Rearing of two predators, <i>Thanasimus dubius</i> and <i>Temnochila virescens</i>, for the biological control of <i>Ips grandicollis</i> in Australia

Abstract

Abstract Rearing methods for two coleopterous predators, Thanasimus dubius and Temnochila virescens , imported into Australia for the biological control of Ips grandicollis , were developed. Bionomic data obtained from laboratory rearings between 1982–1987 showed that T. dubius eggs took about 7 days to hatch and that duration of the larval stage was about 42 days. Observations showed that T. dubius had a prolonged prepupal stage (x̄ = 56.4 days, range 14–274 days), which was probably non‐diapausal in nature. Mean adult longevity was 50 days (range 1–358 days). Temnochila virescens eggs took almost 9 days to hatch, and a lengthy larval stage (x̄ = 155.4 days, range 73–333 days) was observed. Mean duration of the pupal stage was 14 days (range 7–28 days). A long preoviposition period (x̄ = 141 days, range 47–206 days) was observed, and adults were very long‐lived (x̄ = 232.7 days, range 14–667 days). Capacity for increase (r c ) calculated from rearing data suggested that numbers of T. dubius could be increased faster than T. virescens. Mortality between 1982–1987 averaged about 70% for both species. However, mortality of T. dubius in 1987 increased significantly, suggesting that inbreeding or other methodological factors could be responsible. A mass‐rearing method using Ips ‐infested pine billets was developed as a cheaper alternative to laboratory rearing, and was shown to be effective in producing large numbers of insects for release.