Occurrence of two different development patterns in Lobesia botrana (Lepidoptera: Tortricidae) larvae during the second generation

In north-eastern Italy, the second-generation larvae of Lobesia botrana (Den. & Schiff.) (Lepidoptera: Tortricidae) can develop with two different time patterns. In particular, in warmer' areas, the developmental time is shorter than in cooler' areas and it is associated with an earlier and more economically important third generation. Because the differences in temperature are not sufficient to explain the two patterns, research was carried out aiming to investigate whether the differences in larval development time are the result of a different number of instars and whether the photoperiod is a factor. In the field, second-generation larvae develop through five instars in a warmer' area and through six instars in a cooler' area. Laboratory and field data showed that decreasing photoperiod, which induces diapause, is also an important cue for inducing larvae to develop six instars. In the light of climate warming and subsequent changes in L. botrana phenology over the last 30years, the two different development patterns are interpreted as a means to ensure the best fit of the moth to environmental conditions. In cooler' areas, third-generation larvae might not complete development before frost or harvest, and hence second-generation larvae develop through six instars before producing overwintering pupae.