Principal components analysis was used to assess niche partitioning between four aphid predators on the basis of oviposition strategies. The study was conducted by sampling abundance and position of the eggs of these predators in corn monocultures in two locations of southern Quebec. The results indicated that the chrysopid Chrysopa occulata Say laid its eggs on corn leaves usually without aphid colonies, and late in the season. All other predators reacted to aphid concentrations. The syrphid Sphaerophoria philanthus (Mg.) oviposited close to the ground, early in the season, and among colonies of the aphid Rhopalosiphum padi (L.). The two coccinellids laid their eggs during July and August with a maximum during tasseling for Coleomegilla maculata lengi (Timberlake) and after pollination for Hippodamia tredecimpunctata tibialis Say. Of these two species, the latter one selected sites at higher levels on the plant, and was more abundant at the edges of the field. It is suggested that the observed niche partitioning cannot be the result of interspecific competition in variable environments such as maize monocultures.

The recent development of human societies has led to major, rapid, and often inexorable changes in the environment of most animal species. Over the last decades, a growing number of studies formulated predictions on the modalities of animal adaptation to novel or changing environments, questioning how and at what speed animals should adapt to such changes, discussing the levels of risks imposed by changes in the mean and/or variance of temperatures on animal performance, and exploring the underlying roles of phenotypic plasticity and genetic inheritance. These fundamental predictions, however, remain poorly tested using field data. Here, we tested these predictions using a unique continental‐scale data set in the European earwig Forficula auricularia L., a univoltine insect introduced in North America one century ago. We conducted a common garden experiment, in which we measured 13 life‐history traits in 4,158 field‐sampled earwigs originating from 19 populations across North America. Our results first demonstrate that 10 of the 13 measured life‐history traits are associated with two sets of variations in seasonal temperatures, that is, winter–summer and autumn–spring. We found, however, no association with the overall mean monthly temperatures of the invaded locations. Furthermore, our use of a common garden setup reveals that the observed patterns of variation in earwigs’ life‐history traits are not mere plastic responses to their current environment, but are either due to their genetic background and/or to the environmental conditions they experienced during early life development. Overall, these findings provide continent‐scale support to the claims that adaptation to thermal changes can occur quickly (in less than 100 generations), even in insects with long life cycles, and emphasize the importance of variation in seasonal temperature over mean population temperatures in climate adaptation.

We studied the effects of frost on the survival rate of European earwigs, Forficula auricularia L., during the underground phase of their cycle and determined the timing of oviposition, hatching, and death of the adults; we selected couples and inserted them into the ground to a depth of 150 cm in an open area and along the foundations of a heated suburban house in the Montréal area. Oviposition occurred in November and December, and eggs hatched between January and early June, after an average incubation period of 79–189 d depending on experimental conditions. In the open area all adults and eggs at ground surface died, killed by frost, whereas those in the soil along the house foundation did not die. Males died during the fall and early winter; their longevity was shorter than that of females, which survived until shortly after egg hatch. Females and eggs survived temperatures as low as − 3 and − 2 °C, respectively. For successful reproduction, females must keep their developing eggs at a temperature low enough to delay hatching until mid-April.

Egg-laying patterns of the European earwig, Forficula auricularia Linnaeus (Dermaptera: Forficulidae), from three climatologically different areas; Montréal, Québec, Canada, Vancouver, British Columbia, Canada, and San Francisco, California, United States of America; were compared in laboratory. Three different egg-laying patterns were observed. Among the biotic parameters studied; previtellogenic follicular atresia, number of oocytes per ovariole at imaginal moult, female life expectancy, and ovarian activity explained female successful responses to local weather conditions. Follicular atresia, combined with a low number of oocytes, impeded oviposition in a low percentage of females from Montréal. It also impedes the production of a third brood in the Vancouver population, and of a fourth brood in the San Francisco population. Both female life expectancy and length of ovarian activity also had a significant impact on the oviposition pattern in the three climatic regions. Under the cold temperate climate of the Montréal area, only one brood was produced due to the short period of female fertility. Longer period of fertility and life expectancy enabled females to produce two broods in the milder temperate climate of Vancouver, and three broods in the San Francisco climate. Our results strongly suggest an exaptation enabling the native European populations of F. auricularia to adapt successfully in North America.

The egg laying regime of Forficula auricularia L., defined by different parameters (number of broods, proportion of females that produce two broods, number of eggs produced at each batch, and the proportion of the total number of eggs represented by the first batch), was studied in the laboratory and under seminatural conditions for a population from Montréal. Approximately half of the females produced two batches of eggs in the laboratory; however the number of eggs produced in the first batch was substantially higher than that of the second batch. In the field a single batch of eggs was produced. Comparison of our data with the literature showed that the Montréal population appears to have a greater resemblance to one of a cold temperate climate (Font-Romeu, Eastern Pyrénées) than one of a warmer climate (Rennes, Bretagne) for all parameters studied.