Myosoma nyanzaensis sp. n. is described and illustrated, and is distinguished from the only other known Old World species, M. chinensis (Szépligeti) comb. n. (= Bracon chinensis Szépligeti). M. nyanzaensis is the first species of the genus to be described from the Afrotropical Region, where it has been reared as a gregarious ectoparasitoid of larvae of the pyralid moth Chilo partellus (Swinhoe) infesting maize and sorghum.

The performance of Cactoblastis cactorum (Berg) as a biological control agent of the cactus weeds Opuntia ficus-indica and O. aurantiaca was assessed by compiling life-tables for each host-plant, in both a summer and a winter generation, at a site in South Africa. Egg predation, mostly by ants, ranged from 54 to 74% and was significantly higher on O. aurantiaca than on O. ficus-indica. Larval mortality on O. aurantiaca was high during the summer generation (65%), possibly because of dehydration of cladodes. Survival on O. aurantiaca was 55 and 60% of that on O. ficus-indica in the summer and winter generations, respectively. Adult mortality, calculated from the life-tables, was 45 and 84% in the summer and winter generations, respectively. The most important components of mortality were natural enemies in the summer generation and weather-related factors in the winter generation. Host-plant-related mortality was not as great as was formerly supposed.

Adults of Musca vetustissima Walker that were caught when attracted to humans in the field responded positively in a later test when a hand was inserted in a cage, both in terms of proportion responding and time spent on the hand. Flies with a similar adult diet, whether of culture origin or the first-generation offspring of field-caught flies, responded similarly to the hand in the cage provided they were of similar size. A larger proportion of small flies than of large ones came to the hand, and stayed for longer periods. Large protein-deprived and dung-fed (suboptimal protein) flies had a nuisance value between 28 and 35 times as great as large blood-fed flies, while small blood-fed flies had a nuisance value 18 times as great. The nuisance value of small protein-deprived and dung-fed flies was between 61 and 67 times as great. Residence period on the hand increased with time in large protein-deprived flies but not in flies in the other categories tested. Few flies responded to the hand during the first 15 day-degrees C post eclosion, or when gravid or nearly gravid; the most responsive flies were in ovarian stages 0B, 1, 2 and 3. The implications of these results are discussed in terms of the fly nuisance levels experienced in south-eastern Australia.

Oviposition sites of Phlyctinus callosus (Schoenherr) in an apple and a nectarine orchard in the South Western Cape, South Africa, were investigated. No eggs were found on the fruit trees, only in different fractions of the orchard floor, viz. in orchard weeds, leaf litter and soil. Significantly more oviposition took place in plant material on the orchard floor than in the top 20 mm of the soil. Microscopic dissection of samples of such plant material revealed that females prefer to oviposit in confined or hollow spaces in moist, live or decaying plant tissue on the soil surface or in weeds comprising the cover-crop. P. callosus females favoured certain weeds above others for oviposition. The dispersion pattern of eggs in the cover-crop was contagious. The implications of the observed ovipostion behaviour in terms of control strategy, and for exploitation in a monitoring system for this species, are discussed.

Adults of Stomoxys calcitrans (L.) that fed on stroma-contaminated haemoglobin plus bovine serum albumin had normal survival, fecundity and egg hatch. Feeding on haemoglobin from which the erythrocyte membrane strome had been removed, together with bovine serum albumin, reduced fecundity to zero. The addition of membrane ghost preparation to a lipid-free haemoglobin and bovine serum albumin diet restored the essential nutrients for normal fly fecundity. For normal reproduction therefore, S. calcitrans adults require erythrocyte stroma.

In studies in Massachusetts, the population density of Brevicoryne brassicae (L.) was measured over the lifespans of two groups of kale leaves from maturation to senescence, taking into consideration aphid spatial pattern (in colonies or as isolated insects) and aphid size as large (adults), medium-sized (nymphal instars 2–4) or small (first-instar nymphs) individuals. Total aphid densities per leaf in both leaf groups showed similar patterns of initial increase followed by a decrease as leaves aged over the 3–4-week period of leaf survival. Aphid densities reached peak values of 8·14 and 8·64 aphids per leaf for the two leaf groups studied, and 65–67% of all aphids observed occurred in colonies. Host and parasitoid recruitment to the aphid and the parasitoid immature populations were measured using a modification of the technique of Van Driesche & Bellows (1988). Total host recruitments per leaf were 43·7 and 64·6 aphids for the first and second leaf groups. Parasitoid recruitment was 6·8–8·1 for the first leaf group and 8·2–15·8 for the second. Recruitment values indicated 15·6–18.6% parasitism for the aphid cohort on the first leaf group and 12·7–24·4% for that on the second one.

Infestations of the sugarcane pest Eldana saccharina Walker have been consistently serious in one part of the cane-growing belt of Natal, South Africa. Mortality in this region over seven years was estimated from moth catches in light traps, checked against population change measured from extensive larval counts, and plotted against climatic indices. The object was to construct a predictive model to illustrate mortality in other regions of the cane belt, to which infestations have spread in recent years. The spread southwards along the coast did not seem to have resulted from a decrease in natural mortality, but the spread to higher altitudes appeared to be due to lower mortality associated with warmer and drier years. The phenology of the insect and the effect of the annual harvesting cycle on phenology are discussed.

Designs for insecticide-impregnated screens based on combinations of two different colours were evaluated for their attractiveness to Glossina palpalis palpalis (Robineau-Desvoidy) in the Ivory Coast. Screens were tested with flanking panels of mosquito netting (flanked screens) and without such panels (simple screens), using electric nets to catch flies contacting cloth of various colours or mosquito netting. No flanked screen caught more flies than an all-blue single-coloured screen; flanked screens without blue portions generally had lower catches than those with blue portions. The majority of flies was always caught over the netting panels rather than over the cloth screens, although the proportions varied for different colours. Among simple screens, one half pthalogen blue and half ultraviolet-reflecting white caught 2·4 times as many female flies as an all-blue screen and 3·6 times as many as an all-white (ultraviolet-reflecting) screen. The basis for this synergistic effect is that blue attracts flies strongly to a position near the target (e.g. circling), while the white induces landing responses; in the blue-and-white simple screens, 77% of all tsetse landed on the white surface. Several other colour combinations in simple screens gave similar results to the blue-and-white screen for females flies, for example black-and-white, and one of the blue-and-light-blue combinations. For males, the best combination for simple screens was blue and black. In tests of different configurations of blue and ultraviolet-white on simple screens, most flies were caught using a diagonally-divided screen, the lower triangular portion being white and the upper one blue.

The value of damage thresholds in determining the need for insecticide sprays against Helicoverpa armigera (Hübner) on cotton was evaluated in 1984 and 1985 in eastern Tanzania. Spraying at thresholds of 10, 20, 40 and 80% damaged squares was compared against spraying on a recommended prophylactic regime of six fixed-interval sprays. In both years, spraying on damage thresholds reduced the number of insecticide applications from six to between one and five without significantly affecting control of H. armigera, seed cotton yield or overall levels of damage to cotton.

Studies were carried out at Jilaal Moogi, south-eastern Somalia, of the responses of Glossina pallidipes Austen to traps and targets. F3 traps caught three times as many tsetse as a biconical trap. Baiting F3 traps with acetone (released at 5–50 000 mg/h), butanone (10–50 mg/h) or octenol (0·05–5 mg/h) either alone or as mixtures did not affect the catch significantly. The catch was increased by 1·6 times (P<0·05) by releasing a mixture of 4–methylphenol (at 0–2 mg/h) and 3-n-propylphenol (0·04 mg/h), and by four times by releasing a mixture of acetone (500 mg/h), octenol (0·5 mg/h) and the two phenols. Baiting a target enclosed in an electric net with the combination of acetone, octenol and phenols increased the catch only 1·3 times, (P>0.05). Baiting an electric net plus target with natural ox odour increased the catch 1·8 times (P<0·05). A pthalogen blue (peak reflectivity = 40% at 450 nm) target caught 1·7 times as many tsetse as a black target (P<0·01) and a standard blue (reflectivity = 29%) target caught 7·4 times the catch of a yellow one (P<0·001). The results are compared with published data from Zimbabwe, Kenya and Mozambique, and it is noted that the level of response of G. pallidipes in Somalia to host odours is lower than elsewhere.

Static tethered flight was used under laboratory conditions to investigate the flight duration of Chilo partellus (Swinhoe). A flight mill was used to measure flight velocity. Mated females flew for a longer time than unmated ones. Females also flew for a longer time than males. Mated females were able to fly and lay eggs alternately for at least three nights in a row. Flight did not affect the number of eggs deposited by females. The results from the flight mill show that the mill is an accurate device to measure flight velocity. The airspeed of C. partellus proved to be 0.9 m/s, and there appeared to be no difference between the flight velocity of mated or unmated males and females.

Cassava intercropped with cowpea in Colombia had lower numbers of Aleurotrachelus socialis Bondar and Trialeurodes variabilis (Quaintance) per leaf and per plant than did monoculture cassava. These differences persisted for up to six months after harvest of the cowpea. These results are examined in light of the natural enemies hypothesis, which suggests that natural enemies may be favoured in diversified systems, thereby reducting herbivore load. In this regard, the effects of different cropping systems on the whitefly predator Delphastus pusillus (Le Conte) and on the combined action of the parasitoids Amitus aleurodinus Haldeman and Eretmocerus aleyrodiphaga (Risbec) are discussed. D. pusillus displayed a functional responce and was more abundant in monocultures than in intercrops. Predator:prey ratios were similar between treatments and so low that predation appeared to have little impact on whitefly numbers. Parasitism levels of Aleurotrachelus socialis were not affected by crop combinations. The data suggest that the activity of the natural enemies does not explain cropping system effects on cassava whitefly populations.

A strain of Aedes aegypti (L.) was collected in Rio Piedras, Puerto Rico, in 1987 and reared through to the F2 generation. The strain was shown to be heterozygous for resistance to a range of pyrethroids, but there was no evidence of organophosphate and carbamate resistance. Biochemical studies indicated that the pyrethroid resistance was not metabolically based. Electrophysiological studies at the neuromuscular junction of resistant insects indicated that a kdr (nerve insensitivity) type mechanism was operating in this strain. It is not known whether this mechanism was selected by earlier DDT exposure or by the recent ultra-low-volume applications of pyrethroids.

The taxonomy of species in the braconid subfamily Microgastrinae that parasitize the larvae of Diatraea in the New World is reviewed and a brief diagnosis of each species provided. Apanteles fredi sp. n. is described from Guatemala and its relationships discussed. Information on the distribution, host associations and range in variation of species is provided, along with a revised and illustrated key to facilitate their identification.

Helicoverpa armigera (Hübner) and H. punctigera (Wallengren) are major pests of cotton and other field crops in Australia. Using data on then abundance of males in pheromone traps at many sites over three seasons, the spatial and temporal variation in trap catch of both species were examined using Taylor's power law and spatial autocorrelation. The distribution of both species was highly clumped, both temporally and spatially. Regression Coefficients for the relationship of spatial mean to variance (bs) were similar to those for noctuids in general, while similarly derived temporal values (bt) for H. armigera fell towards the upper end of the noctuid range and those for H. punctigera well above the range given by Taylor & Woiwood (1980). Taylor and colleagues suggested that patterns of dispersion are species-specific and that they reflect density-dependent patterns of movement towards and away from centres of abundance. Although the relationship between variance and mean abundance for both spatial and temporal aspects of trap catches of Helicoverpa is well fitted by Taylor's power law, it is argued that these patterns of dispersion are a consequence of demographic and environmental stochasticity. Little need is to invoke specific density-dependent behaviours as the major factor responsible in this case. In addition, while Taylor's power law indicated both species had a similar clumped distribution, limited autocorrelation analysis suggested a random dispersion of pheromone-trap catches for H. armigera and small scale patchiness (over distances of 1–2 km) in trap catches of H. punctigera.

The development of infestations of Pseudaulacaspis pentagona (Targioni-Tozzetti) on passion fruit vines in Western Samoa was monitored at two sites over a period of 20 months, during which the aphelinid parasitoids Encarsia berlesei (Howard) and E. diaspidicola (Silvestri) were released. All vines were rated for P. pentagona infestations, and the female scale insects were counted on selected vines. At one site, the numbers of P. pentagona built up to over 10 000 adult females per vine before the parasitoids became established, and within one year 50% of the vines died. At the other site, where vines survived, an endemic coccinellid predator, Sticholotis quadrisignata Weise, kept populations below 3000 females per vine until the parasitoids became established. Biological control of P. pentagona was achieved at both sites eight months after the parasitoids were introduced. A model for interaction of P. pentagona and parasitoids predicted higher levels for parasitization than revealed by microscopic examination.