Maternal thermal effect on diapause inTrichogrammaspecies (Hymenoptera: Trichogrammatidae)

Abstract

Both direct thermal and maternal photoperiodic effects on diapause induction have been thoroughly investigated in many insect species, while maternal thermal effects have been infrequently studied. We studied the effect of temperature during development of maternal generation on the proportion of diapausing progeny in four species of the genus Trichogramma Westw., minute egg parasitoids, widely used for biological control of lepidopteran pests. The maternal generations were reared at day lengths of 12 and 18 h and temperatures of 17, 20, 25 and 30°C, and their progeny developed under day length of 12 h and temperatures of 13 and 14°C. In T. evanescens and T. piceum, the proportion of diapausing progeny decreased with increasing temperature under all tested photoperiods and thermal regimes of progeny development; the high temperature of 30°C totally averted diapause of progeny. In T. buesi and T. principium, low temperatures of 17 and 20°C resulted in relatively high proportion of diapausing progeny only when the maternal generation developed under short-day conditions. The threshold of the maternal thermal response varied from 17-18 to 22-23°C. Under field conditions, Trichogramma females are exposed to such high temperatures only during summer, when diapause in their progeny is in any case prevented by the maternal photoperiodic response and by the thermal response of the larvae. We conclude that the maternal thermal effect on diapause induction, although to a different extent, is inherent to Trichogramma species but, at least as suggested by laboratory experiments, it does not play any role in the regulation of seasonal development under natural conditions. However, during mass rearing of Trichogramma wasps, it should be taken into account that high temperature, even when combined with short photoperiod, can avert diapause in the next generation.

How climate change affects the seasonal ecology of insect parasitoids

“…Voinovich et al . () showed that diapause was induced by maternal effects in the parasitoid Trichogramma spp. (Hymenoptera: Trichogrammatidae) when females were reared at a low temperature.…”

“…When environmental cues associated with upcoming deleterious conditions are detected (Danks, 1987;Mousseau & Dingle, 1991), females can adjust the contents of carbohydrates and polyols in the eggs to induce diapause (Denlinger, 2002). Voinovich et al (2015) showed that diapause was induced by maternal effects in the parasitoid Trichogramma spp. (Hymenoptera: Trichogrammatidae) when females were reared at a low temperature.…”

Effects of variable maternal temperature on offspring development and reproduction of Rhopalosiphum padi, a serious global pest of wheat

“…Maternal effects in animals are common and are thought to have a strong ecological and evolutionary significance (Zhou et al, 2013). Previous reports have shown that environmental temperature can mediate maternal effects in insects (Dixon et al, 1982;Voinovich et al, 2015). Heat stress in parental generations affected offspring fitness in Drosophila melanogaster (Gilchrist & Huey, 2001).…”

“…Cold hardiness of offspring was promoted by cold acclimation experienced in the maternal generation of Ophraella communa (Zhou et al, 2013). There was a maternal thermal effect on offspring diapause induction in Trichogramma species (Voinovich et al, 2015). Some life-history traits (development period, longevity and fecundity) were found to be affected by maternal heat stress in the butterfly Bicyclus anynana (Stelgenga & Fischer, 2007) and Aphidius ervi (Ismaeil et al, 2013).…”

Trans-generational effects on diapause and life-history-traits of an aphid parasitoid

“…Powell & Bale (2008) and Coleman et al (2014) demonstrated the existence of adaptive maternal effects on cold hardening in overwintering insects, respectively in the grain aphid Sitobion avenae (Hemiptera: Aphididae) and the blow fly Calliphora vicina (Diptera: Calliphoridae). Among parasitoid insects, Voinovich et al, (2015) showed that diapause was induced by maternal effects in Trichogramma (Hymenoptera: Trichogrammatidae) while it was averted in the offspring when mothers were reared at high temperatures. In some species, there is a non-photo-thermo-sensible generation at which it is impossible to induce diapause, due to maternal effects.…”