Biology of subterranean populations of woolly apple aphid, Eriosoma lanigerum (Hausmann)(Homoptera:Aphididae), in apple orchards
[摘要] ENGLISH ABSTRACT:A study was made of the basic biology of subterranean Eriosomalanigerum (Hausmann) populations in apple orchards in the Western CapeProvince of South Africa.The absence of cornicles and the presence of a vulva could be used toidentify 1st instar nymphs and adults respectively. Body length, body width andlength of the hind femur are useful for separating 2nd, 3rd and 4th instars.However, separation of 2nd from 3rd instar nymphs was very unreliable.Maximum population growth rate was at 23°C while at 30 °Cpopulation growth was zero. The estimated minimum and maximum thresholdtemperatures for development were 4.32 and more than 30°C respectively.Numbers of underground E. lanigerum in soil samples taken usingmechanical and hand augers were similar. However, numbers of aphids insamples were influenced by the distance from the trunk at which the sampleswere taken and the presence and the type of root material in the samples.More aphids were recorded close to the trunk, and at a given distance fromthe trunk more aphids were recorded if there was root material in the sample,especially if the roots were galled. early autumn (February, March) and declined during winter, especially if thewinter rainfall was high. These cycles coincided with the nitrogen cycles in theroots.Embryos were also present in all instars throughout the year. Therewere more embryos in the 4th instar and adult aphids than in the other instars.The highest number of embryos in the 4th instar and adult aphids occurredduring spring, which coincided with peak nitrogen levels in the roots of appletrees. Nitrogen levels in root material adjacent to galls and in ungalled rootswere higher than in root galls.A number of entomopathogenic fungi, including species ofConidiobolus, Hirsufella and Beauveria were found. Their present contributionto biological control is not known.A straw mulch suppressed subterranean E. lanigerum population levelsat least as well as the soil insecticide, imidacloprid, currently in use.
[发布日期] [发布机构] Stellenbosch University
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