Pre-release Evaluation of Laricobius osakensis Montgomery and Shiyake (Coleoptera: Derodontidae), a Potential Biological Control Agent for the Hemlock Woolly Adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), in the Eastern United States

Hemlock woolly adelgid, Adelges tsugae Annand, is an invasive pest threatening eastern (Tsuga canadensis (L.) Carrière) and Carolina hemlock (T. caroliniana Englem.) forests in the eastern US. A new predator, Laricobius osakensis Montgomery and Shiyake, has been found in association with A. tsugae in Japan. Laricobius osakensis was evaluated in a series of pre-release studies to assess its potential as a biological control agent for A. tsugae. Host-range studies indicated that L. osakensis is a specific predator that feeds predominantly and reproduces only on A. tsugae. The functional response "prey consumption changes in response to changes in prey density" was similar for both L. osakensis and Laricobius nigrinus Fender adults. However, L. osakensis had a higher numerical response"changes in oviposition in response to changes in prey density"than L. nigrinus. Laricobius osakensis larvae had a higher functional response than L. nigrinus larvae. Laricobius osakensis' higher numerical and functional response indicates that this species can potentially be more effective than L. nigrinus. In the evaluation of L. osakensis in sleeve cages in the field from December to April high rates of adult survival, feeding, and reproduction were found. A pair of predators in a cage killed on average five adelgids/day. Peak oviposition occurred in March and April. Larvae from eggs placed in the cages reached maturity in 28-50 days, depending on the season, and only 6.7 % died before reaching maturity. Laricobius osakensis was able to survive, feed, develop, and reproduce in USDA cold-hardiness zones 5b and 6a of southwest Virginia. Behavior of L. osakensis and L. nigrinus was qualitatively similar but varied quantitatively. Laricobius osakensis was more active and had a lower association with T. canadensis. Interactions between species were minimal and not detrimental to either. Intrasexual copulation attempts were observed between males and to a lesser extent between females; however, intrasexual interactions were less frequent than intersexual interactions between the two species. Otherwise activity, including oviposition, was not altered by the presence of the other species. These studies indicate that L. osakensis has the potential to be a valuable addition to the natural enemies complex against A. tsugae.