Dynamics of viral disease and population fluctuations in western tent caterpillars (Lepidoptera : Lasiocampidae) in southwestern British Columbia, Canada
B. Kukan et Jh. Myers, Dynamics of viral disease and population fluctuations in western tent caterpillars (Lepidoptera : Lasiocampidae) in southwestern British Columbia, Canada, ENV ENTOMOL, 28(1), 1999, pp. 44-52
Models of the dynamics of forest caterpillars and viral disease are sensiti
ve to virus persistence at low host densities. Nuclear polyhedral virus cou
ld persist in the environment on tree bark or in the soil, or by infecting
caterpillars even at low host population numbers. We monitored populations
of western tent caterpillars at 4 locations in southwestern British Columbi
a, Canada, to describe the relationship between host numbers and viral infe
ction and to determine if virus is maintained in low populations of caterpi
llar hosts. We evaluated the persistence of virus on tents. Vital infection
was detected by DNA-dot blotting of larvae and extracts from field-collect
ed tents. Although active virus persisted over winter on experimentally con
taminated tents, few tents collected from low field populations were positi
ve for viral contamination. Tents are therefore unlikely to be a source of
environmental contamination when host numbers are low. Virus was generally,
but not always present in a few larvae even in years of low host numbers.
In 2 populations the level of infection increased with host numbers, and it
remained high at the beginning of the decline in 1 population but decrease
d to a low level even at high host numbers in the other. Western tent cater
pillars at 2 mainland locations did not show a typical pattern of cyclic po
pulation fluctuation and for these the levels of viral infection did not va
ry consistently with host numbers. Presence or absence of infection was not
related to the size of the egg mass from which the family of larvae hatche
d although egg masses associated with contaminated tents tended to be small
er than those of noncontaminated tents.