Are aphid parasitoids from mild winter climates losing their winter diapause?

Abstract

Temperature is both a selective pressure and a modulator of the diapause expression in insects from temperate regions. Thus, with climate warming, an alteration of the response to seasonal changes is expected, either through genetic adaptations to novel climatic conditions or phenotypic plasticity. Since the 1980s in western France, the winter guild of aphid parasitoids (Hymenoptera: Braconidae) in cereal fields has been made up of two species: Aphidius rhopalosiphi and Aphidius matricariae. The recent activity of two other species, Aphidius avenae and Aphidius ervi, during the winter months suggests that a modification of aphid parasitoid overwintering strategies has taken place within the guild. In this study, we first performed a field survey in the winter of 2014/15 to assess levels of parasitoid diapause incidence in agrosystems. Then, we compared the capacity of the four parasitoid species to enter winter diapause under nine different photoperiods and temperature conditions in the laboratory. As predicted, historically winter-active species (A. rhopalosiphi and A. matricariae) never entered diapause, whereas the species more recently active during winter (A. avenae and A. ervi) did enter diapause but at a low proportion (maximum of 13.4 and 11.2%, respectively). These results suggest rapid shifts over the last three decades in the overwintering strategies of aphid parasitoids in Western France, probably due to climate warming. This implies that diapause can be replaced by active adult overwintering, with potential consequences for species interactions, insect community composition, ecosystem functioning, and natural pest control.

Day length constrains the time budget of aphid predators

“…Novel day length – temperature correlations can make the timing of diapause maladaptive (Yee et al ., ; Chen et al ., ), and thus pose a short‐term constraint on phenology shifts. The timing of diapause has however been shown to be responsive to selective pressures (Urbanski et al ., ), and diapause may even be given up entirely if winters are permissive (Tougeron et al ., ). We hence find it unlikely that these constraints persist on the long term.…”

Intraspecific maternal competition induces summer diapause in insect parasitoids

“…Aphidius avenae and Aphidius rhopalosiphi were collected from cereal fields in Western France (Long Term Ecological Research area ZA Armorique , 48°08′N, 1°80′W) in 2014 and 2015 (details in Tougeron et al ., ) and have since been reared on a colony of the grain aphid S. avenae established from a single female collected at Le Rheu, France, in 1990. Parasitoids were reared at 20 °C, 70% relative humidity (RH), and under 16 h : 8 h light : dark (L : D) photoperiod while aphids were reared at 24 °C, 55% RH, and 16 h : 8 h L : D on winter wheat ( Triticum aestivum var.…”

Diapause research in insects: historical review and recent work perspectives

“…Indeed, climate warming is expected to lead to more important pest outbreaks (Björkman & Niemelä, ) and the longer growing period generated by rising temperatures may lead to presence of crop pests throughout winter, as it has already been documented for some aphid species (Dedryver et al., ). Among parasitoids, temperature has a strong impact on diapause expression (Li et al., ; Tougeron et al., ) but also on host‐parasitoid interactions, such as parasitoid attack rates and virulence, host defensive behavior, and immune responses (Cayetano & Vorburger, ; Le Lann et al., ; Delava et al., ; Wu et al., ). Thus, potential modifications in overwintering strategies, either of the pests or their natural enemies, can destabilize food webs and modify (positively or negatively) the efficiency of biological control (Thomson et al., ; Furlong & Zalucki, ).…”

“…Photoperiod will not be modified by climate change at a given latitude, but temperature will, thus modifying environmental pressures that maintain diapause expression within insect populations. This could lead to rapid plastic or evolutionary (genetic) responses of insect photoperiodism and phenology to adapt to new seasonal conditions (Bale & Hayward, 2010;Tougeron et al, 2017).…”