Why Do Populations of Southern Pine Beetles (Coleoptera: Scolytidae) Fluctuate?

Abstract

It is widely believed that population outbreaks of the southern pine beetle (Dendroctonus frontalts Zimm.) are caused by vagaries of climate, such as periods of severe drought. According to this view, D. frontalts population dynamics are dominated by densityindependent processes. We have statistically analyzed a So-yr record of D. frontalts activity in east Texas and have assessed the relative roles of density-independent and density-dependent factors in beetle population fluctuations. Regressionsof the rate of population change on three climatic variables were not significant. By contrast, both time-series and regression analyses provided strong and consistent evidence for delayed density regulation of D. frontalts populations. Thus, in contrast to previous analyses, we conclude that D. frontalts outbreaks are driven not by stochastic fluctuations of weather, but by some unknown population process acting in a delayed density-dependent manner. This result provides a starting point for a current study that will experimentally test various hypotheses concerning the role of natural enemies in D. frontalts cycles.

Dinâmica populacional da mariposa oriental em pomares de pessegueiro e ameixeira

“…Essas séries foram também analisadas com o software DCF para análise de correlação/autocorrelação, a fim de verificar a correspondência entre a ocorrência da praga e as flutuações de temperatura (Turchin et al, 1991).…”

“…As oscilações no número de indivíduos, amostrados em estudos de flutuação populacional, normalmente são atribuídas a fatores relativos ao clima, principalmente temperatura (Turchin et al, 1991;Logan & Allen, 1992;Berryman, 1996;Azerefgne et al, 2001). No entanto, diversos estudos de modelagem têm revelado a ocorrência de interações ecológicas, dinâmicas não lineares intrín-secas ou mesmo outros fatores não climáticos, regulando as oscilações de indivíduos (Turchin et al, 1991;Berryman, 1996;Grover et al, 2000;Rai & Schaffer, 2001).…”

“…No entanto, diversos estudos de modelagem têm revelado a ocorrência de interações ecológicas, dinâmicas não lineares intrín-secas ou mesmo outros fatores não climáticos, regulando as oscilações de indivíduos (Turchin et al, 1991;Berryman, 1996;Grover et al, 2000;Rai & Schaffer, 2001). Os surtos de ocorrência de Figura 6.…”

Complex emergence patterns in a bark beetle predator

“…In this scenario, each female produces both diapause and non-diapause offspring, with diapausers being favoured in more variable environments (Cohen, 1966;Ellner, 1985;Ellner, 1987;Hanski, 1988;Hopper, 1999). There is likely to be substantial variation of this type for T. dubius because the number of D. frontalis infestations (and hence prey availability) fluctuates greatly during the outbreak cycle (Turchin et& 1991). Alternatively, it may be that the pattern observed for T. dubius is a genetic polymorphism in which different genotypes either develop immediately or undergo diapause.…”

“…Tel: +1318 4737202;e-mail: jdreeve@attglobal.net U.S.A., and temperature-driven developmental models indicate that D. frontalis can complete about six generations per year (Ungerer et al 1999). Periodic outbreaks are a prominent feature of D. frontalis dynamics in the southern part of its range, with the number of infestations varying by three orders of magnitude between endemic and outbreak periods (Turchin et al 1991). A large community of natural enemies is associated with D. frontalis, arriving during mass attack or later on in brood development (Camors & Payne, 1973;Dixon & Payne, 1979b).…”