Friday, August 7, 2009

PS 92-169: Ecological aspect of generation separation in multivoltine insects in temperate zone

Takehiko Yamanaka, NIAES, William A. Nelson, Queen's University, Koichiro Uchimura, Kagoshima Tea Experiment Station, and Ottar N. Bjornstad, Penn State University.

Background/Question/Methods While many population ecologists had been focusing on the yearly counted data to detect the population regulation, there is another important sign of it; “generation cycle”, in which each generation appears in each separate peak of the population fluctuations. Many mechanisms of the population regulation are proposed to generate such type of cycles as the delay effect, e.g., larval competition for food, asymmetric competition or cannibalism, host-parasitoid interactions with different length of life-cycle and short susceptible period of host and so on. These generation cycles were mainly found in laboratory populations or tropical insect pests where external perturbations can be neglected in some degree. On the other hand, generation cycles of populations in the temperate zone had been regarded as the natural evidence of seasonal enforcement. We picked up an extraordinary detailed tea pest data (Adoxophyes honmai (Lepidoptera: Tortricidae)) collected every 5 days for 44 years, which shows clear from four to five generation cycles per year. Results/Conclusions The periodogram analysis revealed that there are two dominant periodicities in the population dynamics, i.e., the yearly cycle, which is the natural consequence of the seasonality, and one generation period and a bit cycle. A set of delay-differential equations was constructed to explain this cyclic pattern of the insect. The growth rate in each age class in the model is driven by the seasonal temperature fluctuation. External and regular perturbation (a heavy mortality of non-diapausing stages in winter), simultaneous and lumped larval competition, and mate-finding difficulty in adult stage (the Allee effect), are incorporated into the model, respectively. Testing the periodicities of the model outputs, we found that the periodogram pattern was not concordant with the actual data when we only assume the external perturbation, i.e., the winter mortality. Allee effect in adult stage or larval competition together with the external perturbation will be required to explain the cycle of a generation and a bit.

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See more of The 94th ESA Annual Meeting (August 2 -- 7, 2009)