Abstract
Seasonal adaptations of green lacewings (Neuroptera: Chrysopidae) and their role in the control of aphid populations are discussed. The chrysopids of temperate zones face seasonal changes and must escape cyclic adversity. One way is via the number of broods per year. Most green lacewings are facultatively multivoltine, with the succession of generations most often regulated by photomediated diapause. Others are univoltine and some extend their life-cycle to two years in cold or dry environments. Synchronization is an important feature of seasonality, often starting in spring. In univoltine species, it is sometimes the result of subtle mechanisms, such as double contradictory signals (short plus long day lengths) for reactivation in spring, or a multi-receptivity of the preimaginal instars to photoperiod throughout a year, combined with photo-controlled and synchronized egg laying in late summer. Only one North American species is known to enter a surnumerary food-mediated diapause in summer. Every postembryonic instar may undergo diapause depending on the species. The timing and impact of the spring resumption in aphid consumption depends on their overwintering strategy.As far is known, chrysopids are intolerant of freezing, but their supercooling points are low enough to enable them to endure hard frost. The numbers of overwintering specimens of green lacewings in the field depend on the structure of the assemblages in the previous growing season. Three examples are used to show that the overwintering populations are different in the different biotopes and dependent on the way the dominant species overwinter. Artificial chambers proposed for overwintering adults of common green lacewings afford them protection during diapause and enhance their predatory efficiency in spring.
Highlights
Organisms living at the higher latitudes are regularly confronted with seasonal changes in climate, which are more or less rigorously adverse and result in the evolution of strategies for escaping this cyclic adversity
Overwintering adults of the common green lacewings in North America survived well (97%) 31 weeks at 5°C when in a diapause-inducing photoperiod (Tauber et al, 1993). This is better than expected, based on their thermal thresholds of development, which are estimated to be 11–12 or 8–9°C in Chrysopa perla originating from western Europe (Canard & Principi, 1984) and Central Russia (Volkovich, 1998), respectively, and about 10°C in northeastern European strains of common green lacewings (Volkovich, 1998)
The time of resumption of predatory activity by green lacewings depends on their overwintering strategy, which determines their impact on aphid abundance (Fig. 1)
Summary
Organisms living at the higher latitudes are regularly confronted with seasonal changes in climate (cold/hot or dry/wet), which are more or less rigorously adverse and result in the evolution of strategies for escaping this cyclic adversity. Diapause and/or migration may offer ways of doing this. True migration (sensu Kennedy, 1975) may occur, but only, as far is known, in Chrysoperla carnea (Stephens, 1836), the so-called “common green lacewing”, which obligatorily flies down-wind on the first two nights after emergence, whatever the generation (Duelli, 2001)
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