Oviposition behaviour of Neltumius arizonensis Schaeffer (Coleoptera: Bruchidae) : a biological control agent of Prosopis spp. in South Africa

Master Thesis


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University of Cape Town

Little has been documented on the biology of Neltumius arizonensis Schaeffer. This bruchid is native to the south-western United States of America and is a prospective biological control agent of Prosopis spp. in South Africa. The primary objective of this study was to examine and quantify the oviposition behaviour of N. arizonensis females under different conditions to determine whether eggs of conspecifics or of another bruchid species, Algarobius prosopis (LeConte), affected oviposition. Diet, the number of mates, the duration of access to mates, and the variety of Prosopis pod provided for oviposition all affected the fecundity of N. arizonensis. Optimal conditions for N. arizonensis oviposition included: a diet of pollen pellets in solution, constant access to a limited number of mates, and mature, undamaged Prosopis pods of the 'mottled-purple' variety. The physical structure of the surface of Prosopis pods, observed by scanning electron micrography, did not reveal trends in characteristics among pod varieties that could be linked to the oviposition preferences of N. arizonensis. The rate of oviposition in N. arizonensis peaked between the third and eighth day after emergence from pods and was highest during the first hour when females that had been deprived of pods for at least three days, were provided with pods. Each N. arizonensis female laid an average of about 80 eggs during her lifetime, which was about 3 5 days on average. An event-recording computer programme was developed to quantify the oviposition behaviour of N. arizonensis when females were provided with one of four types of Prosopis pods for one hour: (a) pristine pods, (b) pods with conspecific eggs, (c) pods with A. prosopis eggs deposited within slits, and (d) pods with egg-free slits. Analyses of time budgets indicated that pod type had no significant effect on behaviour, although some activities differed significantly with the type of pod provided, but probably only as a result of the greater number of eggs laid on some pod types. Certain activities i.e. inspection of the pod surface, remaining stationary, and scraping of the ovipositor across the surface prior to egg deposition, occupied significantly more time on pods than other activities. Pod type did not affect the total time females spent on pods, nor the frequency of visits to pods. The availability of clean seeds did not affect the quantity of eggs deposited and the rate of oviposition did not differ significantly on pods of different types.

Bibliography: pages 67-82.