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Diapause, seasonal physiological dormancy, is the primary life history strategy used by insect species inhabiting temperate climates for seasonal synchronisation. Biotic signals for diapause induction originating from host plants may provide dependable cues for insects expanding from subtropical regions., We investigated the effect of plant-mediated photoperiod cues on diapause initiation within the Colorado potato beetle, Leptinotarsa decemlineata Say. The effect of photoperiod changes on potato leaf composition and its subsequent correlation with diapause initiation was tested., Analyses revealed a significant effect of short-day ( LD 8 : 16 h and LD 10 : 14 h) photoperiod growth regimens on both nitrogen content in potato leaves and diapause initiation within L. decemlineata., Potato plants grown under short day conditions displayed significantly higher levels of leaf nitrogen compared with long-day treated plants. Over 65% of beetles feeding upon short-day treated plants initiated diapause compared with < 20% of beetles placed upon long-day treated plants., The observation of seasonality-induced diapause signals by host plants signifies an important addition to the current array of plant-insect interactions. The present results suggest that seasonal synchrony may be the result of a more integrated system whereby host plant photoperiodism acts as an intermediate or supplementary physiological cue for diapause initiation. [ABSTRACT FROM AUTHOR]

Dormancy and dispersal are thought to be major adaptive mechanisms that enable short-lived organisms to cope with environmental stochasticity. The few empirical investigations that have explored the relationship between these two strategies in disturbed environments have focused mainly on communities of annual desert plants and suggest that dispersal plays a negligible role, as compared with dormancy, in reducing the risk of genotype extinction., We predict that the relative advantage of dormancy versus dispersal is likely to be more balanced in species that disperse actively to select their reproductive locality., To examine this prediction, we explored the dormancy and dispersal capacities of four actively dispersing sibling weevil species ( Curculio spp.) that exploit the same, highly variable resource (oak acorns). The ability of each species to spread risks over time was estimated from the variability of dormancy duration within cohorts, while their ability to disperse spatially was quantified by flight performance., We show that a first species, C. elephas, which was able to spread risk over time through dormancy, exhibited only medium flight capacities. In contrast, a second species, C. glandium, was able to fly over very long distances, but was hardly capable of spreading risk over time. Surprisingly, the two remaining species ( C. venosus and C. pellitus) proved inefficient in spreading risk either in space or in time and seem to exhibit risk avoidance rather than risk-spreading strategy. We conclude that this strong diversification of dispersal-dormancy strategies observed among these four sibling species might contribute to stabilising their coexistence. [ABSTRACT FROM AUTHOR]

1. Some insects have a prolonged diapause - a dormancy that extends over more than 1 year. In most species prolonged diapause involves one or a few extra years, but in extreme cases diapause may surpass 10 years. Few cases of very long diapause have been described, and very little is known about the population consequences of the temporal refuge formed by the diapausing individuals. 2. The gall midge Contarinia vincetoxici Kieffer galls the flowers of a long-lived herb Vincetoxicum hirundinaria Med. After completing development, larvae leave the galls for the ground where they enter diapause. Extending an earlier published inoculation experiment, we show that the diapause may last up to at least 13 years, with a median duration of at least 6 years. 3. The gall midge is attacked by two parasitoid species. Dissections of gall midge larvae for presence of parasitoids revealed that Omphale salicis Haliday had a maximum 2 year diapause and Synopeas acuminatus Kieffer a maximum 4 years. The very long diapause of the gall midge may thus provide a temporal refuge from these enemies. 4. In a 15-year field experiment all galls were removed every year from six isolated habitat patches. Density changes in experimental populations were not statistically different from control populations for over a decade. After 14-15 years a modest decline could be observed. This slow response illustrates that prolonged diapause in C. vincetoxici provides a very strong population buffer against mortality during the galling stage. [ABSTRACT FROM AUTHOR]