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

Functional and numerical responses of Laricobius osakensis Montgomery and Shiyake and L. nigrinus Fender adults and larvae to its prey, Adelges tsugae Annand, were assessed in the laboratory. The functional response (ovisacs disturbed) of adult males, adult females and larvae of both species, was best described by a Type II functional response. The overall attack rates and handling times for L. osakensis males and females were similar. Attack rates for L. nigrinus males and females were similar and handling times differed significantly. Attack rates and handling times for females of both species did not differ significantly, but L. nigrinus males had both a greater attack rate and handling time than L. osakensis. When only considering A. tsugae adults killed, males of both species killed significantly more A. tsugae adults than females. Numerical response was measured as the number of eggs laid by the females. L. osakensis females showed a greater numerical response than L. nigrinus. Females laid eggs in several locations, L. osakensis preferred to lay the eggs under the adelgid while L. nigrinus preferred to lay the eggs in the wool. For the larvae, L. osakensis handling time was significantly less than L. nigrinus, while the attack rate was similar. The greater numerical response of L. osakensis combined with the greater functional response of L. osakensis larvae indicate this predator is potentially more effective in the control of A. tsugae populations.