Effects of five weed management regimes on abundance of weeds, insect pests, generalist predators and on pest damage and rice yield were investigated in upland rice in Côte d‘Ivoire over two years. In both years there was a highly significant negative correlation between weed biomass and grain yield across all treatments. Only two pest insect groups, Nephotettix spp. (Cicadellidae) and seed sucking Heteroptera, were consistently more abundant in unweeded plots and had a consistent significant positive correlation between abundance and weed biomass across all seven treatments. These polyphagous groups may have been more dependent on resources provided by weeds than the other pests studied. However, pest damage was not affected by presence or absence of weeds, suggesting that populations were below a damage threshold. Ants were the most abundant predators in the rice canopy and were most abundant in unweeded treatments. Abundance of both ants and spiders was significantly positively correlated with weed biomass across treatments. Abundance of reduviid bugs was positively correlated with weed biomass only in 1995. Any benefits due to presence of weeds in the crop were completely outweighed by loss of crop yield due to weed competition. However, if crop losses due to weeds were sufficiently reduced, it is possible that significant losses due to insect pests might emerge.

The mealybug Phenacoccus herreni Cox & Williams causes considerable damage to cassava Manihot esculenta Crantz. Field surveys conducted between 1988 and 1994 indicated the mealybug was present in 57 municipalities in six States in north-eastern Brazil, in some places reaching high levels of infestation. Several native natural enemy species were found associated with the pest in Brazil. Exotic encyrtid parasitoids were imported and released in fields in the States of Bahia and Pernambuco. Apoanagyrus diversicornis (Howard) was introduced from Colombia, and Acerophagus coccois Smith, and Aenasius vexans (Kerrich) were introduced from Venezuela. By the end of 1996, a total of 35,930 parasitoids had been released. In Bahia, Apoanagyrus diversicornis was recovered 130, 234, 304 and 550 km from its release site after 6, 14, 21 and 33 months, respectively. Acerophagus coccois was recovered at 180 km from its release site nine months after release. Aenasius vexans, however, did not disperse at all despite being consistently recovered at its release site. In Pernambuco, 9010 parasitoids were released from October, 1995 onwards. Acerophagus coccois and Aenasius vexans were recovered up to 40 km from the release sites after three and five months of their initial releases, respectively. The establishment and dispersal of these parasitoids are discussed.

Populations of rice leaffolders and their natural enemies were studied in eight crops of irrigated rice in Laguna Province, the Philippines. The rice leaffolder complex consisted of three species: Cnaphalocrocis medinalis (Guenée), Marasmia patnalis Bradley and M. exigua Butler. Leaffolder population dynamics were characterized by an egg peak at maximum tillering and a broad larval peak around booting stage. Peak densities ranged from 0.2 to 2.0 larvae per hill. Most larvae originated from immigrant moths and there was no substantial second generation. The seasonal percentage egg parasitism by Trichogramma sp. ranged from 0 to 27%, and percentage larval parasitism from 14 to 56%. The braconid Macrocentrus philippinensis Ashmead was the most commonly reared larval parasitoid. Forty natural enemy taxa that may attack rice leaffolders were identified from suction and sweepnet samples: 24 predator taxa and 16 parasitoid taxa. The estimated survival rates from leaffolder egg to larval stages and between larval stages showed large variation between rice crops, but were not clearly correlated with observed levels of parasitism, natural enemy abundance, or natural enemy to leaffolder ratios. It is suggested that the generally low densities of rice leaffolders in Philippine transplanted rice are caused by their ovipositional preference for crops at the maximum tillering stage, allowing for only one generation, and by high immature mortality caused by the abundant and diverse complex of natural enemies.

Flight by Listronotus bonariensis (Kuschel) in Canterbury, New Zealand varied greatly both within and between seasons; no winter flight was detected between mid-May and mid-August. Predisposing conditions for flight were found to be >19degC, rh <81% and windspeed <10.8 km h–1. Three flight phases with different characteristics were identified when approximately equal numbers of weevils were trapped. These were between mid-August and early December (overwintered weevils), between early December and mid-March (first summer generation weevils) and mid-March and mid-May (first and second generation weevils). The proportion of individuals with developed flight musculature was c. 8% in the first phase and 30% in the last phase; muscle development was delayed in the mid-phase. First phase weevils with flight muscles were c. 20 times more likely to fly than those in the last. A very weak inverse relationship was observed between developed flight musculature and the presence or absence of eggs. Similarly, there was a very weak inverse relationship between weevil ground densities and the proportion with developed flight muscles. Levels of parasitism by Microctonus hyperodae Loan amongst trapped weevils were far less than that on the ground, indicating that it inhibits flight and may explain the relatively slow dispersal of the parasitoid. It was concluded that the adaptive implications of flight could be linked to escape responses from desiccating microclimates rather than dispersal from crowded habitats.

The influence of protein in the adult diet on first cycle gonotrophic development was examined in newly colonized screwworm flies, Cochliomyia hominivorax (Coquerel), reared on an artificial larval diet and bred in subsequent generations from females stimulated to oviposit only after all individuals in a colony were expected to have matured their eggs. This latter criterion was established with the goal of reducing selection for early ovarian maturity and increased autogeny. Under these conditions, supplementing the diet with raw meat during the first week after adult emergence hastened egg maturation by two to four days or more, increased the percentage of seven- to ten-day-old females that was gravid by 45%, and boosted the number of eggs per gravid female by c. 30%. The serous discharge from screwworm-infested sheep wounds, a casein–salt mixture, or casein in potassium hydroxide was as effective as raw meat. Addition of B vitamins to the casein–salt mixture was without further effect. The measures taken to reduce selection for altered gonotrophic development were not critically evaluated here, but they appeared successful in that age and protein affected ovarian maturation rates similarly in F2 and F27. Fecundity measured as eggs matured per gravid female differed between generations, but appeared correlated with size differences that were unrelated to colonization duration.

Field sampling of grasses growing in and near rice fields at 12 sites in Nigeria during April/May 1994 recorded the presence of galls on Paspalum scrobiculatumat densities of up to 10.9 galls per m2. These galls were induced by Orseolia bonzii Harris, sp. n., which is described. This species is morphologically close to, but distinct from, the African rice gall midge, Orseolia oryzivora Harris & Gagné, with which it has been confused in earlier studies of that pest species. In host-transfer experiments O. bonzii did not transfer to rice, Oryza sativa. Six hymenopterous parasitoids were reared from galls of O. bonzii and the most abundant of these were Platygaster diplosisae Risbec, Aprostocetus nr. procerae (Risbec) and Neanastatusnr. cinctiventris Girault. Host-transfer experiments with the Platygasterand Aprostocetus species from O. bonzii on Paspalum indicated that the Platygaster may not transfer onto O. oryzivora on rice whereas the Aprostocetus does. The overlap between the parasitoid faunas of the two species of Orseolia is potentially useful as it may be possible to enhance the natural biological control of O. oryzivora by manipulating parasitoid populations on Paspalum.

Realized heritability, h2, of resistance in European corn borer, Ostrinia nubilalis (Hübner), to Bacillus thuringiensisBerliner ssp. kurstaki endotoxins was examined in five resistant laboratory colonies. These colonies were reared on a meridic diet that incorporated a commercial formulation of B. thuringiensis, Dipel ES. Resistance in these colonies reached 42–67× by the seventh to twentieth selected generations and then plateaued. The realized heritability of resistance averaged 0.17–0.31 over all selected generations for the five colonies. In the three Iowa colonies, the highest realized heritability, 0.18–0.33, occurred during the second period of selection (seventh to thirteenth selected generations). In the two Kansas colonies, the highest realized heritability, 0.36 and 0.46, occurred during the first period of selection (first to sixth selected generations). In the absence of selection pressure, resistance in the southwest Kansas colony decreased from 62× to 42× after two generations, and remained at about that level for the next five generations.

Regression analyses of a long series of light-trap catches at Narrabri, Australia, were used to describe the seasonal dynamics of Helicoverpa armigera (Hübner). The size of the second generation was significantly related to the size of the first generation, to winter rainfall, which had a positive effect, and to spring rainfall which had a negative effect. These variables accounted for up to 96% of the variation in size of the second generation from year to year. Rainfall and crop hosts were also important for the size of the third generation. The area and tonnage of many potential host crops were significantly correlated with winter rain. When winter rain was omitted from the analysis, the sizes of both the second and third generations could be expressed as a function of the size of the previous generation and of the areas planted to lucerne, sorghum and maize. Lucerne and maize always had positive coefficients and sorghum a negative one. We extended our analysis to catches of H. punctigera (Wallengren), which declines in abundance after the second generation. Winter rain had a positive effect on the sizes of the second and third generations, and rain in spring or early summer had a negative effect. Only the area grown to lucerne had a positive effect on abundance. Forecasts of pest levels from a few months to a few weeks in advance are discussed, along with the improved understanding of the seasonal dynamics of both species and the significance of crops in the management of insecticide resistance for H. armigera.

Life table studies of Mussidia nigrivenella Ragonot, a pest of maize in Benin, showed that host plant species had a significant effect on larval survival and developmental time. The maximum percentage of larvae surviving was recorded on jackbean, Canavalia ensiformis (36%) and lowest on maize (18%). Mean developmental time for larvae was longest on maize (19.8 days) and shortest on jackbean (17.2 days). The number of eggs laid was highest for females from larvae fed on jackbean (x– = 176), followed by velvetbean, Mucuna pruriens(x– = 143), and lowest for females where larvae had fed on maize (x–= 127). Longevity of ovipositing females was higher on jackbean (5.4 days) than of those from any other host plants. According to the growth index and life table statistics, jackbean was the most suitable host plant, followed by velvetbean, and maize, the least suitable. Thus, jackbeans should be recommended for use in mass rearing programmes of M.nigrivenella, e.g. as a host for parasitoids in future biological control programmes. Because of the high suitability of jack- and velvetbeans for M.nigrivenella, planting of these increasingly important cover crops should be timed in such a manner that the emergence of female moths from mature pods does not coincide with maize plants in a suitable developmental stage for oviposition and development of young M. nigrivenella larvae.

Nineteen sites throughout Ghana were selected as representative of the three major zones of natural vegetation. At these sites, samples of ticks were collected from groups of approximately five each of cattle, sheep and goats. Ticks were identified by light microscopy. In order of abundance, tick species found on livestock were: Amblyomma variegatum (Fabricius), Boophilus decoloratus (Koch), Rhipicephalus senegalensis Koch, Boophilus annulatus (Say), Hyalomma marginatum rufipesKoch, a Rhipicephalus species in the sanguineus group of uncertain identity close to both R. turanicus Pomerantsev and R. sulcatus Neumann, Boophilus geigyi Aeschlimann & Morel, Hyalomma truncatum Koch, Rhipicephalus evertsi evertsi Neumann and Rhipicephalus lunulatus Neumann. Amblyomma variegatum was found on every sample of the sheep, goats and cattle examined and was equally abundant in all vegetation zones. Boophilus species were found mainly on cattle, with some on sheep and were widely distributed by vegetation zone. Hyalomma species were found predominantly on cattle and widely distributed by vegetation zone. Rhipicephalus e. evertsi and R. senegalensis were found on sheep and cattle in all vegetation zones. The tick fauna of Ghana is similar to those of other West African countries and this shows that control strategies developed in neighbouring countries can be applied to Ghana. The significance of this tick fauna is discussed in relation to potential for pathogen transmission.