Diapause induction in the codling moth, Cydia pomonella: effect of prediapause temperatures

The effect of four prediapause temperatures (18, 22, 26 and 30°C) on the photoperiodic response of the codling moth, Cydia pomonella (L.), was studied under controlled conditions. The highest rates of diapause were recorded, for all day-lengths, at temperatures of 22 and 26°C while relatively lower rates of diapause were elicited at 18 and 30°C. The same trend was demonstrated by projecting the values of the critical photoperiod which induces 50% diapause (=CPhP₅₀) over the prediapause temperature. The change in diapause incidence as a function of photoperiod, at all prediapause temperatures, exhibited a response characteristic of long-day insects, i.e. high rates of diapause at short days (12–13.5 h) and a decrease in diapause incidence at long days (14–15 h). The results for temperatures 22, 26 and 30°C support the view that lower prediapause temperatures enhance diapause induction, at a give photoperiod, while higher temperatures tend to avert or diminish the process. On the other hand, the low rates of diapause obtained at 18°C contradict this view. Nevertheless, high correlation was found between the laboratory evidence and field data, indicating the adaptability of the Israeli codling moth to subtropical climate.