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Description

Abstract

This paper is a historical account of the experiments and observations on the population dynamics of western tent caterpillars, Malacosoma californicum pluviale, beginning in the 1975 through 2025. It contains figures of population trends and characteristics of the populations that vary with population density to show that infection by Mcplnucleopolyhedrovirus (extrinsic factor) and changes in fecundity and early larval survival (tent size) (intrinsic factors) relate to the population change. 

Methods - Myers_Cory_tent_caterpillar_Gulf_Islands_population_data.csv

Since 1975, tents were counted each May on the 7 ha Mandarte Island by following a set path around the whole island and scanning for tents on all the vegetation we could see using binoculars. Over the next 10 years additional sites on other islands and locations were identified and defined areas were monitored. On Galiano Island the main site is an approximately one kilometer section of road  A second site on Galiano Island is at Montague Harbour where the host trees are primarily domestic apples, Malus domestica, and wild rose. On Saturna Island, the site is a grassy area surrounded by red alder trees. The Westham site is an open field along a slough and a dyke extending westward toward the Strait of Georgia. Crab apple (Malus diversifolia) and alders are the dominant host trees. Alders are also the dominant host trees on Cypress Mountain, where monitoring comprises three sites along the road up the mountain.

Methods - Myers_Cory_tent_caterpillar_Galiano_population_data.csv

In addition to counting the number of WTC tents annually, we monitored changes in fecundity (number of eggs per mass) and early larval survival as indicated by tent size (maximum length x width) when the larvae were in the fourth instar. In 1990, we began monitoring the levels of infection by McplNPV using DNA analysis (Kukan and Myers 1997). Beginning in 1999, NPV infection in all sites was estimated by collecting samples of 10 fourth instar larvae per tent (family) and rearing them on alder leaves in the laboratory until one larva died of viral infection or pupation occurred. The number of parasitoids emerging from the larval samples was also recorded.