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.

McPhail traps baited with hydrolysed protein and borax to trap mainly female fruit flies, Jackson traps baited with trimedlure to attract male Ceratitis capitata Wiedemann, and Jackson traps baited with cuelure and methyl eugenol to trap Bactrocera spp., were hung in fruit trees at 50 sites and serviced weekly from June, 1994 to March, 1995, over an area of 350 km2 in Nicaragua. Samples of fruit were collected and kept separately to rear adult fruit flies and their hymenopterous parasitoids from known host plants. No Bactrocera spp. was trapped or reared from fruit at any site. Ceratitis capitata was caught in high numbers in McPhail and Jackson traps at nearly all sites in the dry season, attacking coffee berries and fruit of Citrus species. Toxotrypana curvicauda Gerstaecker was attracted to the food lure McPhail traps in low numbers and was widespread throughout the year, attacking papaya (Caricaceae). Of 29 Anastrepha species known to occur south of Mexico and north of Panama, ten were found during the study, occurring mainly in the rainy season; only two of them were trapped frequently and reared from collected fruit. Anastrepha obliqua Macquart proved to be the second most abundant fruit fly species, with a population peak from June to October when its preferred host plants Mangifera indica, Spondias mombin (Anacardiaceae) and Psidium friedrichsthalianum (Myrtaceae) were ripening. Anastrepha striata Schiner, trapped at 45 sites, occurred from June to November, attacking P. friedrichsthalianum and P. guajava. Sampled fruit of a further eight species in seven families were not attacked by tephritid flies. Parasitism by introduced braconid Diachasmimorpha longicaudata (Ashmead) was very low (3.7% in C. capitata, 2.7% in A. obliqua and 5.3% in A. striata).

Reciprocal crosses between strains of Aedes aegypti (Linnaeus) from different geographical areas have revealed an unexpectedly complex pattern of holandrically inherited male biased sex ratios in F2. The variation has been interpreted in terms of a web of X–Y interactions in Fl, in which the Y chromosome may or may not show meiotic drive against the X chromosome with which it is paired. The pattern of inheritance is not in agreement with a single form of Y chromosome, driving with different degrees of intensity against Xs of different sensitivity, but indicates different forms of driving Y chromosome. A rule has emerged that if Fl males from any cross give rise to a male distorted sex ratio in their progeny (F2), the males from the reciprocal cross give rise to a normal sex ratio. All eleven newly colonized strains from Ghana showed Y meiotic drive against the Xs of five strains, one of American and four of Australian origin, although one of the eleven showed a greater degree of drive than the other ten against the same sensitive strains. The variation observed is discussed in relation to previous studies on meiotic drive by the MD haplotype, and to the possible exploitation of sex ratio distortion in controlling this potentially dangerous insect.

Two of the most common and serious pests of maize and sorghum in the coastal areas of East Africa are the pyralid species, Chilo partellus (Swinhoe) and C. orichalcociliellus (Strand). Maize monocrop (with high and low plant density) and maize/cowpea mixed intercrop field experiments were conducted in Kenya to test if intercropping decreased the number of egg batches laid, altered the distribution of the egg batches and influenced egg parasitism. There was no significant difference in the number of egg batches per plant between treatments and the egg batches were randomly distributed on and among plants in most of the plots for all three treatments. There was a tendency for higher egg parasitism in the intercrop. The proportion of eggs parasitized was significantly correlated with total number of eggs per plot suggesting a positive density dependent response. It is concluded that intercropping does not affect C. partellus nor C. orichalcociliellus oviposition behaviour but egg parasitism is likely to be augmented.

Seasonal occurrence and abundance of redlegged earth mite, Halotydeus destructor (Tucker), was measured by weekly sampling in grazed annual pastures near Keysbrook (1990–1992) and Narrogin (1991–1992) in southwestern Australia. Mites were active for 27 weeks from the late autumn (May) to mid-spring (October), completing three generations at approximately 8 week intervals. The summer is spent as diapause eggs in the cadavers of adult female mites. In 1991 and 1992, active H. destructor was on average twice as abundant at Keysbrook (mean 11,300 mites/m2), as at Narrogin (mean 6400 mites/m2). Three times more eggs were laid at Keysbrook than Narrogin (mean 8500 and 2900 eggs/m2 respectively). Rainfall at Keysbrook was twice that at Narrogin, and temperatures were higher. We suggest that the rate of oviposition was less at Narrogin, probably because of resource limitation. The mature adult sex ratio was female biased, but was lower at Keysbrook (0.669) than at Narrogin (0.813). Neozygites acaridis, a fungal disease, was detected in less than 4% of the population, mainly in adult mites in late spring. Rainfall and temperatures were lower in the spring of 1992 than 1991 at both sites. Pasture was grazed considerably shorter in the spring of 1992, and numbers of H. destructor were lower, but numbers of eggs laid in the two years were similar. We suggest that active mite mortality was greater in spring of 1992, probably due to lower relative humidity. There were fewer adult mites in spring, and fewer diapausing eggs in summer at both sites in 1992 (36,600 diapause eggs/m2) than in 1991 (148,000 diapause eggs/m2). It is proposed that controlling mites in spring should lead to lower numbers of diapause eggs in summer and of mites emerging in autumn.

Nucleotide sequence variation and morphological characters were used to study the evolutionary relationships among nine tetranychid mites species. A phylogenetic study of this family based on mitochondrial cytochrome oxidase subunit I (COI) sequences had previously placed the species Tetranychus viennensis Zacher outside the other species analysed in the genus. Phylogenetic relations within the genus were re-examined with the addition of the species Tetranychus quercivorus Ehara & Gotoh, which is morphologically close to T. viennensis. Another region of the genome, the second internal transcribed spacer (ITS2) of ribosomal DNA, was also studied and proved to be of considerable interest at this taxonomic level. Both COI and ITS2 sequences indicated a close relationship between T. viennensis and T. quercivorus, which are grouped together and distinct from the other Tetranychus examined. The two species display morphological characteristics such as the absence of a medio-dorsal spur on all empodia of the legs of both sexes and the presence of anastomosing peritremes. This distinguishes them from the other members of the genus Tetranychus. The convergence of molecular and morphological data suggests that T. viennensis and T. quercivorus should not be classified in the genus Tetranychus. It is proposed that the genus Amphitetranychus Oudemans should be restored for classification of these species. Finally, a key to the Tetranychini tribe genera with one pair of para-anal setae is presented.

Adult olive fruit flies Bactrocera (Dacus) oleae Gmelin were exposed for 24 h to 25 × 10 cm polyester target devices, impregnated with 3% a.i. triflumuron (2-chloro-n-[[[trifluromethoxy]phenyl]amino]carbonyl]benzamide), a chitin synthesis inhibitor, formulated in 10% w/v sugar solution and air-dried. Treated insects were tested for egg hatch inhibition and larval mortality. Inhibition of egg hatch and F1 larval mortality depended on the sex exposed and the elapsed time after exposure. Egg hatch was reduced to 37.6% and F1 larval mortality reached 100% when both exposed sexes were mated. Exposure of one sex prior to mating resulted in a lower level of egg inhibition and larval mortality; but exposure of females was more effective at inhibiting egg hatch and larval survival than exposure of males in these crosses. In flies exposed once, the residual activity of triflumuron decreased gradually, fifteen days post-exposure egg hatch and larval mortality reached 62% and 44% respectively. Target devices aged under natural conditions reduced egg hatch to an average of 39% and inhibited completely larval development for a period of four months.

Morphometric studies of allopatric populations of the Cotesia flavipes species complex representing three putative species; C. flavipes Cameron, C. sesamiae (Cameron) and C. chilonis (Matsumura), were conducted. Sixteen characters were measured. Principal component analysis separated the complex into three somewhat overlapping groups that corresponded well with previous concepts of the species. Canonical variate analysis separated the complex into three distinct clusters with populations from Africa together, populations from Asia and the Neotropics forming a second cluster, and material from China and Japan forming a third cluster. The Mahalanobis squared distances between the three clusters were nearly equal. Results support recognition of three species in the C. flavipes complex.

A population genetic study of Halotydeus destructor (Tucker) and H. anthropus Qin & Halliday was undertaken using allozyme electrophoresis. Allele frequency data were collected from five polymorphic loci (Gpi—glucose phosphate isomerase, G6pd—glucose-6-phosphate dehydrogenase, Idh — isocitrate dehydrogenase, Mdh — malate dehydrogenase, and Pgm–phosphoglucomutase) to determine genetic variability and levels of gene flow among Australian and South African populations. The two species could be distinguished by the most common allele at Gpi and usually Pgm. There was no evidence for subdivision among the Australian populations of H. destructor, but the levels of substructuring among the South African populations of H. destructor and those of H. anthropus were high. The geographic origin of H. destructor is discussed; the evidence suggests that the original source of the Australian populations of H. destructor was from Cape Town, South Africa.

Local parasitoid populations may be adapted to their sympatric major plant host complex. Parasitoid strains may thus differ in their propensity to search for a particular micro-habitat or host or they may differ in their physiological compatibility with particular plant or host species. Cotesia flavipes Cameron, a larval parasitoid used worldwide in biological control against tropical stemborers, has a wide host range in diverse habitats. The existence of plant and/or host specific strains in C. flavipes has been postulated. To provide insight into the existence of strains in C. flavipes, we compared the plant/host complex selection behaviour, and physiological compatibility with different stemborers, of six different geographic strains of C. flavipes that differed in the plant/host complex they were obtained from. The results of the host selection experiments indicate that there is no intraspecific variation in host selection behaviour among C. flavipes strains. However, our comparative experiments show variation in reproductive success among strains. The most significant result was that the strain with the longest period of co-existence with the new host Diatraea saccharalis Fabricius had the highest reproductive success on this host species. We argue that the reported existence of C. flavipes strains is based not on differences in host selection behaviour, but on differences in physiological compatibility between local parasitoid and host population.

Gene diversity and gene flow in Glossina pallidipes Austen were studied by using allozyme electrophoresis on samples from southern and East Africa. Recorded were 30 alleles segregating at eight loci. Gene diversity was 0.212±0.085 S.E. in four southern African populations and 0.163±0.076 in seven Kenyan populations. All loci were in Hardy-Weinberg equilibrium. Pgm and 6pgd were sex linked. Spatial components of gene diversity were measured by using F statistics. Mating was random within each population. The ‘fixation index’ FST was 0.133±0.062 among southern African populations. Among the Kenyan populations. FST was 0.159±0.069. FST was 0.238±0.051 among all populations. Analysis of variance of gene frequencies showed that 65.8% of the genetic variance lay within populations and 34.2% of the genetic variance lay between Kenyan and southern African populations. These data suggest a strong measure of genetic drift among tsetse populations even in a region where it is thought they are continuously distributed. The causes of this drift require investigation.

Coprophagous beetles (endocoprid and paracoprid Scarabaeidae, Hydrophilidae, and Staphylinidae) were extracted from 698 sheep droppings from a pasture in southwest Germany. To quantify the pairwise niche overlap of these species, pairwise discriminant function analysis was used to calculate the overlap of the discriminant distributions in a four-dimensional niche space. Niche separation was studied considering the following four factors: season (month) and macrohabitat when and where the dropping was deposited, dropping size, and water content of the dropping. Multiple discriminant function analysis was used to describe the distribution of species in a space defined by four discriminant functions. The first discriminant function was mostly influenced by the factor ‘season’. The importance of different factors for niche separation in different functional groupings of dung beetles is compared with results from the literature. Advantages and disadvantages of pairwise and multiple discriminant function analysis, and univariate evaluation methods are compared. The following problems and restrictions of discriminant function analyses are emphasized: (i) the usage of non-numerical variables; (ii) the calculation of niche breadths; (iii) failures, when bimodally distributed variables are considered; and (iv) the ecological interpretation of statistical significances.

The aphid Therioaphis trifolii (Monell) is indigenous to the western Palaearctic region, where it colonizes lucerne (alfalfa), clovers and related legumes. A form of the species, T. trifolii f. maculata (the spotted alfalfa aphid, SAA), has been known in Australia since 1977, feeding almost exclusively on Medicago sativa (lucerne). Since 1989, T. trifolii has been found in Australia colonizing Trifolium subterraneum (subclover). We have compared samples of T. trifolii in Australia collected on lucerne and subclover using several techniques: survival and reproduction on different hosts, morphology, cuticular hydrocarbon profile, karyology, and a combination of RAPD-PCR and mitochondrial DNA (cytochrome oxidase) genetic markers. Whereas there were no distinct differences in cuticular hydrocarbons and karyology, we found significant correlated differences between the host on which aphids were collected, some morphological characters, and the genotypes of the aphids. Aphids collected from lucerne were always of one genetic type, and nearly all those from subclover were of another. Both groups of aphids are morphologically distinguishable from the yellow clover aphid (YCA), the other form of the species recognized so far. We conclude that the clover-colonizers (spotted clover aphid, SCA) and the lucerne-colonizers (SAA) are each host-restricted forms (biotypes) of T. trifolii. Estimates of mtDNA divergence are in the range of conspecific to closely congeneric, as compared with other insects including aphids. We developed simple diagnostic DNA tests to distinguish the two pest aphids.

Field studies on the response of Anopheles gambiae s.l. Giles and Anopheles funestus Giles to tents baited with human odour or carbon dioxide were conducted in south-east Tanzania. Two exit traps and a CDC miniature light trap set beside a bed net were used to sample mosquitoes that entered the tent. Human odour, pumped from an underground pit into a bed net attracted a similar number of mosquitoes as a bed net occupied by a human male. Significantly fewer mosquitoes were caught in a tent into which carbon dioxide (300 ml min-1) was pumped than in a human-odour baited tent (9 and 27% for A. gambiae s.l. and A. funestus respectively). A five-fold increase of the carbon dioxide concentration (to 1500 ml min-1) did not increase the catches of A. gambiae s.l. whereas those of A. funestus were increased to 69% of the catches by human odour. Species identifications of A. gambiae s.l. catches showed that A. arabiensis Patton prevailed and that the proportions of A. arabiensis/A. gambiae s.s. did not differ between treatments. It is concluded that in the indoor situation described, human odour other than carbon dioxide is the principal cue to which these malaria vectors are attracted and that the physical presence of a host and carbon dioxide, when used as a kairomone on its own, accounts for only a minor part of the overall attractiveness of man, particularly for A. gambiae s.l.

The blood feeding patterns of Anopheles freeborni Aitken and Culex tarsalis Coquillett were studied, and the effects of host availability on these patterns were assessed in four different habitats within a northern California rice agroecosystem. Resting mosquitoes were collected from June to September of 1991 and 1992. The source of mosquito blood meals was identified with the modified precipitin test. Anopheles freeborni exhibited a ‘specialized’ (fixed) blood feeding pattern, predominantly (99% of the time) feeding on mammalian hosts; leporids and bovids were the major hosts, while equines, suids, and other mammals were minor hosts. Culex tarsalis exhibited a more ‘generalized’ (catholic) blood feeding pattern, taking blood meals from both birds and mammals at a ratio of 3:1 with Passeriformes being the most fed upon host group. Human blood indices were under 3% for both mosquito species, and multiple blood meals were estimated at less than 2%. The host feeding patterns for both mosquito species differed among the four (riparian, rice, pasture and mixed) habitats. The host feeding pattern for C. tarsalis reflected the distribution of both mammalian and avian hosts available. On the contrary, the host feeding patterns for A. freeborni reflected the distribution of mammalian but not the available avian hosts. Overall, host availability may be an important determinant of population size of some mosquito taxa (e.g. A. freeborni) than others (e.g. C. tarsalis) in rice culture agroecosystems.

Encarsia pergandiella Howard is the most abundant parasitoid of silverleaf whitefly, Bemisia argentifolii Bellows & Perring, in south Florida vegetable fields and can contribute significantly to natural biological control of this and other whitefly species. However, quality standards, costs, and risks in commercial tomato production are high, resulting in frequent recourse to chemical control. Therefore, successful utilization of biological control could depend on compatibility of the parasitoid with selective insecticides. We tested a wide range of potentially selective insecticides, represented by a mineral oil, an insecticidal soap, a neem seed extract and synthetic and natural sugar esters, against eggs, first and third instar larvae, pupae and adults, using a pyrethroid, CaptureR (20 g bifenthrin/1 EC), for comparison. CaptureR residues on nymphs exposed to adult parasitoids reduced parasitization more than other materials tested, and were most toxic to all parasitoid stages. Mineral oil caused high mortality to immature parasitoids, and residues reduced parasitization of E. pergandiella. However, oil residues were much less toxic to adults if applied as a spray to leaf surfaces than as a dip to a leaf and especially glass surfaces. In contrast, the toxicity of CaptureR was high regardless of bioassay method. Neem extract, insecticidal soap and both sugar esters tested had little or no effect on E. pergandiella. These latter materials could be considered selective in respect to E. pergandiella and might be used to suppress B. argentifolii without decimating parasitoid populations.

Methods for dispensing tsetse attractants using sealed polyethylene sachets and bottles were studied in the laboratory and field. 1-Octen-3-ol (octenol), 4-methylphenol and 3-n-propylphenol were dispensed singly or as blends from sachets 25–200 cm2 in surface area and with a wall thickness of 0.06–0.32 mm; butanone was dispensed from polyethylene bottles. The release rates of attractants, assessed gravimetrically or by GC analysis of volatiles released, were independent of the amount present. The rates were related directly to surface area, inversely related to wall thickness and increased exponentially with temperature. With blends of the attractants, the release rates of the two phenols were directly proportional to the concentration present, but that of octenol showed an exponential dependence. A similar exponential effect was seen with blends of the attractants and an involatile diluent. For mixtures of chemicals, the ratio of the released components was not affected significantly by temperature, sachet size or wall thickness. Release rates from polyethylene sachets and bottles in the field varied 100-fold according to temperature differences related to the time of day, season, and degree of insolation. Day-degree models to predict the losses of attractants from a polyethylene sachet in shade or in full sunlight were highly correlated (r2 = 0.84 and 0.81 respectively) with observed losses. The practical implications of these findings are discussed.

Larvae of the pine beauty moth Panolis flammae (Denis & Schiffermüller) were reared in sleeve cages on five different seed origins (provenances) of pole stage Pinus contorta in the field in each of four years from 1985 to 1988. Survival varied significantly between the years. In those years when survival was high, Significant differences between tree provenance were not found. However, between provenance significant differences were found in larval weight and stage of development. In the years when survival was low, the results seen in good years were reversed. significant differences attributable to provenance were found but these were not reflected in significant differences between larval weight or development. In addition, there was a significant correlation between the proportion surviving and larval weight, which was not the case in those years where larval survival was high. The results are discussed in light of the pest status of P. flammea in Britain and in view of current silvicultural policies. The use of trees resistant to insect attack as part of an integrated pest management programme is highlighted and the need to coordinate laboratory and field studies so as to control for environmental variation discussed.

Diurnal activity patterns and host preference of Glossina fuscipes fuscipes Newstead were studied in forest and linear habitats along Lake Victoria shore, Kenya. The objective was to identify the preferred hosts of G. f. fuscipes, the emanations of which may be attractive to this species. Hourly catches of flies in biconical traps were related to changes in the weather and the prevalence of hosts in the vicinity of traps. Flies were mainly active between 0800 and 1600 h, with males peaking around 1100 h and females around 1300 h. Activity of flies correlated directly with light intensity and temperature, but indirectly with relative humidity. Humans, livestock and the monitor lizard, Varanus niloticus, were the predominant hosts, although a significant positive correlation with fly catches could only be established with the prevalence of lizards. Blood meal identification by microscopic and serological methods showed that 73—98% of G. f. fuscipes fed on monitor lizards irrespective of host prevalence, season or location. The significance and possible epidemiological importance of the relationship between G. f. fuscipes and monitor lizards are discussed.