The probing activities of the most important leafhopper vector of maize streak virus, Cicadulina mbila (Naudé) (Hemiptera: Cicadellidae) were studied on different host-plants. Host preference was determined by giving the insects a choice of six plants, Digitaria sanguinalis, Zea mays, Zea perennis, Paspalum conjugatum, Oryza sativa and Saccharum officinarum (all Gramineae). Cicadulina mbila showed a strong preference for D. sanguinalis. Histological examination of plant tissues for salivary sheaths was used to reveal the preferred tissue. Cicadulina mbila tended to ingest from the phloem of its preferred hosts, and switch to mesophyll or xylem tissue on less preferred hosts. The suitability of each host was assessed by measuring the weight gain and amount of honeydew produced on each host by newly emerged adult females. Both parameters were greatest on the preferred host. Probing behaviour was also monitored electronically by recording the different waveform patterns produced when insects were probing, ingesting or not probing on the selected hosts. Cicadulina mbila probed less frequently, ingested longer and spent less time in non-probing activities on its preferred host, D. sanguinalis, although these responses were similar on maize and sugarcane. Rice induced poor probing responses and altered behaviour. This interpretation of the waveforms was supported by histological examination. As maize streak virus (MSV) is not found in phloem sieve elements, prolonged ingestion from sieve cells would not account for efficient acquisition from maize, which would require ingestion from other types of cells. D. sanguinalis was the host in which most ingestion from the phloem occurred, but it is the poorest source of MSV.

The effects of the chitin synthesis inhibitor triflumuron, 2-chloro-N-[[[4-(trifluoromethoxy)phenyl]amino]carbonyl]benzamide, on the housefly, Musca domestica Linnaeus were examined in the laboratory. A dose of 1 μg of triflumuron applied topically to adult females of M. domestica resulted in egg hatch inhibition greater than 95%. At doses below 1 μg applied topically to adult females, subsequent hatched larvae were also highly sensitive to triflumuron; 0.5 μg applied topically produced 25% inhibition of egg hatch, but of the larvae that eclosed, only 20% survived to pupation. Hence, a dose of 0.5 μg applied to adults gave a total mortality of 85%. The effects of a single topical application of triflumuron declined over time in a dose dependent manner. After a dose of 1 μg, <5% of the first egg batch hatched, however, after 14 days egg hatch had risen to >90%. Topically applied triflumuron was most effective in inhibiting egg hatch when applied to females less than 3 days old. After 60 min tarsal contact with 20% triflumuron suspension concentrate on poly cotton cloth, 100% egg hatch inhibition was maintained for up to 1 week. Lower contact times, or triflumuron concentrations, gave lower percentage mortalities. The results suggest that triflumuron has considerable potential as a control agent for incorporation into autosterilizing devices for housefly control. However, further work is required to develop delivery systems capable of transferring an effective dose to females under field conditions.

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.

Trioza vitreoradiata (Maskell), a native of New Zealand, has recently been noted feeding on Pittosporum spp. (Pittosporaceae) in south-western Britain, where it causes damage to windbreaks and nursery plants. Its economic impact and nomenclatural history are discussed, and modifications to published keys to adults and nymphs of British Psylloidea are suggested to enable its recognition.

The autumn migration of the rice leaf roller moth, Cnaphalocrocis medinalis Guenée, in eastern China was studied at two sites (one in southern Jiangsu Province and one in northern Jiangxi Province), using radar and aerial netting. It was confirmed that C. medinalis is a high-altitude nocturnal windborne migrant, with large numbers of moths taking-off at dusk and flying continuously for several hours. Migration was post-teneral and the females had immature ovaries. Maximum densities of the moths typically occurred between 250 and 550 m above ground, and layering was intense on some nights. Moth layers often occurred at an altitude where there was a wind-speed maximum. In early September, migrant C. medinalis from southern Jiangsu Province were carried on the winds in an approximately westward direction. However, the winds prevailing in late September and October took migrants from both sites towards the south-west or south. Forward trajectories for C. medinalis and other insects emigrating from northern Jiangxi during October indicated that they were able to reach the tropical rice-growing areas near the south China coast, where year-round breeding would be possible. Incidental observations on the migratory flight of other lepidopteran pests, including Mythimna separata (Walker), Spodoptera litura (Fabricius), Ctenoplusia agnata (Staudinger) and Agrotis ipsilon (Hufnagel) (all Nocturidae), Spoladea recurvalis (Fabricius) and particularly Omiodes indicata (Fabricius) (both Pyralidae) are presented.

The bruchid Bruchidius atrolineatus (Pic) causes significant damage to the stored protein rich seeds of cowpea, Vigna unguiculata, in the West African Sahel. Twenty varieties of cowpea were evaluated for susceptibility to attack by B. atrolineatus in the laboratory. The bruchid showed differential response to the seeds in terms of developmental period, percentage adult emergence, seed weight loss due to feeding by one larva, adult weight at emergence and life-time fecundity of females reared from them. Based on these criteria, IT85F-2205 and IT84S-275-9 were the least susceptible varieties. The development of B. atrolineatus was most significantly delayed in these varieties. The beetle larvae consumed less of their seed material and adults reared from them were smallest and least fecund. The varieties IT87S-1393, IT90K-391 and IT84D-460 also had relatively lower susceptibility to the beetle than others. In a no-choice oviposition experiment, B. atrolineatus females laid equally on all varieties. Percentage egg hatch on the different cowpea varieties did not differ significantly. The results are discussed in relation to previous reports on susceptibility of cowpea and other legumes to bruchids.

White peach scale, Pseudaulacaspis pentagona (Targioni-Tozzetti) (Homiptera: Diaspididae), was a serious pest of mulberry until it was the subject of a successful biological control programme in Italy at the turn of the century. Since the 1950s it has returned as a sporadic pest of commercial peach and, more recently, kiwi fruit orchards. We sampled white peach scale in an unmanaged mulberry orchard in coastal Campania over a 17 month period to measure the impact, relative abundance, and interactions of the parasitoids in the absence of pesticides. Sampled scales were dissected, and the immature stages of the parasitoids identified. Mean densities of white peach scale varied with month from 3–15/9 cm2 on primary (interior) branches and 15–100/1.5–2 m secondary (exterior) branch. The generalist ectoparasitoid Aphytis proclia (Walker) was most abundant, followed by two specialist endoparasitoids, Encarsia berlesei (Howard) and Pteroptrix orientalis (Silvestri) (all Hymenoptera: Aphelinidae). Primary parasitism also varied with month from 25–85% on primary branches and 20–90% on secondary branches. Parasitism on primary branches was inversely density-dependent, but was densityindependent on secondary branches. Low levels of superparasitism were generally observed in E. berlesei and P. orientalis (0–6%), but were higher in A. proclia (0–21%). Multiple parasitism of hosts by E. berlesei and A. proclia was fairly common (up to 24% of E. berlesei immatures were found sharing a host with A. proclia), and A. proclia was the probable winner of within-host competitions. The hyperparasitoid Azotus perspeciosus (Girault) (Hymenoptera: Aphelinidae) parasitized late pre-imaginal instars of all three primary parasitoid species. There was no significant difference in hyperparasitism of the three primary parasitoid species, but the rate of hyperparasitism was inversely related to the total density of primary parasitoids.

Development and survival of an erigonine spider, Erigonidium graminicolum (Sundevall) (Araneae: Linyphiidae), were studied at seven constant temperatures ranging from 15°C to 35°C. Plotting development rates (reciprocal of mean times for development) and survival rates (expressed as percentages) against the different constant temperatures indicated that E. graminicolum is well adapted to low temperatures, but sensitive to high temperatures. Juvenile development occurred over a wide range of constant temperatures, but the survival rate was low at the upper and lower extremes. All eggs died before hatching at the highest tested temperature (35°C). There were statistically significant differences between males and females in juvenile and pre-imaginal development times. Juvenile development time decreased as temperature was raised to 32°C, but increased at 35°C. The mean duration of pre-imaginal development (egg to adult) varied from 94.4 d at 15°C to 23.8 d at 32°C. Considering development rate and survival, the most favourable temperature range appeared to be 15–32°C. For all life stages, graphs obtained by plotting the reciprocal of development times against temperature could be described by the six-parameter rate function of Wang et al. (1982). Temperature-independent distributions of normalized development times were approximated by a cumulative Weibull function. Frequency distributions of development times changed with temperature; they were almost uniform at 15–20°C, more symmetrical at 25–28°C, and somewhat skewed to the right at 30–32°C. The sum of effective temperatures (SET), and lower development threshold (LOT), were established for all life stages of E. graminicolum. Survivorship curves varied with temperature and, on average, were Type III.

Field studies of orientation responses of the IIS-10.11 sibling of Simulium arcticum Malloch species complex and other simuliid species to host-mimicking cattle silhouette traps (CSTs) were carried out in the Athabasca region of Alberta, Canada. Simuliids were attracted to CSTs from downwind by a CO2 bait but very few were attracted to an unbaited CST. Passively searching simuliids tended to fly at lower levels than actively host seeking ones. Simuliids appeared to fly at lower levels when within visual range of the CST than when outside of it. Higher flight levels may improve chances of eventually making visual contact with the host or CST. Experiments in which a CO2 outlet was separated by increasing distances from a CST indicated that simuliids see the 1.1 m long CST at a range of approximately 8 m. Simuliids landing on the CST, whether CO2-baited or not, showed a strong preference for the trap's ends followed by the downwind side, followed by the upwind side. Species composition of collections from CST collections differed significantly from the species composition of cattle sweeps taken at the same times. Simulium vittatum was over-represented in collector catches in comparison to cattle sweeps. This bias may be due to species-specific differences in responses after landing on the CST since sweeps taken around CSTs had compositions similar to cattle sweeps. Results are discussed in terms of host orientation in biting flies in general and the suitability of CST-type traps as components of attractant-based control strategies and in simuliid population monitoring.

Based on a longitudinal survey performed in 1982–1983, a vector control strategy was implemented from 1985 onwards in a malarial-dense area of Burundi. One annual round of indoor spraying with malathion greatly reduced both the parasite load and the parasite rate in the population until 1989. However, from 1990 to 1993, a progressive resurgence of malaria was observed in most villages. For the present study, two villages were selected on the basis of their differential response to house spraying. In the village of Mulira surrounded by rice fields, the excellent results observed in the past have been followed by recent increases in parasite rates. In the village of Murengeza, also located in the rice growing area but near a river, the spraying had less impact. The inoculation rate was found to be similar in both villages, but the transmission peak occurred at the end of April in Mulira, and two months earlier in Murengeza. Indoor spraying with lambdacyhalothrin was carried out on 26 April 1993, one month too late according to the strategy intended. As no sporozoite mosquitoes were observed during the six months following spraying, this strategy should be maintained but, in villages near rivers, the application should commence much earlier, in mid-January. Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) and A. funestus Giles were found to be very endophilic species, whereas the dominant A. arabiensis. Patton was highly exophilic. Therefore it is recommended that treatments should not only be applied to human dwellings but also to other structures such as animal sheds, kitchens, etc, shown by earlier studies to be resting sites of A. arabiensis. This study underlines the need for regular reassessment in vector control programmes.

Studies were carried out to estimate and compare mortalities of larvae and pupae of Aedes (Stegomyia) simpsoni sensu lato breeding in axils of Colocasia esculenta, Xanthosoma sagittifolium (Araceae) and Musa spp. (Musaceae) in different locations in Uganda and also to ascertain whether there are any differences in their dynamics that could be used to separate the species. The probability of larvae surviving from one day to the next (40·5 – 99·8%), and the proportions dying in each instar (0·97 – 77·3%) and dying daily in all the four instars (3·9 – 46·3%) varied between seasons at each site and between sites and species of plants. Estimates of larval and pupal mortality were generally highest for fourth instar [52·4 ± 6·0% (mean ± SE)] and lowest for the second instar larvae (16·0 ± 2·6%). There was higher larval instar mortality in axils of X. sagittifolium (96·9%) and Musa spp. (82·2 – 96·5%) than in C. esculenta (47·1 – 88·4%).

DDT-resistant Anopheles gambiae Giles from Zanzibar, Tanzania, had increased levels of DDT-dehydrochlorination compared to a DDT-susceptible strain. Glutathione S-transferases (GSTs) are responsible for conversion of DDT to DDE in both the susceptible and resistant strains. Sequential column chromatography, including Q-Sepharose, S-hexylglutathione agarose, hydroxylapatite and phenyl Sepharose, allowed the partial purification of seven GSTs. All seven GSTs possessed different degrees of DDTase activity. There was an eight-fold increase in total DDTase activity in the resistant compared to the susceptible enzymes. Characterization with three substrates, 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB) and DDT, revealed the different substrate specificity for each isolated GST indicating different isoenzymes. GST Va possessed 60% of total DDTase activity suggesting that it contributed most to DDT-metabolism in this insect species. The DDTase activity of the GSTs in both strains of A. gambiae were found to be correlated with the GST activities toward DCNB. Preliminary studies on DDT-resistant and susceptible A. gambiae showed that both DDT-resistance and the increased levels of GST activity were stage specific which suggested that different GSTs may be involved in DDT-resistance in adults and larvae of A. gambiae.

Populations of the soil insects African black beetle, Heteronychus arator (Fabricius), and whitefringed weevil, Graphognathus leucoloma (Boheman), and the damage caused to potato crops in south-western Australia were measured with and without the insecticide chlorpyrifos incorporated into the soil prior to planting. Low populations of both insects were highly damaging. Destruction of stems by H. arator reduced tuber yield and both species damaged tubers from the time of their formation. Tuber damage increased with time because both insect species on average damaged multiple tubers and caused multiple attacks on tubers. Growth of G. leucoloma larvae caused increased abundance of the more damaging later instars in spring. The insecticide reduced resident H. arator abundance and hence damage to newly-emerging potato stems in summer, but had less effect on reducing attacks on tubers in summer crops because adult beetles flew into some crops during growth. Exceptionally high tuber damage per H. arator adult in winter crops was ascribed to enhanced activity during its spring breeding season. The insecticide was inconsistent in reducing the abundance of G. leucoloma larvae. Insecticidal effects were greatest near the soil surface, resulting in an increase in the relative proportion of both insects deeper in the soil. Since a greater proportion of the tubers occurred there, the resulting greater potential for the insects to cause tuber damage tended to outweigh reduction in their abundance.

Cryptolestes ferrugineus (Stephens) and C. pusillus (Schönherr) were reared separately at initial densities of 20 or 40 adults each and together at an initial density of 20 adults/100 g cracked wheat or cracked maize at 35, 30, 25, and 20°C and 70% r.h. for developmental periods of 10, 11, 16, or 40 weeks, respectively. Intraspecific competition in the 40-adult treatments restricted population growth to levels similar to 20-adult treatments for each species; impact was greatest for C. pusillus on maize at 30°, where the population of the 40-adult treatment was less than half that of the 20-adult treatment. Both species produced larger populations on wheat than on maize, except for C. pusillus at 35°C; mortality for both species was high on wheat at 35°C. Interspecific competition resulted in significantly reduced populations relative to single species populations for both C. ferrugineus at 30, 25, and 20°C and C. pusillus at 35, 30, and 25°C on wheat and for C. ferrugineus at 25 and 20°C and C. pusillus at 35, 30, and 25°C on maize. During interspecific competition, C. ferrugineus was more successful in multiplying at 35 and 30°C on wheat and 35°C on maize; both species multiplied equally well at 25°C on wheat or 30 and 25°C on maize; C. pusillus multiplied best at 20°C on both wheat and maize. Cryptolestes pusillus reproduces more effectively alone or in interspecific competition under cool conditions, although C. ferrugineus occurs with much greater frequency in cool Canadian stored grain, probably because of cold-hardiness and winter survival

Helopeltis pernicialis, a new species of bryocorine Miridae, is described from northern Australia, where it has become established as a serious pest of cultivated cashews, Anacardium occidentale (Anacardiaceae). Information on the biology and pest status of the bug is provided from studies conducted near Darwin, Northern Territory.

The use of the random amplified polymorphic DNA (RAPD) polymerase chain reaction to characterize individual Lucilia sericata Meigen from southern England was evaluated. Some simple techniques which allowed the preservation and extraction of DNA to be optimized without the complications of transporting liquid nitrogen were investigated. The RAPD results show that closely related L. sericata, including those from a single strike, can be readily distinguished from each other on the basis of their RAPD profiles resolved using electrophoretic analysis; profiles were defined with ten random primers. Analysis of these RAPD data using a similarity coefficient method and a recently developed randomization test to detect the non-random association of alleles at different loci, allowed the genetic homogeneity of L. sericata within southern Britain to be explored. This study shows that while a number of factors can complicate the use and interpretation of RAPD fragments as genetic markers, RAPD fingerprinting can be a valuable technique for studies of intraspecific genetic variation in L. sericata.

Uscana lariophaga Steffan is an egg parasitoid of the bruchid species Callosobruchus maculatus (Fabricius) and Bruchidius atrolineatus Pic in West Africa, which cause damage in stored cowpea (Vigna unguiculata (Leguminosae)). In a no-choice situation, the attractiveness of some odour sources to the parasitoid was studied in a simple diffusion olfactometer. Cox's proportional hazards model was used for data analysis. The results showed that cowpea beans were more attractive to naive U. lariophaga females than glass beads. Baits with host eggs were more attractive than baits without eggs. Experienced females did not perform any better than naive ones. The relationship between the inclination to fly of the parasitoids, and the baits used, was difficult to interpret. Changes in searching activity between the different weeks of experimentation were observed. Only a small part of this variation could be explained by (absolute) changes in barometric pressure.

Field experiments in which clip-caged apterae of Myzus persicae (Sulzer) (Homoptera: Aphididae) were monitored on sugarbeet revealed that leaf age, plant age and infection of the host with beet yellows closterovirus (BYV) had very large effects on aphid performance (development, reproduction and survival). On healthy plants performance was much better on young, expanding heart leaves than on older leaves. Performance on senescent leaves was poor. When apterae were kept on young heart leaves all their lives (by moving clip-cages to younger leaves every 4 days) there was a strong negative relationship between aphid performance and plant age (measured as plant leaf number at birth). On plants inoculated with BYV apterae showed large improvements in performance. These occurred so rapidly that nymphs born at the time of virus inoculation could benefit as much as those born later. The sizes and between-leaf distributions of M. persicae populations which developed from standard numbers of colonists on whole plants in cages were consistent with the results of the clip-cage experiments. Alatae were less sensitive than apterae to differences in plant and leaf age. Implications of the results for BYV epidemiology and control are discussed.

The influence of green ants, Oecophylla smaragdina (Fabricius), on insect pests of cashew, Anacardium occidentale Linnaeus, in tropical northern Australia was investigated using field surveys and field observations. Oecophylla smaragdina was abundant in the native vegetation of the area, and it was a dominant predator when found in cashew plantations. Oecophylla smaragdina significantly reduced the numbers of the four most important species of insect pests (Helopeltis pernicialis Stonedahl, Malipatil & Houston, Penicillaria jocosatrix (Guenée), Amblypelta lutescens (Distant) and Anigraea ochrobasis Hampson) on cashew trees, and trees with higher numbers of O. smaragdina produced higher quality nuts than trees with fewer numbers of O. smaragdina. Other ant species also reduced pest numbers, but not as much as O. smaragdina. The possibility of using O. smaragdina to control insect pests of cashew in the future is discussed.

Adult flies from five taxa (Bactrocera carambolae Drew & Hancock (formerly ‘Malaysian A’), B. dorsalis (Hendel) sensu stricto, B. melastomatos Drew & Hancock, B. papayae Drew & Hancock (formerly ‘Malaysian B’) and B. propinqua (Hardy & Adachi) of the Bactrocera dorsalis complex were analysed at 17 enzyme loci using horizontal starch-gel electrophoresis. Eleven loci—aAdh, Ald, Gpd, Ldh, aMdh, cMdh, Me, Pgm, Pgd, Sod-F, Sod-S—were represented by the most common allele in the five taxa. Of these 11 loci, seven showed intraspecific variation in one or more taxa. Among the five taxa, B. melastomatos could be distinguished from the rest by two loci (Acp and Gpi), while B. propinqua could be separated by four loci (Acp, Est-D, Idh90, Pep-C). Bactrocera dorsalis, B. carambolae and B. papayae did not possess any species-characteristic locus/allele, but B. carambolae could be distinguished from the other two taxa by Idh. The proportion of polymorphic loci in the Malaysian taxa ranged from 0.41 to 0.53. Bactrocera propinqua had the lowest average heterozygosity (H=0.05), while that in B. carambolae, B. melastomatos and B. papayae ranged from 0.09 to 0.11. The genetic identity values indicate closest affinity between B. dorsalis and B. papayae (I=0.99), followed by B. caramboiae (I=0.92), B. melastomatos (I=0.84) and B. propinqua (I=0.69). Bactrocera melastomatos showed closest affinity to B. carambolae (I=0.87) and was most distant from B. propinqua (I=0.64).