Oviposition pattern and behaviour of the pine sawfly Neodiprion sertifer (Hymenoptera Diprionidae)

The potential role of oviposition deterrents in the egglaying behaviour of Neodiprion sertifer (Geoffroy) females was studied by investigation of natural egg distribution, and by a laboratory study of potential oviposition deterrents. Pine shoots were sampled from different whorls on the sun-exposed and the shaded side of trees. More shoots with eggs from two or more females were found than would be expected if each female laid eggs on a randomly chosen shoot. The anti-predatory larval oral secretion of N. sertifer had no effect on N. sertifer egglaying but acted as an oviposition deterrent to Diprion pini in laboratory experiments. The different responses may be due to differences in the species' life-cycles. In other experiments, the effect of the presence of N. sertifer eggs, extracts obtained from eggs or from needles with eggs, were all tested on N. sertifer egglaying. None of the treatments had any inhibitory effect on egglaying. Thus, neither the natural pattern of egg distribution nor the results of the laboratory experiments indicated that an oviposition deterring pheromone is used by N. sertifer. Results from earlier studies, showing a deterrent effect of larval oral secretion in D. pini, were confirmed.