Temperature-dependent development in Chrysomela vigintipunctata (Coleoptera: Chrysomelidae), a stenothermal early-season breeder

Chrysomela vigintipunctata (Scopoli) is a univoltine leaf beetle commonly encountered on willows across the Palearctic forest zone. The preimaginal development in this species takes place during a short time period, from May to June, because larvae are unable to consume mature leaves of the host plant. Therefore, the diet quality imposes a time constraint, and it was expected that the temperature dependence of development in C. vigintipunctata should be adaptively adjusted to the shortness and cool conditions of the favorable season. It was experimentally determined that this leaf beetle was stenothermal at the larval stage, required 275.5 degree-days above the threshold of 9.0 °C for total development from oviposition to adult emergence, and attained greater body mass at lower temperatures. However, in all of these aspects, the thermal ecology of C. vigintipunctata was similar to that of two related multivoltine species, C. populi and C. scripta. The interspecific similarity of thermal reaction norms for development rate and body size suggests that these reaction norms in C. vigintipunctata were unlikely to have been shaped by selection favoring faster development or growth early in the season. The results are discussed in terms of the “ecological fitting” concept, which states that a species may be successful in exploiting novel environments while retaining ecophysiological traits evolved elsewhere.