EVALUATION OF THE RE-EMERGENCE PROCESS OF PARENT ADULT DENDROCTONUS FRONTALIS (COLEOPTERA: SCOLYTIDAE)

Abstract

AbstractThe process of re-emergence of Dendroctonus frontalis parent adults was investigated using emergence traps placed systematically along the bole of infested loblolly pine, Pinus taeda. Daily collections of the traps showed the re-emergence pattern by height through time. Re-emergence/100 cm2 (Y) was described as a function of time (X) by the model Y = C(18X)B−1 exp (−A(18X)B) + ɛε for intervals along the infested bole. Peak re-emergence occurred shortly after peak attack density and continued 16–20 days. Highest re-emergence density occurred at the midportion of the infested bole and tapered to the ends. The same model was used to describe re-emergence as an average process for the entire tree. For convenience in evaluating expected re-emergence totals over a time span, the cumulative form of the model was fit to the data. The proportion of re-emergence was studied using bark samples taken at the beginning and end of the process and was found to be 97% of the attacking adult population. An empirical distribution function was developed and the probability of re-emergence described using the function Y = ABCXB−1 exp (−AXB) + ɛε, where Y = the probability of re-emergence at a time X in days given that a beetle was present on day 1 of the process. The cumulative form of this model was also provided.Using laboratory bioassays parent adults were tested and found to respond to the attractant mixture of frontalin, trans-verbenol, and loblolly pine turpentine.Re-emergence may play several functions in the population dynamics of D. frontalis: conditioning host trees through mass colonization; establishing brood populations through multiple re-emergence, thereby efficiently allocating egg populations; identifying new hosts and aggregating populations through pheromone production; and maintenance of continuity in pheromone production at the active portion of the infestation, thereby identifying the location of trees under colonization. The prolonged re-emergence period was suggested to be of survival value to the insect in that local short term disasters would affect only a small proportion of the re-emerging population. The number of re-emergences and proportions of re-emergence were suggested to be related to oviposition per parent adult and hence attack density.