Ecological and evolutionary aspects of photothermal regulation of diapause in trichogrammatidae

Abstract

Facultative winter diapause in the genus of Trichogramma Westw. (Hymenoptera, Trichogrammatidae), like in most other insect species, is regulated by photoperiod and temperature. Their prepupae are diapausing, but sensitivity to temperature and day length (environmental cue factors inducing diapause) is characteristic of all stages of development from embryo to the egglaying female. The environmental cues can affect not only the current, but also the next generations. Under the natural conditions, the photothermal regulation provides the timely diapause induction coordinated both with the astronomical season (the photoperiodic response) and with the peculiarity of the given year (the thermal response). The special experiments revealed "rudimentary responses" that had lost their adaptive role. The results of these studies have proved once more that the specificity of photoperiodic and thermal diapause-regulating responses, their relative importance, and association with sensitive stages of development are determined not only by the ecological peculiarities of different insect taxa, but also by their previous evolution.

Comparative analysis of maternal and grand-maternal photoperiodic responses of Trichogramma species (Hymenoptera: Trichogrammatidae)

“…Direct thermal and maternal photoperiodic effects revealed in our experiments have been demonstrated earlier for the studied species as well as for several other representatives of the genus Trichogramma (Bonnemaison, 1972;Zaslavski & Umarova, 1981, 1990Mai Phu Qui & Zaslavski, 1983;Sorokina & Maslennikova, 1986;Boivin, 1994;Laing & Corrigan, 1995;Garcia et al, 2002;Reznik et al, 2002;Reznik & Kats, 2004;Ma & Chen, 2006;Pizzol & Pintureau, 2008;Sorokina, 2010;Reznik, 2011), although the diapause-inducing effect of a wide range of photoperiods in combination with a range of thermal regimes has been studied only in T. piceum (Reznik et al, 2012b). Similar interaction of direct thermal and maternal photoperiodic responses has been found also in certain other hymenopteran parasitoids from families Aphidiidae (Brodeur & McNeil, 1989;Polgár & Hardie, 2000), Braconidae (Ryan, 1965;Kenis, 1997;Li et al, 2008), and Eulophidae (Milonas & SavopoulouSoultani, 2000).…”

“…However, this reaction is triggered by photoperiod not directly but via the diapause induction (response to short days is blocked in the progeny of aphids which emerged from overwintered eggs). Larval diapause in the blowfly Calliphora vicina R.-D., a very popular insect model for various experimental studies, was shown to be regulated by interaction of direct and maternal responses to the thermal and photoperiodic conditions of the environment (Vinogradova, 1991;Denlinger, 1998Denlinger, , 2002Saunders et al, 2002;Saunders, 2010) and these reactions seem to be very similar to those described for Trichogramma species (Reznik, 2011). Particularly, multigenerational laboratory experiments suggested that direct and maternal photoperiodic responses of C. vicina are based on one and the same physiological mechanism (Bogdanova et al, 1978).…”

“…Theoretically it could be expected that the "threshold zone" of the maternal photoperiodic response is most sensitive to the "grand-maternal correction". This assumption is suggested, for example, by the analogy with the maternal photoperiodic correction of the direct thermal response which in Trichogramma species can be detected only at near-threshold temperatures (Zaslavski & Umarova, 1981, 1990Boivin, 1994;Reznik, 2011). Similarly, the thermal correction of the photoperiodic response is often strongly manifested near the photoperiodic threshold (Tauber et al, 1986;Zaslavski, 1988;Saunders et al, 2002).…”

“…The threshold of the direct thermal response exhibits wide intraspecific variation, but usually temperatures of 10-12°C are optimal for diapause induction, temperatures of 17-20°C and higher stimulate active development independently of day length, while temperatures of 8°C and lower lead to cold quiescence rather than to diapause. The maternal photoperiodic response of Trichogramma species can be usually revealed at temperatures of 13-15°C (Zaslavski & Umarova, 1981, Mai Phu Qui & Zaslavski, 1983Sorokina & Maslennikova, 1986;Zaslavski & Umarova, 1990;Boivin, 1994;Laing & Corrigan, 1995;Garcia et al, 2002;Reznik et al, 2002;Reznik & Kats, 2004;Ma & Chen, 2006;Pizzol & Pintureau, 2008;Sorokina, 2010;Reznik, 2011;Reznik et al, 2011aReznik et al, , b, 2012a. This photoperiodically based maternal modification of the thermal response avoids the untimely induction of diapause in response to occasional cold waves in spring -early summer, when the temperatures of 13-15°C are combined with much longer days than in autumn.…”

“…Finally, at the day of the mass emergence of the maternal generation, a new paper card with 3000-4000 fresh eggs of the grain moth was placed in each tube, subjected to parasitization for 2 h, and separated into 18 small cards (progeny generation) which were randomly distributed among 3 temperature regimes: 13, 14, and 15°C at 12L : 12D and 75% RH. The above temperature regimens were chosen because they are close to the threshold of diapause induction for all the species under study, as suggested by earlier investigations (Zaslavski & Umarova, 1981, Sorokina & Maslennikova, 1986Zaslavski & Umarova, 1990;Reznik et al, 2002;Reznik & Kats, 2004;Reznik, 2011;Reznik et al, 2011a, b) and by our (unpubl.) pilot data.…”