Temperature dependent development and survival of two sympatric species, Galerucella calmariensis and G. pusilla, on purple loosestrife

Abstract

Two sympatric Europeanbeetles, Galerucella calmariensis (L.)and G. pusilla (Duft.) (Coleoptera:Chrysomelidae), have been released in NorthAmerica for biological control of purpleloosestrife, Lythrum salicaria L.(Lythraceae). Because establishment isaffected by environmental conditions, studieswere conducted at temperatures ranging from12.5 to 30 °C to determine differencesin rate of development and survival between thetwo species. No egg hatch occurred at12.5 °C for both species. Eggdevelopment was faster for G.calmariensis than for G. pusilla attemperatures ≥ 15 °C. Theminimum threshold temperature for eggdevelopment was lower for G. calmariensisthan G. pusilla. At 12.5 °C, G. calmariensis larvae developed 1.6 daysfaster than G. pusilla, but at 15, 20,25, and 27.5 °C G. pusilla developed2.9, 1.2, 1.1, and 0.6 days faster,respectively, than G. calmariensis. Nodifferences in developmental rate of pupa andtotal development time from egg to adulteclosion were observed for the two species. However, survival of G. calmariensisgenerally was higher than that of G.pusilla at lower temperatures. No differencewas observed in the preoviposition periodbetween the two species except at27.5 °C. The preoviposition period forboth species at 12.5 and 15 °C exceeded50 days and was much higher than for20 °C and above. The long preovipositionperiod suggests that temperatures below15 °C induce reproductive diapause. At15 °C, G. pusilla females livedlonger and also had a longer oviposition periodthan G. calmariensis. However, fasteregg and larval development, and higher survivalat 12.5 °C may give G. calmariensisa competitive advantage over G. pusillain cooler climates.