Potato tuber moth Phthorimaea operculella (Zeller) (Lep., Gelechiidae) and tuber infestation in Tunisian potato fields: analysis of the flight phenology
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From 1986 to 1991, pheromone traps were placed in Tunisian potato fields to record weekly the number of male Phthorimaea operculella (Zeller). The data were subjected to a time-series analysis. The coincidence of social events with harvest practices are considered responsible for the relatively high number caught in 1986. In the subsequent years, the pheromone catches gradually decreased, and a linear model was used to remove this trend. A study of seasonality revealed a peak at the beginning of June and another increase in mid-June leading to high catches beyond the period of spring potato crops. After removal of the seasonality the correlogram indicated a stationary stochastic process. By means of a spectral analysis, a four-week cycle, presumably influenced by the moon, and a 10-week cycle, due to unknown causes, were identified. Furthermore, there is an annual cycle related to increasing population densities in spring, i.e. the harvest time of the main-season potato crop.
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