Chilocorus nigrita (Fabricius) is a well-known predator of scale insects. It has been widely used for biological control and has spread naturally beyond its previous native range over the last three decades or so. Three other Oriental species closely resembling C. nigrita can now be separated. Chilocorus melas Weise is redescribed and a lectotype designated. Chilocorus gressitti Miyatake is a junior synonym of C. melas. Chilocorus subindicus from the southern parts of the Indian subcontinent and C. gracilior from eastern Indonesia are described as new.

African cassava mosaic virus (ACMV), vectored by the whitefly, Bermisia tabaci (Gennadius), is considered the most damaging pathogen of any African crop. Information about vector movement is important for understanding the epidemiology of this disease and the experiments reported here were designed to examine B.tabaci flight activity both in and around a cassava crop in relation to time of day, crop growth stage, wind direction and speed, and to the resulting pattern of infected plants within the field at harvest. At wind speeds of <0.4 ms−1 adult B. tabaci approached the yellow traps by flying upwind. At greater wind speeds, significantly fewer B. tabaci adults approached the traps from downwind, thus reversing the directionally of the catch. When the direction of the prevailing south-west wind reversed, so did the directionality of the catch. Bemisia tabaci adults were flight active throughout the day and the greatest percentage were caught above the canopy between 06.00–08.00 h, when wind speeds were lowest. Trap height and position significantly affected catch with the greatest numbers caught on the lowest traps. More than three times as many B. tabaci adults were caught on traps situated downwind from the field compared to those upwind. Suggesting that the field was acting as a source of whiteflies. In both years, Africa cassava mosaic disease (ACMD) incidence was highest and lowest, respectively, on the edges and in the middle of the trials, with the highest incidence occuring on the edges facing the prevailing wind direction. These results are discussed in relation to the epidemiology of ACMD and to potential cultural control methods such as the use of ACMD-resistant guard rows to protect a mainly susceptible crop.

Despite the large number of collection rocords available, there has recently been some debate concerning how host-specific ticks are. A quantitative data set is presented for the host preferences of African ticks. The results are based on 43,615 individual collection records from published sources covering most countries in mainland Africa. Out of 223 ticks species, 112 have been collected 20 times or more; 14 of these are generalists and at least 39 are potential specialists. Further collections are needed for greater clarity in many cases. It is important that people working on problems that relate to tick-host interactions are aware of the context in which these occur, lest they make false a prior hypotheses about the importance of hosts or parasites in the system.

The seasonal abundance and rates of parasitism of three species of Mesoclanis seed flies was studied in South Africa. The three species occur on Chrysanthemoides monilifera, and were recorded during most months of the year, whenever C. monilifera was flowering. At three sites in KwaZulu-Natal, numbers of eggs per capitulum of Mesoclanis polana Munro were highest on C. monilifera rotundata between June and November (winter/spring), towards the end of the main flowering flush. Parasitism of M. polana was between 50% and 90% for most of the year. Two other species of Mesoclanis (M. magnipalpis Bezzi and M. dubia Walker) occurred together on C. m. rotundata in the Eastern Cape (St Francis Bay), where parasitism during the year was between 55% and 95%. Peak numbers of eggs per capitulum (M. magnipalpis and M. dubia combined) occurred in May/June (winter), in the latter part of the main flowering flush. Mesoclanis magnipalpis was the only species recorded on C. m. pisifera in De Hoop Nature Reserve (Western Cape), where there was only one peak of oviposition (May/June), coinciding with the short and discrete flowering period of this subspecies. Parasitism was between 50% and 65%. At least nine species of parasitoid were reared from immature Mesoclanis stages. Eurytoma sp. (Eurytomidae) was a dominant parasitoid at all sites. Results are discussed in relation to the possible effectiveness of species of Mesoclanis seed flies as biological control agents of C. monilifera in Australia.

A study was conducted in 1990–1995 in Canterbury, New Zealand to describe the phenology and seasonal abundance of all stages of the Argentine stem weevil Listronotus bonariensis (Kuschel), a New Zealand pest of Gramineae. Of note were major fluctuations in the densities of all stages from one season to the next which were not explained directly in terms of the availability of Neotyphodium lolii-free ryegrass tillers. The overwintering mortality rates of L. bonariensis were found to be linear and remarkably similar between seasons and locations in the absence of pathogens. This study also showed that care must be taken in the use of existing data to analyse the impact of the recently introduced South American parasitoid wasp Microctonus hyperodae Loan as a biological control agent of L. bonariensis; errors may exist because of earlier sampling biases. In spite of the confounding effects of seasonal variation in the L. bonariensis population, reduction in the size of the L. bonariensis first summer generation egg and larval peaks coincided with a build up of M. hyperodae.

A method is described for optimizing models by linking simulation procedures with a non-linear regression programme. It is then possible to work towards a parsimonious model which contains those, and only those, variables required for an optimum fit. Using the observed values, and the predicted values from each simulation, the optimizing routine calculates the value of an appropriate loss function. It then makes small changes in the parameters governing the simulation, recalculates the predicted values and the first and second derivative of the loss function with respect to each parameter. The algorithm uses this information to minimize the loss function for a given formulation of the model. The model is improved by adding variables which can be shown statistically to improve the fit, and by removing those which do not. The use of the technique is illustrated with reference to a series of weekly estimates of the total numbers, births and survival probabilities of a population of male and female tsetse flies Glossina morsitans morsitans Westwood. Simulation involved following the lives of cohorts of flies, and of all their progeny, from the time they were deposited as larvae. Development and reproduction were regarded as fixed functions of temperature, but mortality rates of pupae and of adult flies depended on meteorological and biological variables, plus the level of trapping imposed on the population. Potential factors were added singly and the model thereby improved in an objective, stepwise manner. The best fit was achieved when effects on adult survival due to maximum temperature, various modes of trapping, and an annual cycle were included in the model. The optimized simulation technique has been used here in improving a model which describes a biological population but it could equally be used to improve models in any situation where data are fitted using simulation procedures.

Comparative bioassays of two chloronicotinyl insecticides, acetamiprid and imidacloprid, against the whitefly Bemisia tabaci (Gennadius), using foliar and systemic applications, were conducted under laboratory conditions and in field trials. Under controlled conditions, the ovicidal activity of foliar applications of acetamiprid on cotton seedlings was much higher than that of imidacloprid. According to LC50 and LC90 values, acetamiprid was 10- and 18-fold more potent than imidacloprid. Both compounds were effective when applied to soil against whitefly adults; however, the potency of imidacloprid was somewhat higher than that of acetamiprid 2, 7 and 14 days after application; resulting (with the concentration of 25 ml a.i./l) in adult mortality of 90, 93, and 96% and 76, 84, and 76% respectively. In an experimental cotton field, the efficacy of foliar applications of 60 g a.i./ha acetamiprid and 210 g a.i./ha imidacloprid was compared. Field residual activity of acetamiprid to whitefly adults lasted for approximately ten days, compared with three days for imidacloprid.

Flight and surface activity of the African black beetle, Heteronychus arator (Fabricius), detected by pitfall, light and window traps, was seasonally reversed. High surface activity relative to flight occurred in spring when beetles were mature, while relatively higher levels of flight occurred in autumn when they were immature. Pitfall trap captures were male-dominated in spring and female-dominated in autumn, and were a poor estimator of adult density. Light trap captures were consistently female-dominated. Although autumn flight was dispersive and inferred to have some role in population regulation, it was largely localized within the usual pasture habitat of the species. Some beetles flew into irrigated potato crops in autumn, but not specifically, as beetle abundance was consistently less than in surrounding dry pasture. High surface activity indicates spring is a strategic time for surface-applied control measures to prevent increase of H. arator in the next generation, a less disruptive alternative to conventional soil-incorporated insecticide directed at the new generation's larvae in summer. Such an approach would be best aimed early in the upsurge of activity, as most of the season's cohort of eggs was laid by the time surface activity peaked in mid-spring.

Surveys of egg pods of agriculturally important grasshoppers were carried out in northern Benin between 1992 and 1995. Searches were made of oviposition sites under shrubs of the perennial legume Piliostigma thonningi along field margins. In 1993 and 1995, surveys were extended to include sorghum, Sorghum bicolor, and the perennial thatch grass Vetiveria nigritana. The four principal grasshopper species found at these oviposition sites were Hieroglyphus daganensis Krauss, Cataloipus fuscocoeruleipes Sjöstedt, Kraussaria angulifera (Krauss) and Tylotropidius gracilipes Brancsik comprising 86% of 4545 identified egg pods while 651 egg pods could not be identified to species level. Predation by meloid beetles (Epicauta, Mylabris and Psalydolytta spp.) varied between 0 and 50% for the four dominant grasshopper species. From 1993 and 1994 data, nymphal eclosion from egg pods damaged by meloids was significantly lower than emergence from undamaged egg pods. The hymenopterous parasitoids Scelio africanus Risbec and S. mauriticanus Risbec were reared from the four dominant grasshopper species and parasitism levels of 0.0–3.3% were recorded from these hosts. There were significant differences in nymphal emergences between parasitized and unparasitized egg pods of H. daganensis.

Host-feeding by parasitoid wasps has been viewed as a positive attribute for biological control, because hosts are killed as a result of host-feeding in addition to parasitism. Host acceptance and host-feeding responses o unparasitized vs. conspecifically parasitized hosts by the parasitoid wasp Itoplectis naranyae Ashmead were studied in the laboratory. Female I. naranyae selected to oviposit in unparasitized hosts and those that had been parasitized I h previously, in equal proportions, even when allowed access to both types of host. Females also fed upon both types of host equally. Females, however, avoided ovipositing in hosts parasitized 40 h and 70 h previously, and preferentially fed upon them when allowed access both to parasitized and to unparasitized hosts. Parasitoid progeny in hosts which had been used for host-feeding suffered a high degree of mortality. Females used host internal changes as cues for deciding whether to feed on hosts. It is suggested that immature parasitoid mortality can be increased due to female preference for using parasitized hosts for host-feeding. Hence, host-feeding by I. naranyae may not be an advantageous biological control characteristic. The adaptive significance of selective host-feeding is also discussed.

At least 62 species of ants were caught at baits in Philippine rice fields, notably in the bunds (levées) of irrigated rice. Many were relatively uncommon or localized. Apart from the ubiquitous Tapinoma sp. nr indicum Forel the most widespread was the aggressive Solenopsis geminata (Fabricius) which was often very abundant in fields with bunds that were disturbed by regular repair. This ant was scarce or absent in relatively undisturbed well-vegetated bunds where Pheidole spp. were sometimes common and where up to 14 different species were recorded in bunds of a single field. Colonies were spaced out along the bunds where foraging territories sometimes overlapped, except for those of the competing dominants S. geminata and Pheidole spp. In general, S. geminata retained its overall foraging areas from year to year but those of non-dominant ant species could vary considerably. Bunds of low-lying fields that are deeply flooded in the wet season were recolonized by S. geminata in the wet season. This ant occurred as separate colonies with workers from nests that differed in degree of mutual aggression. Such aggression was not observed in foraging areas. Solenopsis geminata and other species foraged into, and nested within, dry fallowed fields after the crop was harvested. In the crop season, they foraged across mud during periods of up to one week when farmers allow irrigated rice fields to drain before flooding. Solenopsis geminata workers also foraged across the closed crop canopy. At such times they were commonly observed preying on hemipteran and lepidopteran pests and on eggs and young golden snails (Pomacea canaliculata Lamarck) which are serious rice pests in the Philippines.

The Australian cotton industry relies almost exclusively on synthetic insecticides for control of early season pests. These insecticides often disrupt predatory insect activity in the field. Potential predators of the twospotted spider mite, Tetranychus urticae Koch, in cotton, identified in field and confirmed in laboratory experiments, included a theridiid spider, a phytoseiid mite, a lacewing larva, predatory thrips, several Coccinellidae and several Hemiptera. These predators were mostly generalists, having previously been reported as predators of aphids or caterpillars of Helicoverpa spp. The effect of insecticides on T. urticae and its predators was evaluated in three field experiments. Cotton was artificially infested with T. urticae then sprayed five times at seven to ten day intervals with either dimethoate (140 g ai/ha), thiodicarb (750 g ai/ha and 187.5 g ai/ha), endosulfan (735 g ai/ha and 367.5 g ai/ha), methomyl (169 g ai/ha) or amitraz (400 g ai/ha). Tetranychus urticae populations reached higher densities in dimethoate, thiodicarb and methomyl treated cotton than in untreated cotton. Population densities of T. urticae in cotton treated with low rates of endosulfan or thiodicarb were similar to controls, while those in cotton treated with amitraz were lower. All insecticides caused significant reductions in at least one predator group. Significant negative relationships were found between early season abundance of predators and the mid-season abundance of T. urticae and positive relationships between predators and the lag-period for T. urticae outbreaks to develop. Predation is implicated as a key factor influencing the early season survival of T. urticae. The implications for developing integrated pest management strategies in cotton are discussed.