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.

Two experiments were conducted at Galana Ranch, Kenya, which examined, under natural conditions, the relationships between the number of tsetse flies (Glossina pallidipes Austen) attracted to cattle, the rate at which the cattle made defensive movements, and the feeding success of the tsetse. The most frequent defensive movements were skin ripples and tail swishes, while leg kicks were of intermediate frequency, and head and ear movements were infrequent. In one experiment, the rate of skin ripples, but no other type of defensive movement, was significantly correlated with the number of tsetse attracted to the cattle. The proportion of tsetse that engorged was significantly (P < 0.004) correlated with the rate of leg kicks, more weakly with the rate of head movements (P < 0.07), and uncorrelated with the rates of other types of defensive movement. In the second experiment, the rates of skin ripples, tail swishes and leg kicks were significantly correlated with the number of tsetse attracted to the cattle. The proportion of tsetse that engorged was again significantly correlated to the rate of leg kicks (P < 0.03), more weakly to the rate of head movements (P < 0.04), and unrelated to the rates of other types of defensive movement. In neither experiment was there a significant relationship between the number of tsetse attracted to the cattle and the proportion that engorged, suggesting that any density-dependent feeding success was too weak to be detected. In experiment 1, the relative fat content of the male G. pallidipes that fed decreased as the rate of leg kicks increased, suggesting that when hosts are more active the sub-sample of tsetse that feed, out of those that approach, is both smaller and hungrier. There was no detectable effect of host defensive behaviour on the bloodmeal size of male G. pallidipes.

The spectral sensitivity of the compound eye of the cabbage root fly, Delia radicum (Linnaeus), was measured using the electroretinogram (ERG) technique, at fifteen selected wavelengths between 340 nm and 670 nm. The form of the ERG was found to be diphasic in nature. A primary peak of spectral sensitivity in the UV (340–350 nm), and a smaller secondary peak in the blue-green region (460–546 nm) were found, together with a shoulder of sensitivity, representing a ‘pseudo-peak’ as reported for other Diptera, in the red region (630 nm). No significant differences were found between the dorsal and ventral regions of the eye. The peak response in the green region (546 nm) agrees well with existing behavioural data on colour attraction and visual discrimination of host plants by the cabbage root fly.

Adult Bemisia tabaci (Gennadius) were tested with imidacloprid in a bioassay method using systemically treated cotton leaves. The method was simple, robust and repeatable and provided baseline data for a laboratory and a number of recently collected field strains. The LC50 for imidacloprid susceptible strains was calculated to be 1.7 ppm and a concentration of 16 ppm determined as diagnostic for imidacloprid resistance. Ten strains of B. tabaci collected from the Almeria region of Spain showed significantly less mortality at the diagnostic dose than the susceptible strains. The intensive use of imidacloprid in the Almeria region is considered the reason for the occurrence of resistance in this locality. Resistance to organophosphates, pyrethroids and endosulfan in B-type and non-B type B. tabaci did not confer resistance to imidacloprid.

The cibarial armatures of Anopheles albitarsis Lynch Arribálzaga, A. aquasalis Curry, A. bellator Dyar & Knab and A. homunculus Komp are described for the first time. Ten to 15 minutes after blood feeding, higher levels of blood haemolysis were observed among A. bellator (14.9%) and A. homunculus (14.0%) mosquitoes which possessed type C cibarial armatures than among A. albitarsis (3.3%) and A. aquasalis (3.2%) which possessed type B cibarial armatures. In contrast, there were no significant differences among the four species in levels of extra-erythrocytic haemolysis when measured immediately and after one hour. The blood processing physiology observed for the four anopheline species is discussed at the enzymatic, mechanical and taxonomic levels as it relates to innate vector competence.

The leucaena psyllid, Heteropsylla cubana Crawford, can devastate plantings of Leucaena leucocephala (Leguminosae), an economically important tree species in the Pacific Islands, Southeast Asia, Australia, India, Africa, and elsewhere. The predatory beetle, Curinus coeruleus Mulsant (Coleoptera: Coccinellidae), has been introduced into many of these areas from Hawaii for biological control of the psyllid. In this study, collections of C. coeruleus were made from 11 populations on four islands in the Hawaiian archipelago to determine population structure and estimate levels of gene flow. Over all populations, a measure of population subdivision, θ was 0.095, and the estimate of Nem, the average migration rate, was 2.4. θ values for the individual islands were 0.02, 0.12, 0.24 and 0.05 for Kauai, Hawaii, Maui, and Oahu, respectively. Estimated levels of gene flow between populations were not correlated with geographic distance, therefore isolation by distance does not appear to be an important process structuring C. coeruleus populations. Gene flow estimates can be used to characterize dispersal capabilities in insects or other organisms released for biological control. In this case, the inferior dispersal ability of C. coeruleus likely limits its rapid widespread establishment during release programmes.

Autosterilizing devices, composed of 20×50 cm rectangles of white polyester cloth, baited with 50% w/v sucrose and impregnated with 10% suspension concentrate of the chitin synthesis inhibitor triflumuron, were suspended in two caged-layer poultry houses on a 6 ha farm near Bhubaneswar, Orissa Province, in north-east India. Populations of Musca domestica Linnaeus declined significantly over 6 weeks in houses in which the triflumuron-treated targets had been deployed. Following the removal of the targets from these houses, the M. domestica populations subsequently increased. No comparable changes were observed in a control poultry house in which an equal number of targets, dosed with 50% w/v sucrose only, were suspended. Laboratory evaluation of the sugar-baited triflumuron targets confirmed that exposure of the strain of M. domestica present in the poultry manure to triflumuron-treated targets reduced egg hatch to less than 1%. There was no decline in the quantity of triflumuron present on targets during their 6 week exposure in the poultry houses, as shown by gas chromatography. Furthermore, a laboratory bioassay demonstrated no decrease in the potency of the chemical over the exposure period. However, the quantity of sugar present on targets decreased significantly after only 3 weeks exposure. However, populations in the treatment houses were not eliminated and immigration from surrounding houses may have reduced the effectiveness of the technique. The results are discussed in relation to the use triflumuron-treated targets as a practical autoster-ilizing system for house fly control in livestock production systems.

Eggshell peroxidase (ESP) is responsible for the hardening process in several Diptera, including Drosophila melanogaster Meigen and Bactrocera oleae Gmelin. Its action can be inhibited by phloroglucinol, a natural phenolic substance, during the formation of the egg-shell. We used phloroglucinol, in the diet of adults of D. melanogaster and B. oleae, at concentrations of 1 mM, 10 mM, 25 mM, 50 mM, 100 mM and 400 mM to study its effect on egg laying. In both insects, 1 mM had no effect. At concentrations above 10 mM, egg laying of D. melanogaster was gradually affected leading to the deposition of empty shells and chorion-less eggs, while in B. oleae, it was gradually suppressed and only amorphous masses were laid. The effect of phloroglucinol at the tested concentrations was reversible. It is concluded that phloroglucinol added at appropriate, non-lethal concentrations, affected egg-laying of D. melanogaster and B. oleae in different ways, related to differences in the ovipositor diameter relative to egg size. In B. oleae, it is relatively narrow, causing breakage of the phloroglucinol-induced non-elastic egg-shell, since covalent crosslinking of the chorion proteins is prevented. In D. melanogaster, chorion-less eggs and separate chorions are laid, due to egg dechorionation. A possible field application of these results is discussed.

The response of populations of the saw-toothed grain beetle, Oryzaephilus surinamensis (Linnaeus) (7022/1 strain), to insecticide treatments of different extent and standard concentration was studied over 16 weeks (no more than two generations) in experimental bins containing a wheat bulk and 16 kibbled wheat-filled refuges. Populations comprised initially low frequencies of resistant phenotypes, as would occur in natural populations where resistant alleles had newly arisen. The degree of control achieved was related to the extent of treatment. Distribution of adult beetles was greatly influenced by the effects of insecticide treatment superimposed on intrinsic microhabitat preferences. Live beetles were recovered from all bins, although numbers sampled from wheat bulks of treated bins were 1–6% of that of the untreated bin. More live beetles were sampled from wheat bulks than were recovered from all respective refuges, except in one treated bin. Live beetles were more numerous in refuges in corners and in those furthest from refuges on treated walls. Beetles were more likely to die in refuges in coiners and lower down in the bins or in refuges on treated walls adjacent to untreated walls. Although treatments produced heavy mortality, the frequencies of resistant individuals did not increase significantly. This could either be because treatments were equally successful in eliminating homozygous susceptible and heterozygous individuals, or because selection in favour of resistant individuals was too weak to be detectable, especially if there were negative correlations between viability and fecundity. Significant genetic structuring of refuge subpopulations with respect to the resistance phenotypes was noted and appeared to be related to behavioural preferences for microhabitat.

The ecology of Microtermes subhyalinus Silvestri in savanna and an adjoining sugarcane plantation in the Central African Republic is described. Other species of termites were associated with savanna and sugarcane but M. subhyalinus was the most prevalent and the only one causing damage to sugarcane. Damage to the crop by M. subhyalinus was assessed throughout the year. Termite attacks were confined initially to the root system just after cutting but as the cane matured and growth ceased, termites tunnelled up into the above-ground stems. Losses accounted for 5–10% of total annual production. The nesting and foraging behaviour of this species altered with the change from natural savanna to sugarcane cultivation. The vertical distribution of M. subhyalinus fungus combs in soil under savanna and sugarcane over different seasons was analysed. There was a linear relationship between monthly rainfall and foraging activity in savanna while in sugarcane no relationship was observed.

The Palaearctic pine aphids, Eulachnus agilis (Kaltenbach) and Eulachnus rileyi (Williams) have both been introduced into other continents where they have been reported causing damage to economically important pines. In Euorpe, they are attacked by the specialist parasitoid Diaeretus leucopterus (Haliday) which has been suggested as a possible biological control agent. Here we report on several aspects of the ecology of the parasitoid, conducted on E. agilis in Germany in 1993–94, to provide a more scientific basis for judging its potential for use in biological control. Parasitism of all instars in the field rarely exceeded 10% and was independent of host density. A high percentage of parasitized aphids were hyperparasitized. Measurements of the impact over 16 weeks in a greenhouse-release experiment showed that parasitism rates increased from 2 to 19% but were insufficient to suppress the aphid population below a damaging level. There was evidence of a density-dependent response. Studies on foraging behaviour showed that female parasitoids searched pines by quite extensive walks. There was no relationship between the number of aphids per tree and number of ovipositions, and the mean number of ovipositions per female per tree was 2.5 ± 0.4 eggs. The majority (55.1%) of encountered aphids did not respond to the parasitoids. However, female parasitoids attacked a much higher proportion of aphids that did respond but oviposition success on this group was poor. The number of aphid-infested needles on seedlings increased significantly owing to the parasitoid's foraging activity. On the basis of these results, it is suggested that D. leucopterus is only likely to be of benefit in biological control if used in conjunction with other complementary natural enemies.

Spider mites, Tetranychidae, represent one of the most cosmopolitan and economically important groups of terrestrial arthropods; however, many aspects of their evolutionary relationships remain uncertain. We sequenced part of the mitochondrial cytochrome oxidase subunit I (COI) gene in 20 species of phytophagous mites belonging to nine genera and two families (Tetranychidae and Tenuipalpidae), including several agricultural pests. As eported in insects, the sequences were extremely rich in A + T (75% on average), especially in the third codon position (95%). However, one of the genera we studied had a significantly lower A + T content (69% on average, 78% in the third codon position), showing that base composition can change substantially over short periods of time. Most interspecific differences were transversions and their number increased steadily with the number of non-synonymous differences, while the number of transitions remained constant. The phylogeny based on COI sequences was inferred using the maximum likelihood method. The results are compatible as a whole with the traditional classification based on morphological characters, but call for some minor taxonomic revisions. Some morphological characters and life history traits (mode of reproduction, adaptation to the host plant) were also analysed within this phylogenetic framework. At the family level, one can see a trend towards thelytoky becoming rarer compared to the general mode of reproduction of the group, arrhenotoky. There is also an evolutionary tendency towards a more complex mode of life, with the production of silk webs and correlated changes of the locomotion apparatus. However, in the Tetranychidae there seems to have been convergent evolution of these morphological characters together with independent development of a common adaptation to this mode of life in different genera.

Morphological studies of different populations of what was previously considered to be a single species, Aphanogmus hakonensis Ashmead, revealed the presence of a complex of species which are extremely difficult to distinguish without detailed studies of male genitalia. Several of these species have been misidentified during biological control programmes or parasitoid surveys. These misidentifications are corrected, and two new species, Aphanogmus captiosus and Aphanogmus thylax are described. The hakonensis-complex is diagnosed. As far as is known, all species are hyperparasitoids of lepidopteran larvae via various hymenopteran or dipteran primary parasitoids.

In Peninsular Malaysia, 18 species of hymenpterous parasitoids were reared either from the oil palm bagworms, Metisa plana Walker and Mahasena corbetti Tams, or from their parasitoids. Both Metisa plana and Mahasena corbetti share the common parasitoids Goryphus bunoh Gauld, Aulosaphes psychidivorus Muesebeck, Brachymeria carinata Joseph, Narendran & Joy, Eupelmus catoxanthae (Ferrière), Eurytoma sp., Sympiesis sp., Tetrastichus sp., and Aphanogmus thylax Polaszek & Dessart. Other parasitoids are associated with only one of the bagworm species: Paraphylax varius (Walker), Dolichogenidea metesae (Nixon), Elasmus sp., Nesolynx flavipes Ashmead, Pediobius anomalus (Gahan), Pediobius imbreus (Walker) and Teleopterus sp. from M. plana; and B. lasus (Walker), B. lugubris (Walker) and P. elasmi Ashmead from Mahasena corbetti. A key to species is included and a table summarizing the host range and distribution records are listed from the Indo-Australasian region.

The present paper revises the Australian and South African species of Halotydeus Berlese. The redlegged earth mite H. destructor(Tucker) is redescribed, and four new species are described (H. anthropus, H. bakerae, H. castellusand H. spectatus). A key to species is provided. Halotydeus destructor is an important pest of leguminous pasture and other crop plants, but the three Australian species (H. bakerae, H. castellus and H. spectatus)occur in native vegetation and are not believed to be of any economic significance. The pest status of the South African species H. anthropus has not yet been determined.

The above-water food webs of arthropod communities in irrigated rice fields on Luzon Island, Philippines, were studied over the growing season at five sites (Los Baños, Cabanatuan, Bayombong, Kiangan, Banaue) ranging in elevation from 22 m to 1524 m. Arthropod populations were vacuum-sampled at roughly weekly intervals from the date after seedlings were transplanted to flowering at each site. Site- and time-specific webs were constructed from a 687-taxa cumulative Philippines web and time-series of species present. Taxonomic composition, food web structure, and arthropod phenology were broadly similar across different sites. Arthropod abundance was inversely associated with altitude across the five sites, but numbers of taxa and links and six food web statistics showed no obvious increasing or decreasing trend with altitude. The rise of taxa, links and mean food chain length over the growing season at each site reflected an increase in plant size with age and, at some sites, an orderly accumulation of newly arriving herbivore, predator, parasitoid and omnivore species. At each site, herbivores built up faster than predators and parasitoids, and predators arrived faster than parasitoids; the difference between the latest and earliest sampling dates of first arrivals, averaged over the five sites, was 38, 63 and 73 days for herbivores, predators and parasitoids, respectively. Site-to-site consistencies in food web properties and first arrivals suggest that such patterns may be influenced more by crop age than by geography or altitude. Sampled predator, parasitoid and omnivore taxa potentially encountered only a subset of their lifetime prey and predator species at any particular time in the rice field. Prey lists cumulated over time may underestimate the temporal specificity of predation by potential biological control agents. Research opportunities linking rice food webs and integrated pest management with East Indies biogeography are proposed.

The relationship between abundance of Dolichoderus thoracicus (Smith) and damage to cocoa pods caused by Conopomorpha cramerella Snellen was examined in a series of experiments. Pods were harvested from ant-abundant and ant-scarce plots and categorized into fully extractable, partially extractable and unextractable, the last category reflecting the most severe degree of C. cramerella infestation. An abundance of D. thoracicus was associated with significant reductions in the percentage unextractable pods but had little or no influence on the other two categories. Mean percentage pods infested was generally kept below 50% in ant-abundant plots and mostly exceeded the 50% level in ant-scarce plots. Other studies were: a survey of individual pods relating rate of infestation by C. cramerella to D. thoracicus abundance, an experiment which examined the effect of D. thoracicus exclusion on the rate of C. cramerella infestation, and a count of exit holes made by emerging prepupae of C. cramerella in relation to varying degrees of D. thoracicus abundance. The results showed a clear negative effect of D. thoracicus abundance on C. cramerella infestation rate. The results also indicated that the protection conferred by D. thoracicus was largely confined to the particular pod on which it was present. Rat damage, monitored as a subsidiary study, was higher in ant-scarce plots throughout the study period.

A significant effect of moon phase on light-trap catches of Anopheles species was observed during a longitudinal study carried out in a forested belt of Madhya Pradesh, India, inhabited by tribal people. However, moon phase does not seem to have any effect on the proportion of adult Anopheles culicifacies Giles in the total catch, or the parity rate in this species, which is the vector responsible for perennial transmission of malaria in the area.