Functional and numerical response of Laricobius spp. predators (Coleoptera: Derodontidae) on hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae)

Laboratory studies were carried out to determine the functional and numerical responses of the adults and larvae of Laricobius osakensis Montgomery and Shiyake and Laricobius nigrinus Fender to different densities of its prey, Adelges tsugae Annand. Males, females and larvae of both species showed a type II functional response. Overall attack rates and handling times for L. osakensis males and females were comparable. For L. nigrinus males and females, attack rates were similar but handling times differed significantly. Females of both species had the same attack rates and handling times, but L. nigrinus males showed a higher attack rate and longer handling time than L. osakensis males. Males killed significantly more A. tsugae adults than did females for both species, but there were no significant differences between species. The number of eggs laid by the predators (numerical response) as a function of A. tsugae density (d) was modeled by the equations: n(e) = 2.6691 ln(d) + 3.4135 and n(e) = 2.3863 ln(d) - 0.5356 for L. osakensis and L. nigrinus, respectively. L. osakensis laid significantly more eggs than L. nigrinus for all prey densities. While L. osakensis preferred to lay the eggs under the A. tsugae adults, most L. nigrinus eggs were in the wool. Attack rates were similar, but L. osakensis larvae handling time was significantly less than that of L. nigrinus larvae. The higher numerical response, combined with the higher functional response of L. osakensis larvae indicates that this species can potentially be more effective than L. nigrinus. (C) 2012 Elsevier Inc. All rights reserved.