Current Status and Critical Research Needs in Scolytid Genetics1

During the past two decades, our knowledge of bark beetle behavior and ecology has greatly expanded. In particular, stud­ ies of pheromone communication, host plant relations, and population dynamics have increased our basic knowledge of bark beetle biology, improved our ability to manage pest spe­ cies, and provided strong models for research on other insect groups. However, bark beetles remain our most damaging forest pests nationwide. In addition, the various components of scolytid biology are usually studied in isolation, and some key gaps in our knowledge preclude effective synthesis. In my opinion, a major reason for these difficulties is that insufficient attention has been given to bark beetle genetics. Increased knowledge in this area could serve as a powerful unifying theme among the various subdisciplines, and improve our man­ agement capabilities. The lack of attention to scolytid genetics is well evidenced by the major books and review articles on this family. Most texts and chapters make no, or relatively brief, mention of genetics or the role genetics could play in population behavior. Some areas of scolytid genetics have received well-focused attention, in particular isozyme variation within and between species (Langor and Spence 1991, Stock and Guenther 1979, Stock and others 1984). These studies established polymor­ phism, heterozygosity, and population structuring across geo­ graphic regions and sometimes host species. Some basic work has been done on cytology (e.g., Lanier 1981), before the development of modern methods. However, a number of criti­ cal areas, ranging from the molecular to population levels, remain unexplored. A number of new tools are now available for studying insect genetics. However, I feel the most critical need is to generate testable hypotheses regarding how heritable aspects of scolytid biology relate to their behavior and population dynam­ ics. Milton and Schneider (1987) summarized two basic ap­ proaches to the role of genetics in insect outbreaks: (1) start with a heritable marker, and conduct a broad search for correla­ tions between gene frequencies and population fluctuation, and (2) identify life history traits whose variation would greatly influence population behavior, and determine heritable varia­ tion. Both approaches are valid, and both must be pursued to make relevant gains. As a population ecologist, I will approach the issue from the latter perspective. Hopefully, this perspec­ tive will complement equivalent suggestions arising from the marker-up, and more molecular approaches. From an ecologi­ cal/population management view, I think that three critical genetic issues must be addressed.