Technique for Rearing Mite-Free Southern Pine Beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), Adults1

Abstract

Southern pine beetles can be reared free of phoretic mites from naturally infested bark if the bark is removed from the tree and air dried. Bark removal does not reduce the number of beetles that emerge. On the average fewer than 1 % of the beetles emerging from removed bark carried one or fewer mites, and 85% of the beetles emerging from attacked bark carried one or more mites. Seven species of mites were found on beetles emerging from attached bark. About 15 species of mites are commonly transported by the southern pine beetle (SPB), Dendroctonus .fron- talis Zimmermann 1868 (Moser and Roton 197 1, Kinn 19761, with the proportion of phoretized flying adults conservatively estimated at 40% (Moser 1976). The trophic habits of these phoretic mites range from predaceous, mycophagous, nematophagous, or sapro- phagous to various combinations of feeding preferences. Some are detrimental to the SPB, others are neutral or beneficial (Kinn 1967, 1980, Moser, 1975, Wilson 1980). Many numerous and complex relationships exist among these mites and the SPB; hence mites should be excluded from studies to determine the capacity of SPB to attack trees and produce broods in the absence of selected as- sociates. At present there are no efficient methods for obtaining large numbers of SPB free of phoretic mites. Mechan- ically removing mites invariably injures the beetles be- cause the elytra have to be lifted. Rearing beetle adults from eggs on artificial media is tedious and time con- suming; very few adults are produced (Bridges 1979). Kinn (1979) first documented that desiccation of the phloem killed some mite species. Subsequent studies by the authors showed that desiccation might severely re- duce or eliminate all mite populations, resulting in vir- tually no phoretic mites on emerging beetles. In this study we decided to see whether mite-free populations of SPB could be reared from desiccated host material. Materials and Methods Four loblolly pines (Pinus tneda L.) infested with SPB were cut during February, May, August, and De- cember 1980. The trees were from a natural stand about 35 years old in Catahoula Ranger District of the Kis- atchie National Forest. Trees were felled when the SPB broods were pupae in the outer bark. Pupae do not carry phoretic mites (Roton 1978). Samples were taken from the bole area where the pupal stage was most concentrated and where compe- tition from other bark beetle species was least. Typi-