at a relatively safe distance. The spines of C. coeruleus larvae impeded laterally oriented attacks by C. rufilabris, but did not provide sustained protection from repeated attacks. Success in these interactions appeared largely a function of offensive weaponry (mandible size and morphology) and speed of movement, although the role of dorsal spines as defensive structures was not ruled out. Rates of larval cannibalism were highest for C. rufilabris and largely mirrored the level of aggression observed in interspecific combat for each species.

The susceptibility of representative pyrethroid (cypermethrin, deltamethrin, lambdacyhalothrin, bifenthrin), organophosphate (chlorpyriphos, triazophos, profenophos) and new chemistry insecticides (spinosad, indoxacarb and emamectin) was investigated for 18 field populations of Plutella xylostella (Linnaeus) from three different zones in Pakistan. The LC50 (mg ml−1; 48 h) values of pyrethroids for various populations ranged from 0.19–1.88 for cypermethrin, 0.31–2.64 for deltamethrin, 0.08–1.16 for lambdacyhalothrin and 0.07–0.88 for bifenthrin. The LC50 (mg ml−1; 48 h) of organophosphates ranged from 0.52–5.67 for chlorpyriphos, 0.37–4.14 for triazophos and 0.03–2.65 for profenophos. The most probable reason for low toxicity of organophosphates and pyrethroids is the evolution of multiple resistance mechanisms; however, further studies are required to establish these mechanisms. When these same products were tested against a susceptible laboratory population (Lab-Pak), the new chemistry compounds were significantly more toxic than pyrethroids and organophosphates. The results are discussed in relation to integrated pest management and insecticide resistance management strategies for P. xylostella.

The Chinese citrus fruit fly, Bactrocera (Tetradacus) minax (Enderlein), is one of the major citrus pests in Bhutan and can cause >50% mandarin (Citrus reticulata Blanco) fruit drop. As part of the development of a management strategy for the fly in mandarin orchards, population monitoring and experimental manipulations were carried out to determine: (i) adult emergence period; (ii) adult phenology patterns; (iii) period of crop susceptibility; and (iv) period from fruit drop to pupation. In western Bhutan, adult flies emerge from the overwintering pupal stage in late April/early May. Most flies are mature by the end of May and it is inferred that mating occurs at this time: from the beginning of June males rapidly disappear from the population and by mid- to late June are rare or absent from traps. Mature females are present in the mandarin crop at the beginning of June, but very little oviposition occurs until mid-June, while most damage has occurred by mid-July. Initiation of oviposition into mandarins is almost certainly linked to crop phenology. Adult flies disappear from the orchard system during August. After fruit drop, larvae were recorded leaving the fruit to pupate within 13 days. The use of early to mid-season protein bait sprays and/or targeted use of systemic insecticides during the one month oviposition period, plus the removal of fallen fruit once every 10 days, are recommended as control strategies.

Three bioassays were used to examine the oviposition behaviour of the hoverfly, Episyrphus balteatus (Degeer) in which various stimuli purported to influence host assessment and choice were tested. Episyrphus balteatus failed to exhibit enhanced behavioural responses, terms of approaches and landings, to artificial leaves with the highest numbers of aphids, suggesting that females are merely responding to the colour of the artificial leaves. A density-dependent oviposition response was reported in a second bioassay using whole bean plants, although there an asymptotic relationship. Syrphid responses, which were measured by oviposition over a five-day period, were greatest towards those plants with the highest number of aphids. In a final series of trials, gravid female E. balteatus showed a behavioural preference for filter papers with the greatest honeydew concentrations (0.26 mg μl−1 honeydew). More time was spent in the treated areas and syrphids demonstrated more proboscis and ovipositor extensions in these treatments. These bioassays provided an opportunity to isolate some of the individual of decision-making by female E. balteatus during egg-laying behaviour. A greater understanding of natural enemy behaviour is essential before enhanced control of pest populations in the field can be established.