Abstract
Only in the southern part of the Iberian Peninsula the large white butterfly Pieris brassicae was recorded to pass the summer in pupal aestivation, induced by long-day photoperiods. It is not clear why this photoperiodic response is regionally restricted. We investigated whether the change of life history in P. brassicae may affect the infestation by parasites. This was done by testing the coincidence of photoperiodic responses in both the host P. brassicae and in its main parasitoid Cotesia glomerata. While the response under short-day conditions was very similar in both species, no summer dormancy of any type was found in the parasitoid at photophases >= 15h and temperatures of 15°-25°C in contrast to 100% aestivation in the host. We suggest that aestivation is a response which allows the host to desynchronise its life cycle from that of its parasitoid. This is effective because parasitoid wasps cannot pass the temporary absence of suitable host stages by a similar developmental rest. C. glomerata is then forced to switch to less adequate host species which diminishes its reproductive success.
Highlights
The photoperiodic response of the large white butterfly, P. brassicae L., has been known as a typical long-day type (Beck, 1980), i.e. long photophases induce a non diapause response (Danilevskij, 1965; Spieth, 1985)
In this paper we investigate whether parasitism may effect the evolution of aestivation
To show whether a summer diapause could be induced in C. glomerata, parasitised larvae of P. brassicae were reared at 15°C and photophases between 10 h and 16 h
Summary
The photoperiodic response of the large white butterfly, P. brassicae L., has been known as a typical long-day type (Beck, 1980), i.e. long photophases induce a non diapause response (Danilevskij, 1965; Spieth, 1985). A locally restricted population has been found in southern Spain which surprisingly exhibits another response type showing a dormancy under long photo phases as well (Held & Spieth, 1999). This short-day/long-day response type (Beck, 1980) undergoes two developmental rests, a winter dormancy (= hiberna tion diapause) and a summer dormancy (= aestivation dia pause). There must be a strong selective pres sure on the conservation of this behaviour (Held & Spieth, 1999) because all individuals from the tested Ibe rian populations endure the summer months in a stage of aestivation
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