Laboratory-based experiments are presented involving two aphid sepcies (Myzus persicae Sulzer, a generalist and Brevicoryne brassicae Linnaeus, a crucifer specialist), and the predatory gall midge, Aphidoletes aphidimyza Rondani, on three cultivars of common cabbage Brassica oleracea var. capitata cv. Derby Day (green-leaved), Minicole (green-leaved) and Ruby Ball (red-leaved). In a laboratory-based tritrophic system including both species of aphid, the three cabbage cultivars and A. aphidimyza, predator both species of aphid, the three feeding on M. persicae or B. brassicae on cv. Derby Day, while growth was slowest separate experiment, A. asphidimyza larva feeding on B. brassicae on each of the three cultivars were significantly smaller and consumed less aphid fresh weight when maintained outdoors (mean temperature = 13.5°C) compared with a constant environment room (20°C). However, in this latter experiment under neither regime were differeneces in predator growth or consumption significant between cultivars. Effects of selective insecticides (pirimicarb and a neem seed kernel extract, NeemAzal-T/SR) on bitrophic (aphid-host plant) interactions were also investigated in the laboratory. A pirimicarb dose equating to c. 15% of the recommended field concentration caused equivalent toxicity of M. persicae on cv. Minicole compared with aphids treated with a three-fold greater dose and reared on cv. Derby Day. Cultivar-mediated differences in aphid mortality caused by the neem extract when tested for systemic and translaminar activity were not apparent. The results are discussed in relation to ways in which host plant selection, selective insecticides and biological control could potentially be manipulated and optimized in aphid management system on brassica crops.

Details of the life history, the effects of relative humidity and temperature on survival and reproduction, and the predatory ability of Aleurodothrips fasciapennis Franklin were examined under laboratory conditions. Stage-specific development and adult longevity were similar between sexes, and the adult sex ratio was 1:1. Females laid 23.3 ± 18.0 eggs of which 83% hatched. The survival rate of first instars to adulthood was 82%. The intrinsic rate of natural increase (rm) was 0.04, assuming a zero or 5.4 day pre-oviposition interval. Temperature did not affect the proportion of eggs that hatched, the proportion of first instars surviving to adulthood or adult sex ratios. However, female fecundity was dependent on temperature being highest at 24 ndash 28°C. Relative humidity did not affect adult sex ratio or female fecundity but the proportion of eggs hatched and the survival of first instars to adulthood increased as relative humidity increased. Few eggs hatched when relative humidity was <65%. Larval and adult female A. fasciapennis were voracious feeders but the number of prey killed per progeny was high, suggesting A. fasciapennis was inefficient at converting prey into progeny biomass. The potential value of A. fasciapennis as a biocontrol agent of Aonidiella aurantii (Maskell) on Australian citrus is discussed in terms of its rm, prey killing power and environmental adaptability. It is concluded that population growth of A. fasciapennis should exceed that of A. aurantii under field conditions but A. fasciapennis may be of little value against A. aurantii on citrus grown under conditions of high temperature and low humidity, or when prey densities are low.

Brightwell, R., Dransfield, R. D., Stevenson, P. and Williams, B. Changes over twelve years in populations of Glossina pallidipes and Glossina longipennis (Diptera: Glossinidae) subject to varying trapping pressure at Nguruman, south-west Kenya.

The correct mailing address for the authors is SNV Kenya, Ngong Lane, P.O. Box 30776, Nairobi, Kenya.