Population fluctuations of the western tent caterpillar in southwestern British Columbia

Abstract

Cyclic populations of western tent caterpillars fluctuate with a periodicity of 6-11 years in southwestern British Columbia, Canada. Typically, larval survival is high in early stages of the population increase, begins to decline midway through the increase phase, and is low through several generations of the population decline. Fecundity is generally high in increasing and in peak populations but is also reduced during the population decline. Poor survival and low fecundity for several generations cause the lag in recovery of populations that is necessary for cyclic dynamics. The dynamics of tent caterpillar populations vary among sites, which suggests a metapopulation structure; island populations in the rainshadow of Vancouver Island have more consistent cyclic dynamics than mainland populations in British Columbia. Sudden outbreaks of populations that last a single year suggest that dispersal from source to sink populations may occur late in the phase of population increase. Wellington earlier discussed qualitative variation among tent caterpillar individuals as an aspect of population fluctuations. The variation in caterpillar activity he observed was largely statistically nonsignificant. Recent observations show that the frequency of elongate tents as described by Wellington to characterize active caterpillars varies among populations but does not change in a consistent pattern with population density. The level of infection from nucleopolyhedrovirus (NPV) was high in some populations at peak density but was not associated with all population declines. Sublethal infection can reduce the fecundity of surviving moths, and there is a weak association between viral infection and egg mass size in field populations. The impact of weather in synchronizing or desynchronizing populations is a factor to be investigated further.

Biological activity and identification of nucleopolyhedroviruses isolated from Mythimna separata and Spodoptera litura in Japan

“…Therefore, it is likely that SpltNPV S infects very few species, and this property can be ecologically beneficial for pest control. However, we cannot exclude the possibility of pernicious or sublethal infection, which can have an important impact on host-pathogen dynamics (Myers and Kukan 1995;Myers 2000).…”

The effect of food limitation on immunity factors and disease resistance in the western tent caterpillar

“…An important characteristic of declining tent caterpillar populations is a reduction in the sizes of egg masses (Myers 2000;Cory and Myers 2009). The experimental reduction of food availability in our experiment caused the egg masses of food-restricted parents to be smaller than those of fully-fed parents, even though they received full-food in the 5th instar.…”

“…A good example of population cycles are those of western tent caterpillars, Malacosoma californicum pluviale, in the PaciWc Northwest of North America where, since 1936, outbreaks have been recorded to occur every 6-11 years (Myers 2000;Cory and Myers 2009). As with several other members of the families Lymantriidae and Lasiocampidae that demonstrate population cycles (review in Cory and Myers 2003), epizootics of nucleopolyhedrovirus (NPV) are associated with population declines of western tent caterpillars.…”

Dendrochronological reconstruction of forest tent caterpillar outbreaks in time and space, western Manitoba, Canada

“…Trees in the PTR-PBA site type may have been especially susceptible to moisture stress, as jack pine generally grows on dry sites throughout its range and is known to grow on rock outcrops in the boreal forest (Sims et al 1990). Although it has been difficult to directly link environmental factors to the cyclic patterns of insect outbreaks (Myers 2000), several factors may affect the relationship between defoliating insects and their hosts causing increased weakening of the hosts (Mattson and Haack 1987). This additional weakening may lead to increased fungal and microbial infection in the affected trees (Mattson and Haack 1987;Sutton and Tardif 2005).…”