What causes outbreaks of the gypsy moth in North America?

Abstract

The gypsy moth has been present in North America for more than 100 years, and in many of the areas where it has become established outbreaks occur with varying degrees of periodicity. There also exists extensive spatial synchrony in the onset of outbreaks over large geographic regions. Density-dependent mortality clearly limits high-density populations, but there is little evidence for strong regulation of low-density populations. Predation by small mammals appears to be the major source of mortality affecting low-density populations, but because these are generalist predators and gypsy moths are a less preferred food item, mammals do not appear to regulate populations in a density-dependent fashion. Instead, predation levels appear to be primarily determined by small mammal abundance, which is in turn closely linked to the production of acorns that are a major source of food for overwintering predator populations. Mast production by host oak trees is typically variable among years, but considerable spatial synchrony in masting exists over large geographic areas. Thus, it appears that the temporal and spatial patterns of mast production may be responsible for the episodic and spatially synchronous behavior of gypsy moth outbreaks in North America. This multitrophic relationship among mast, predators, and gypsy moths represents a very different explanation of forest insect outbreak dynamics than the more widely applied theories based upon predator-prey cycles or feedbacks with host foliage quality.

Prey choice, provisioning behaviour, and effects of early nutrition on nestling phenotype of titmice

“…Hairy caterpillars do not occur commonly in the great tit diet, although some species are able to cyclically reach outbreak numbers (e.g., Liebhold et al, 2000). For instance, Pimentel and Nilsson (2007; reported that Portuguese great tits exploited nests containing larvae of T. pityocampa (Notodontidae) during the winter period when there were no other caterpillar species available.…”

Comparative population genetic study of two oligophagous insects associated with the same hosts

“…In this context, natural selection has probably favoured females with bigger egg masses rather than high dispersal abilities. It is noticeable that some other forest lepidopteran defoliators such as the European gypsy moth Lymantria dispar (L.) and the winter moth Operophtera brumata (L.) exhibit similar patterns of low female dispersal combined with large egg masses (Van Dongen et al, 1996;Liebhold et al, 2000). Likewise, the gregarious sawflies Diprion pini L. and Neodiprion sertifer (Geoffroy) probably evolved under comparable ecological constraints and could be expected to exhibit the same patterns of population differentiation owing to a reduced mobility associated with a higher reproductive allocation (Codella and Raffa, 1993;Herz and Heitland, 2002).…”

Foraging ecology of black bears in urban environments: guidance for human‐bear conflict mitigation

“…During hyperphagia, masting plant species that produce acorns, nuts, and berries provide bears with high caloric energy that is critical for survival and reproduction (Rogers et al 1976, Inman and Pelton 2002, McDonald and Fuller 2005, Mosnier et al 2008. But mast crops can fail due to unfavorable weather conditions, e.g., late-spring freezes and droughts (Sharp andSprague 1967, Neilson andWullstein 1980), or disease outbreaks (Liebhold et al 2000), resulting in bears seeking alternative food sources (Baruch-Mordo et al 2014). Use of anthropogenic food resources can lead to behavioral adaptations and changes to bear ecology Berger 2003a, Baruch-Mordo et al 2014) and result in increased human-bear conflict (Oka et al 2004, Baruch-Mordo et al 2008.…”