The effect of twig diameter on emergence rates of the oak twig pruner (Coleoptera: Cerambycidae)

AbstractOak twig pruner (Anelaphus parallelus(Newman); Coleoptera: Cerambycidae) larvae develop inside twigs pruned from host plants. Reasons for this behaviour are unknown and differential emergence due to twig diameter has not been explored. Twigs pruned from walnuts (Juglans nigraLinnaeus; Juglandaceae) (n=179) and oaks (QuercusLinnaeus; Fagaceae) (n=84) were collected in Pennsylvania, United States of America in 2010; 118 pruned oak twigs were collected in New York State, United States of America in 2012. Twigs from 2012 were dissected to determine rates of emergence and larval mortality; both samples were examined for parasitoids. As the diameter of oak twigs (range of 3–16 mm) increased, larval mortality increased and adult emergence decreased. Date of collection did not influence twig diameter nor emergence rates. Three new parasitoids were associated with the oak twig pruner:AtanycolusFörster (Hymenoptera: Braconidae),Eubazus denticulatus(Martin) (Hymenoptera: Braconidae), and a potentially new genus of wasp (Hymenoptera: Braconidae, Hormiinae nearPambolusHaliday). Parasitism rates were an order of magnitude greater among twigs that contained more than one larva or pupa (23.1%;n=26) compared to those that contained only one (2.3%;n=341).