Life history and overwintering tactics of Velia caprai tam. (Hemiptera: Veliidae) in Southern Ireland
Title:
Life history and overwintering tactics of Velia caprai tam. (Hemiptera: Veliidae) in Southern Ireland
Author:
Murray, A. M. Giller, P. S.
Appeared in:
Aquatic insects
Paging:
Volume 13 (1991) nr. 4 pages 229-243
Year:
1991
Contents:
Velia caprai Tamanini (Hemiptera: Veliidae) is predominantly a stream dweller, and has been considered univoltine in the British Isles, with adults overwintering in a reproductively immature state. This study reveals a far more complex life-cycle. Dissections of females captured between October 1986 and March 1987 revealed that while 17% of individuals had deposits of adipose tissue and showed no reproductive development (diapause individuals), the majority of females examined (83%) revealed mature ovaries. This presence of a non-diapause overwintering subpopulation of reproductively mature females has not been previously recorded for this species. The absence of adipose tissue in these latter females, plus the presence of obviously full guts in 24% of cases—indicating very recent feeding—supports this non-diapause overwintering. Sampling also revealed that fifth instar larvae overwintered and these comprised 2.3% of all individuals (excluding first instar larvae) captured between November 1986 and March 1987. Three different overwintering tactics were therefore identified with early spring populations therefore consisting of mature egg-bearing females, immature females and some fifth instar larvae. Information from less complete data of spring 1986 confirmed that the variation in the overwintering status of females in 1987 was not a once-off response to unusual climatic conditions. This distinct within-population temporal variability in the attainment of reproductive maturity by the females of Velia caprai extended the reproductive season of the species, and may help buffer populations from being overly affected by adverse weather conditions during the late autumn and early spring months. First instar larvae were encountered in the field by mid-March—two months earlier than previous records. New-generation adults were subsequently captured in mid-June, and there is indirect evidence to suggest a partial second generation may sometimes occur under suitable circumstances. Growth experiments over a range of temperatures indicated faster development at the higher temperatures, although a reduced survival rate at temperatures above 20°C was noted.
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