Showing papers by "Wilf Powell published in 1993"

Management of Genetics of Biological-Control Introductions

Abstract: For over 100 years, arthropod pests and weeds have been controlled by the introducion of exotic natural enemies (21). For almost as long, entomologists have discussed the importance of genetics and the possibility of genetic manipulations in biological control, and today these remain subjects of considerable debate. Perhaps the first issue raised was that predators and parasites might be artificially selected for improved performance in the field (46, 47, 59). In contrast, a major concern for laboratory rearing of insects and mites used in biological control is that such rearing will promote genetic adaptation to laboratory conditions and thus worsen performance in the field (57. 58). Another concern is that natural enemies imported for biological control constitute only a limited sample of the genetic variation present in the species, and may therefore lack the ability to adapt to their new environment (64,65). Many of these issues. and possible solutions. have been discussed recently

The relationship between primary parasitoids and hyperparasitoids of cereal aphids: an analysis of field data

Abstract: 1. We analysed data collected in 1985-89 from cereal fields to elucidate the relationships between the primary parasitoids and hyperparasitoids of cereal aphids. The analysis aimed to establish whether or not hyperparasitoids interfere with the impact of primary parasitoids on cereal aphid populations. 2. From more than 10000 parasitized aphids, 14 primary parasitoid and 18 hyperparasitoid species were reared. The five most common hyperparasitoids attacked the five most common primary parasitoids, which, in turn, parasitized most frequently the most abundant aphid species, Sitobion avenae (F.). 3. Levels of aphid primary parasitism never exceeded 33%, whereas levels of hyperparasitism often reached 100% in the latter part of the season. However, the low rates of aphid primary parasitism could not have been solely the result of hyperparasitism: if primary parasitoid females which emerged early continued to deposit eggs before the collapse of the aphid populations, those females should have been numerous enough to parasitize large numbers of their hosts before hyperparasitoid pressure became high. 4. We hypothesize that primary parasitoid females leave areas which develop high hyperparasitoid densities. A multiple linear regression model was used to test the hypothesis. The observed declines of aphid primary parasitism were quantitatively related to hyperparasitoid density. 5. The results of this study and additional theoretical considerations are in favour of the above hypothesis. However, other factors such as mortality other than that due to hyperparasitoid attack, and aestivation acting together may also contribute to the low abundance of primary parasitoid females later in the season.

Responses of the parasitoid Praon volucre (Hymenoptera: Braconidae) to aphid sex pheromone lures in cereal fields in autumn: Implications for parasitoid manipulation

Abstract: Females of the aphid parasitoid Praon volucre were attracted to lures containing synthetic aphid sex pheromone components, particularly (+)-(4aS,7S,7aR)-nepetalactone, when these were placed on water traps in cereal fields in autumn. Trap catches were greatest at a site in S.W.England and fewest at sites in northern England 'and northern Germany, presumably due to climatic differences. Responses to the pheromones were not detected for any other cereal aphid parasitoids in the field trials, although Aphidius rhopalosiphi appears to possess olfactory receptors for (+)-(4aS,7S,7aR)-nepetalactone. A potential strategy for the use of aphid sex pheromone lures to manipulate aphid parasitoids in the field, in order to enhance their impact on aphid populations, is outlined.

Sex pheromones in the cereal aphid parasitoids Praon volucre and Aphidius rhopalosiphi

Abstract: Laboratory and field experiments provided evidence for the release of sex pheromones by virgin female Praon volucre Haliday and Aphidius rhopalosiphi De Stefani-Perez (Hymenoptera: Braconidae, Aphidiinae). In Petri dish biosassays, rubber or vermiculite models treated with crude virgin female extracts were frequently approached by males and elicited rapid wing-fanning behaviour and copulation attempts. Delta-shaped water traps containing live virgin females caught large numbers of conspecific males when placed in winter wheat crops. Trapping slightly below crop height resulted in higher catches than trapping above the crop canopy.