A life system simulation model for improving inundative releases of the egg parasite, Trichogramma minutum against the spruce budworm

Abstract A model, based on the concept and analysis of the population life system, is described for the spruce budworm, Choristoneura fumiferana (Clemens). Four years of field data collected from northern Ontario were used in the model to simulate inundative releases of the egg parasite, Trichogramma minutum Riley, for suppression of spruce budworm populations and determine the best strategy for parasite release in terms of frequency, timing and rate of release. Hypothetical releases, either ‘single 24-h releases’, ‘single staggered releases’ or ‘double releases’, were assumed to occur from 2 to 19 days after the first spruce budworm egg masses appeared. The model predicts that, if properly timed during the oviposition of spruce budworm, ‘double releases’ and ‘single staggered releases’ of parasites can be more effective than ‘single 24-h releases’ with the same rate of release. The best timing for either type of ‘single release’ was 14 days after the first egg masses appeared. For ‘double releases’, the best timing of the first release was 12 days after the first egg masses appeared with a second release 4 days later. ‘Single staggered releases’, at 12 × 10 6 ♀ ♀ per ha, provided the best suppression of spruce budworm populations (49%) when the emergence of the parasites increased over a 5-day period from 10, 15, 20, 25 and 30% per day. The simulated results varied slightly from year to year based on mean daily temperatures in the field.