Catching the right flight: Cues eliciting attachment and detachment behaviors by mites phoretic on the pine engraver, Ips pini (Say)

Our surveys have recorded over 20 species of phoretic mites associated with pine engravers, Ips pini, in Wisconsin. Mites feed and develop on various resources present within the degrading pine phloem made available by these tree-killing beetles. As the phloem resource degrades further, some mites shift from reproductive to phoretic behavior and utilize emerging brood adult bark beetles for transport to a new resource. Timing can be important, because pine engravers utilize a tree for a single generation lasting less than two months, while mite food sources as well as other beetle species capable of phoresy inhabit the phloem for longer periods. While aspects of the transport process are well understood for some mites, the cues used to trigger attachment and detachment remain largely unexplored for most species. We conducted a series of manipulative laboratory bioassays to assess chemical and mechanical cues eliciting attachment and detachment behaviors by the three most prominent phoretic mites of pine engravers in Wisconsin, Dendrolaelaps quadrisetus, Iponemus confuses, and Histiogaster arborsignis.  We selected these species because they utilize different feeding substrates (nematode feeder, generalist scavenger/fungal feeder, predator on beetle eggs and larvae, respectively), experience varying durations of time during which the killed-tree habitat provides suitable resources, and show differing degrees of association with I. pini.  Results suggest that host plant terpenes and beetle death may elicit detachment behavior. Compounds associated with sclerotization of adult beetles may provide important cues for attachment.