Field-cage evaluation of the survival, feeding and reproduction of Laricobius osakensis (Coleoptera: Derodontidae), a predator of Adelges tsugae (Hemiptera: Adelgidae).
The hemlock woolly adelgid, Adelges tsugae Annand, is a serious, non-native pest of hemlock in eastern North America. Laricobius osakensis Montgomery and Shiyake was identified as a key predator in Japan, where A. tsugae is native. Performance of adult and immature stages of L. osakensis was evaluated in sleeve cages on adelgid infested Tsuga canadensis (L.) Carrière in plant hardiness zones 5b and 6b in the mountains of southwestern Virginia, USA. Adults fed on the adelgid and laid eggs during all biweekly sample periods from December 2010 to May 2011, including winter when the temperature averaged below 0°C. In cages with one adult pair (one male and one female), predation of A. tsugae/predator was 0.3-0.9/day during December and January, increased to 2.5/day in February, and then declined to 0.15/day in early May. The oviposition rate lagged the changes in feeding by 2-4 weeks, increasing from 0.02 eggs/day, from December to mid-January, to a peak of 1.5 eggs/day in early April, then declining to 0.4 eggs/day in late April. Mortality was 20% in cages left undisturbed for two months during the winter; even though temperatures were as low as -18°C (cages examined biweekly had higher mortality, likely due to disturbance). In cages left undisturbed for two months during winter or early spring, 34 and 37 progeny were recovered, respectively. During each bimonthly period, a pair of adults and their progeny consumed 2.5 and 2.4 adult adelgids or ovisacs per day, respectively. Twenty-eight days after eggs were placed in the cages (on 11 March or 27 April 2012), 48% and 95% of the recovered larvae had reached maturity and each larva had destroyed 43 and 39 ovisacs, respectively. This research indicates that L. osakensis may have the potential to be an effective biological control agent of A. tsugae in most of the area where it is a pest in the eastern US.