Species Assemblage Arriving at and Emerging from Trees Colonized by <I>Ips pini</I> in the Great Lakes Region: Partitioning by Time Since Colonization, Season, and Host Species

Abstract

The pine engraver, Ips pini (Say), colonizes jack, red, and white pines in the Great Lakes region. Males select suitable hosts, bore through the bark into phloem tissue, and emit aggregation pheromones. Pheromones attract conspecifics, which aid in overcoming tree defenses, and predators, which exploit these cues as kairomones. Sampling was conducted over 2 yr to characterize the assemblage of insects that arrive at and reproduce in trees colonized by I. pini, and how this assemblage is partitioned by host species, time after colonization, and seasonal phenology. Over 70 species from three orders were obtained. I. pini was most abundant, especially during late summer. The first natural enemy to arrive was Medetera bistriata Parent, which came simultaneously with I. pini. Other Diptera such as Lonchaea corticis Taylor and Zabrachia polita Coquillett were also abundant. Roptrocerus xylophagorum (Ratzeburg), a late instar parasitoid, arrived last. Its emergence most closely coincided with I. pini emergence, whereas the other species emerged substantially after I. pini. Host species did not affect total I. pini emergence but strongly affected natural enemies. Most R. xylophagorum and Monochamus spp. emerged from white pine, and most Z. polita emerged from red pine. I. pini had the highest ratio of emergence to arrival per log. Only the predator T. dubius and the parasitoid R. xylophagorum showed numerical responses to the number of emerging I. pini. Exclusion of insects during the first 2 wk of colonization decreased reproduction of I. pini and other wood borers in the spring, but not summer.