Abstract
Insects experience important selection pressures from their parasitoids, which affect both their population dynamics and their evolutionary responses. The interaction between the egg parasitoid Oomyzus galerucivorus Graham (Hymenoptera: Eulophidae) and its chrysomelid host Galeruca tanaceti L. (Coleoptera: Galerucinae) was investigated with the particular aim deter- mining whether the chrysomelid host can escape its parasitoid by ovipositing late in the year as early as September. Although the leaf beetle and its parasitoid emerge in April, G. tanaceti starts to oviposit after spending the summer in reproductive diapause. The objective was to determine, whether the small parasitic wasp can parasitise its host's eggs even at the end of its host's reproductive season in December, when temperatures are low. Beetle oviposition, parasitism rates and temperatures were measured on three com- parable mesoxerophytic grassland sites over the coarse of a season. Beetle oviposition, but not parasitism, was significantly posi- tively dependent on temperature. Rate of oviposition decreased over the oviposition period with decrease in temperature. In contrast, after a lag phase of 1-2 weeks at the beginning of the oviposition period in September beetle egg clutches were parasitised at a con- stant rate until the end of the season in December. Host eggs were parasitised even at mean daily temperatures of 0-6°C. Thus the tansy leaf beetle does not escape from egg parasitism by ovipositing late in the season in central Germany.
Highlights
Parasitoid-host interactions are characterised by the hosts’ attempts to escape parasitism and the parasitoids’ efforts to follow their hosts (e.g., Price et al, 1980)
The interaction between the egg parasitoid Oomyzus galerucivorus Graham (Hymenoptera: Eulophidae) and its chrysomelid host Galeruca tanaceti L. (Coleoptera: Galerucinae) was investigated with the particular aim determining whether the chrysomelid host can escape its parasitoid by ovipositing late in the year as early as September
When the oviposition activity stopped in the middle of December, 1017 egg clutches had been located at Schafhof, 362 at Prappach, and 475 at Rauchberg, respectively
Summary
Parasitoid-host interactions are characterised by the hosts’ attempts to escape parasitism and the parasitoids’ efforts to follow their hosts (e.g., Price et al, 1980). Might gain enemy free space by changing their temporal activity patterns (Price et al, 1980; Jeffreys & Lawton, 1984; Berdegue et al, 1996), e.g. when they are active under environmental conditions that affect the parasitoids more negatively than themselves. Due to their small size and associated thermoregulatory constraints (Willmer, 1985) egg parasitoids might be more strongly physiologically restricted and experience a higher mortality or might be less active in unfavourable environmental conditions (e.g., at high or low temperatures and in drought conditions) than their much larger hosts. There are only a few studies on the phenology of host-parasitoid interactions and even fewer consider the effect of temperature or evaluate the existence of enemy free space in time for the host (Clancy & Price, 1987; Strohm et al, 2001)
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