PLANT-INSECT INTERACTIONS Relative Suitability of Virginia Pine and Loblolly Pine as Host Species for Dendroctonus frontalis (Coleoptera: Scolytidae)

Dendroctonus frontalis Zimmerman is a major disturbance agent in American pine forests, but attack preferences for various host species, and their relative suitability for reproduction, are poorly known. We studied patterns of beetle attack and reproduction during an infestation of stands containing Virginia pine and loblolly pine. Nearly all Virginia pine were attacked and killed, whereas a third of the loblolly pine escaped attack. Among attacked trees, the density of landings and attacks on Virginia pine was 56Ð106% higher than on loblolly pine at one site, whereas it was similar between species at another site. Paradoxically, D. frontalis preferred the host that was least suitable for reproduction: mean SE 0.89 0.33 versus 4.65 1.40 progeny/attack in Virginia pine versus loblolly pine. Poor reproduction in Virginia pine was attributable to increased adult mortality, decreased oviposition, and decreased larval survival. Phloem thickness and nitrogen content were similar between the two pine species. Loblolly pine was signiÞcantly more suitable for the growth of Ophiostoma minus, a fungal associate of D. frontalis. Resin ßow was lower in Virginia pine than in loblolly pine, although oleoresin chemistry may partly explain poor reproduction in Virginia pine. A simulation model predicted that beetle infestations will tend to collapse within stands dominated by Virginia pine, and that increasing availability of loblolly pinewill promote infestation growth. Because of beetle preferences, forests that contain evenmodest proportions of Virginia pine relative to loblolly pinemay be less likely to sustain beetle infestations.Management of species compositionmay provide a means for mitigating the undesirable impacts of this herbivore in pine forests.