In Japan, Pseudoscymnus tsugae Sasaji & McClure (Coleoptera: Coccinellidae) is a common and effective predator of Adelges tsugae Annand (Homoptera: Adelgidae), the hemlock woolly adelgid (HWA). Efforts since 1992 have focused on the development and use of P. tsugae as a means to lessen the destruction of HWA in the eastern United States.
P. tsugae is amenable to mass culturing and possesses other qualities that make it an excellent biological control candidate. P. tsugae produces three or more generations each year in the laboratory under controlled temperature conditions, it is adapted to a wide range of climate conditions, it strongly prefers to feed on adelgids, its life cycle is synchronized with that of HWA, and it has a high searching efficiency and dispersal ability.
Since 1995, 627,000 beetles have been released at 100 sites in 11 eastern states. P. tsugae has overwintered, established, reproduced, and spread at many of these release sites. At four sites in Connecticut and Virginia, a starting population of only 2,400 beetles reduced HWA densities on 40 monitored branches 43 to 87% in just five months.
Weather conditions from 1995 to 1999 hampered the biological control effort. A string of mild winters enhanced the survival and growth of HWA populations, and a severe drought in 1999 in the eastern United States, significantly reduced hemlock health. However, in the Northeast, a two-week period with sub-zero (F) temperatures in January, 2000 reduced adelgid populations by more than 90%, while P. tsugae survived this cold period. With greatly reduced adelgid numbers, hemlocks flourished during the cool, moist spring and summer of 2000 and abundant new growth was evident in spring 2001. Even though milder temperatures during winter 2000-2001 allowed 50 to 60% survival of HWA, pest densities have remained low in our release areas during 2001.
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA