The effect of winter length on duration of dormancy and survival of specialized herbivorous Rhagoletis fruit flies from high elevation environments with acyclic climatic variability

Abstract

Dormancy can be defined as a state of suppressed development allowing insects to cope with adverse conditions and plant phenology. Among specialized herbivorous insects exploiting seasonal resources, diapause frequently evolves as a strategy to adjust to predictable plant seasonal cycles. To cope with acyclic and unpredictable climatic events, it has been found for some insects that a proportion of the population undergoes prolonged dormancy. We compared the response of three species in the Rhagoletis cingulata species group exploiting plants differing in fruiting phenology from environments varying in frequency and timing of acyclic climatic catastrophic events (frost during flowering and fruit set) and varying also in the time of the onset of the rainy season. Small proportions (<2%) of Central and Northeastern Mexico R. cingulata and Rhagoletis turpiniae, and a few associated adult parasitoids, emerged without becoming dormant. Pupae exposed to 5°C for different periods of time (0–16 weeks) became dormant and emerged as adults in proportions <30%, compared with other studied species in the group from the USA (up to 80%). Large proportions (19–55%) of exposed pupae entered prolonged dormancy (>10 months), and large proportions of pupae died without emerging as adults. The number of days elapsed from the end of artificial winter and adult eclosion was longer for R. cingulata exploiting late fruiting Prunus serotina in Northeastern Mexico than for flies recovered from earlier fruiting plants in the central Altiplano. Rhagoletis turpiniae and northeastern R. cingulata pupae suffered high proportions of parasitism. Large proportions of R. cingulata from central Mexico engaging in prolonged dormancy may be explained by the fact that flowering and fruit set for its host, P. serotina var capuli, driven by the timing of maximum precipitation, matches a period of highest probability of frost often resulting in large areas with fruitless trees at unpredictable time intervals. As a consequence of differences in host plant fruiting phenology, central and northeastern Mexican R. cingulata were found to be allochronically isolated. Prolonged dormancy may have resulted in escape from parasitism.