Arrhythmic adult ecdysis but rhythmic emergence from the host chorion in Trichogramma embryophagum (Hymenoptera: Trichogrammatidae)

Abstract

Abstract. In many insect species with a pupa covered by various "shells" (puparium, host remains, etc.) pupal-adult ecdysis and emergence to the open air represent two discrete steps. However, in Trichogramma, as well as in other insect parasitoids, these two processes have never been studied separately. We investigated the temporal pattern of pupal-adult ecdysis and of adult emergence from the host chorion in Trichogramma embryophagum Hartig (Hymenoptera: Trichogrammatidae) in laboratory conditions (12L : 12D, 20°C). Adult ecdysis was arrhythmic, while adult emergence showed a strong rhythmicity. The time lag between ecdysis and emergence varied from one to almost two days, depending on the circadian time of the ecdysis. The proportion of ecdysed adults that stayed in the host chorion ranged up to 60% (just before the highest peak of emergence). The cumulative percentage of ecdysed adults gradually increased with time, independently of whether the light was turned on in accordance with the entrained circadian rhythm or 4 h earlier. This arrhythmic ecdysis could be explained by the fact that the ecdysed adults get into a well protected space inside the host chorion and the timing of this event is adaptively neutral.

Circadian rhythms of adult emergence and activity but not eclosion in males of the parasitic wasp Nasonia vitripennis

“…Contrary to what is observed in activity rhythms, emergence does show anticipation towards the darkness-light transition, which can be an additional indication of the action of an underlying clock. Anticipation of eclosion is also observed in D. melanogaster (Qiu and Hardin, 1996) but not in T. embryophagum where emergence from the host chorion is rhythmic but does not show anticipation (Reznik et al, 2008).…”

“…However, the differential temporal regulation of eclosion (i.e. pupal-adult ecdysis) and emergence (''eclosion'' from the host puparium) in insects such as parasitic wasps, has been only addressed in Trichogramma (Reznik et al, 2008). In the present study we analyzed rhythms in activity, emergence, and eclosion in males of the parasitic wasp N. vitripennis, an organism previously used to study photoperiodism and which is now gaining much attention as an insect model system (Werren et al, 2010).…”

Cues for cavity nesters: investigating relevant zeitgebers for emerging leafcutting bees, Megachile rotundata

“…The distinction between emergence and eclosion is important because these events can be differentially regulated by environmental cues. For instance, eclosion in parasitic wasps, Trichogramma embrophagum, is not rhythmic, but their emergence from the host is regulated by a circadian rhythm (Reznik et al, 2008). We hypothesize that other Hymenoptera may behave similarly to T. embrophagum.…”

“…Solitary bees nest in light-restricted habitats, in below-or aboveground cavities, where thermoperiod may be an important cue because of the lack of light. One thing that differs between Hymenoptera and other insect taxa is that adult emergence often occurs several days after eclosion (Danforth, 1999;Kemp and Bosch, 2000;Yocum et al, 2015;Reznik et al, 2008;Bertossa et al, 2010). For example, adult bees shed their pupal cuticle (eclosion) and then remain in place for several days before exiting the brood cell (emergence).…”

Circadian Rhythms Differ between Sexes and Closely Related Species of Nasonia Wasps

“…Examples are locomotor activity [1], hatching [2], eclosion [3], emergence from host puparia [4], [5], and mating [6], [7]. Many of these circadian traits are expected to have an adaptive significance [8].…”