Comparison of reproductive capacity among univoltine, semivoltine, and re-emerged parent spruce beetles (Coleoptera: Scolytidae)

Abstract

Abstract New spruce beetle, Dendroctonus rufipennis (Kirby), adults of univoltine and semivoltine life cycles, as well as re-emerged parent beetles, were laboratory-tested for differences in reproductive capacity and brood characteristics. Parameters measured from the three groups include dry weight, lipid content, and egg production. Brood characteristics measured include egg length, development rates, and survival densities. Although there were some differences in dry weight and lipid content, females from the univoltine, semivoltine, and re-emerged parent groups did not greatly differ in egg production. Egg length was slightly smaller for eggs from univoltine parents, but other measured brood characteristics did not differ among the three parent groups, including the density of the surviving brood. In a field study, re-emerged parent beetles were determined to be flight capable. These findings imply that populations with univoltine broods will have higher growth rates than semivoltine populations. Consequently, the presence of univoltine broods, which is weather dependent, increases the risk of a beetle outbreak or can accelerate the rate of spruce mortality in an established outbreak. These results also indicate that re-emerged parent beetles can contribute substantially to brood production. Suppression strategies can be more effective if managers consider the ecological consequences of brood production from the three parent groups.