Diurnal rhythm of emergence from pupae in parasitic wasp<i>Trichogramma evanescens</i>Westw. (Insecta: Hymenoptera)

Abstract.A comparative study of the direct influence of single, non-repetitive changes of light and/or temperature on the daily pat tern of adult eclosion was conducted in laboratory conditions with the egg parasitoid, Trichogramma embryophagum (Hartig). In all experiments, the entire development occurred under the same regimen (12L : 12D, 20°C). However, just in the day when records of eclosion were made, the time of light-on was changed (from the total absence of a dark period to the 12-h-long scotophase). In addi tion, in different treatments of each experiment a thermophase (30°C during 2 or 4 hours) was applied in various positions relative to light-on. Results showed that light-on or a temperature step-up could induce eclosion in a certain percentage of individuals practi cally at any time of the 24-h-long cycle (masking effects). The fraction of adults emerging during 2 h after the beginning of the action of an exogenous factor depended not only on the preceding scotophase duration, but also on the stimulus itself (light, tempera ture or both). The temperature stimulus was found to modify the responsiveness to light considerably, depending on the order of application of the stimuli. The simultaneous action of light-on and a temperature step-up exerted a more considerable influence than could be expected based on their separate impacts. On the contrary, a high temperature pulse preceding the onset of the photophase inhibited the response of individuals to light-on, evidently acting by phase delay of a circadian rhythm of light responsiveness. These effects were more pronounced in the first half of the 12-h-long scotophase. The data suggest a complex interaction between the exogenous factors in their influence on the daily pattern of adult eclosion.

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

Reznik¹,

Войнович²,

Карпова³

2008

Eur. J. Entomol.

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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.

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Diurnal rhythm of emergence from pupae in parasitic waspTrichogramma evanescensWestw. (Insecta: Hymenoptera)

Cited by 3 publications

References 3 publications

The role of endogenous and exogenous factors in regulation of synchronous emergence of Trichogramma embryophagum Hartig and T. principium Sug. et Sor. (Hymenoptera, Trichogrammatidae)

The role of endogenous and exogenous factors in regulation of synchronous emergence of Trichogramma embryophagum Hartig and T. principium Sug. et Sor. (Hymenoptera, Trichogrammatidae)

Interaction of exogenous factors (light and temperature) in their influence on the daily pattern of adult eclosion in Trichogramma embryophagum (Hymenoptera: Trichogrammatidae)

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

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