Biology and Host-Range Testing of Laricobius kangdingensis sp. n. (Coleoptera: Derodontidae), a Newly Discovered Predator of Hemlock Woolly Adelgid, Adelges tsugae Annand (Homoptera: Adelgidae)

by Gatton, Holly A.

The biology and host-specificity of Laricobius kangdingensis sp. n. (Coleoptera: Derodontidae), a new predator of hemlock woolly adelgid (HWA), Adelges tsugae Annand (Homoptera: Adelgidae) were investigated and compared with that of a related predator of HWA, L. nigrinus Fender. Adults became active in June 2003; the males emerged first and in greater numbers than the females. The sex ratio of female to male was 1: 1.1. Laricobius kangdingensis sp. n. has four larval instars. The total number of eggs laid between 7 July 2003 and 7 August 2004 was 1327. Mean lifetime fecundity per female was 196.4 ± 53.4 eggs and 97.9 eggs for the P1 (parental gen.) and F1 generations, respectively. In comparison, lifetime fecundity for F1 L. nigrinus was 100.8 ± 89.6 eggs.

Developmental rates were studied in fall 2003 and spring 2004. Combined with data gathered previously at 12 and 15ºC in early 2003, the 6, 9, and 18ºC data were used to determine lower temperature development thresholds for the egg (2.8ºC), larval (1.6ºC), and pre-pupal (5.8ºC) stages. The egg and larval thresholds are lower than those observed for L. nigrinus. Laricobius kangdingensis sp. n. individuals completed development only at 12 and 15ºC; however, these adults did not emerge from aestivation after pupation.

Laricobius kangdingensis sp. n. appears to be host-specific. In paired-choice feeding tests, adults consumed significantly more HWA than two other adelgid species [eastern spruce gall adelgid, Adelges abietis (L.), and pine bark adelgid, Pineus strobi (Hartig)], the pine needle scale, Chionaspis pinifoliae (Fitch), and the woolly alder aphid, Paraprociphilus tessellatus (Fitch). In paired-choice oviposition tests, females laid more eggs on HWA-infested eastern hemlock than on any other test prey. In no-choice host suitability experiments larvae fed on HWA; eastern spruce gall adelgid; the larch adelgid, A. laricis Vallot; the balsam woolly adelgid, A. piceae (Ratzeburg); pine bark adelgid; and pine needle scale, but not on woolly alder aphid or elongate hemlock scale, Fiorinia externa Ferris. Although no larvae completed development in any of the bioassays, 6 out of 15 larvae (40%) in the HWA treatment reached the pre-pupal stage. One larva out of 6 reached the pre-pupal stage on pine bark adelgid.