Eur. J. Entomol. 105 (1): 81-85, 2008 | DOI: 10.14411/eje.2008.011

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

Sergey Ya. REZNIK, Natalia D. VOINOVICH, Nina P. VAGHINA, Svetlana G. KARPOVA
Zoological Institute, Russian Academy of Sciences, 199034 St. Petersburg, Russia; e-mail: reznik@MD12306.spb.edu

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, 20C). 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.

Keywords: Parasitoids, Hymenoptera, Trichogramma, circadian rhythms, photoperiod, pupal-adult ecdysis, adult emergence

Received: June 26, 2007; Accepted: July 16, 2007; Published: February 15, 2008

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