Biological Control (Paperback)

Biological control, host resistance, and vegetative propagation were evaluated as strategies and tools for management of the exotic pest hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae) in the southeastern U.S. The suitability of the balsam woolly adelgid (BWA), Adelges piceae Ratzeburg, as an alternate rearing host for Sasajiscymnus tsugae was compared to the primary prey HWA in a series of laboratory-based paired-choice and no choice (single-prey) experiments that tested adult feeding, oviposition, and long-term survival and immature development of the predator. Results indicated that S. tsugae will feed equally on eggs of both prey, will accept both prey for oviposition, and that the predator's rate of immature development did not differ between the prey species, although fewer successfully completed egg to adult development on a diet of BWA compared to a diet of HWA. The long-term survival of predator adults was significantly influenced by both test prey type and the availability of a supplemental food source. The utility of confined releases for colonization of S. tsugae was evaluated in three field studies at forest and ornamental sites in western North Carolina. Predator reproduction, survival, and impact on HWA were investigated following the placement of fifteen adults (10 female:5 male) in mesh sleeves cages on adelgid infested hemlock branches for two or four weeks. In all three studies the predator reproduced inside sleeve cages and oviposition generally began within two or three weeks. Some adult predators were recovered during all three studies, indicating that S. tsugae can survive for up to one month inside mesh sleeve cages. Predator exclusion cages indicated significant local reductions in the density of adelgid ovisacs and aestivating nymphs, but these were not always correlated to the presence of the predator. Where S. tsugae was liberated from mesh sleeves two weeks after placement in the cages evidence of predator activity disappeared from the study sites within 4 months and establishment could not be documented during the study period. Differences in initial infestation rate and fecundity of HWA among three species of North American hemlock were evaluated in a climate-controlled greenhouse. Seedlings of adelgid-susceptible eastern, Tsuga canadensis (L.) Carriere, and Carolina, T. caroliniana Engelmann, hemlocks and putatively adelgid-resistant western hemlock (T. heterophylla Sargent) received either low inoculation (50 adeglid egg masses per seedling) or high inoculation (100 adelgid egg masses per seedling) treatments. Results showed very low and statistically similar rates of initial infestation on seedlings of Carolina and western hemlock and significantly higher rates on eastern hemlock seedlings. Adelgids that fed successfully on Carolina hemlock had significantly higher fecundity than those on either eastern or western hemlock, although this varied depending on inoculation treatment. The effects of auxin (NAA) concentration and cutting length on adventitious root formation in softwood stem cuttings from mature eastern and Carolina hemlocks were studied in a mist house. Overall rooting percentage (41%) and percent mortality (22%) were higher for eastern hemlock compared with Carolina hemlock (10% rooting and 13% mortality). Rooting percentage of each species responded differently to varying auxin concentrations (0, 1, 2, 4, 8 mM NAA), although the relationship between percent mortality and rooting was similar. Mortality among 6 cm stem cuttings was twice that observed for 3-cm cuttings of both species. However, 6 cm cuttings of eastern hemlock that did form adventitious...