Feeding, Survival, and Fecundity of Adult Emerald Ash Borer (Coleoptera: Buprestidae) on Foliage of Two Novel Hosts and Implications for Host Range Expansion.

Insect herbivores are more likely to successfully use a novel host if the plant is closely related to the ancestral host and the insect is polyphagous. Emerald ash borer (EAB), Agrilus planipennis (Fairmaire) (Coleoptera: Buprestidae), is a specialist wood borer of ash (Fraxinus spp., Lamiales: Oleaceae) trees and one of the most destructive forest pests in North American forests. Recent studies have found that larvae can develop in stems of two ash relatives; white fringetree (Chionanthus virginicus (L.) [Laminales: Oleaceae]) and cultivated olive (Olea europaea (L.) [Laminales: Oleaceae]). For EAB adults, the ability to consume, successfully mate, and lay viable eggs on foliage of these hosts is unknown. Thus, we conducted two no-choice assays with adult EAB on foliage of white fringetree and olive paired with positive controls of susceptible ash. Larval performance was also examined in a reciprocal study with cut stems of white fringetree and green ash (Fraxinus pennsylvanica Marshall) to determine whether adult diet impacted the success of progeny. Longevity, consumption rates, and fecundity of adults were similar on white fringetree and ash foliage. In contrast, adults consuming olive died quickly, consumed more over time, and females laid far fewer eggs compared to those on ash. Adult diet did not impact larval success, but larvae in white fringetree stems grew slower. These results indicate that white fringetree is a suitable host for EAB to complete its lifecycle, although larvae perform more poorly on this host than in susceptible ash species. In contrast, the more distantly related olive appears to be a poor host for adult EAB, although some viable eggs were produced by females.

Differences in Early Season Emergence and Reproductive Activity Between Spathius agrili (Hymenoptera: Braconidae) and Spathius galinae, Larval Parasitoids of the Invasive Emerald Ash Borer (Coleoptera: Buprestidae).

Both Spathius agrili Yang and Spathius galinae Belokobylskij and Strazanac are host-specific parasitic wasps introduced for biological control of emerald ash borer in North America. Spathius agrili is native to northeastern China and S. galinae comes from a more northern, colder climate in the Russian Far East. Their origin may lead to differing abilities to adapt to climate and their host in North America. We conducted both field and laboratory experiments to determine the timing of early season emergence and synchronization of each parasitoid species to their host in the United States, and if manipulating prerelease conditions could affect emergence time. A cold acclimatization treatment prior to parasitoid emergence was assessed and compared with untreated control group reared with standard rearing protocols. Stands of naturally emerald ash borer-infested ash were sampled at two locations in Virginia throughout the experiment to determine when the parasitoid-susceptible life stage (third to fourth instar) occurred. Untreated S. galinae emerged approximately 2 wk earlier than any other cohort, whereas cold acclimatized S. galinae emerged later than any other cohort. Emergence time of S. agrili was unaffected by cold acclimatization. Cold acclimatization treatment did not affect the parasitism rate of either species, nor did it have multigenerational effects. Emergence time of the subsequent generation of S. agrili was delayed by cold acclimatization treatment, whereas S. galinae experienced no multigenerational effects. At Virginia field sites, susceptible EAB larvae were present during the emergence time of all four groups of parasitoids. Untreated S. galinae had the least overlap with any susceptible EAB larvae.