Submitted to: American Bee Journal
Publication Type: Trade journal
Publication Acceptance Date: 6/10/2005
Publication Date: 8/20/2005
Citation: DeGrandi-Hoffman, G., Curry. R. Simulated population dynamics of Varroa mites in honey bee colonies: Part II - What the VARROAPOP model reveals. Amer. Bee J. 2005. Vol. 145(8): 629-632. Interpretive Summary: Simulations with a mathematical model (VARROAPOP) were conducted to predict colony population growth with and without Varroa under southwest and temperate weather conditions. The program also was used to determine the effectiveness of miticide applications made at various times of the year. Effectiveness of the miticide was determined by the length of time the colony survived following the miticide application. Honey bee populations were larger under southwestern weather because brood rearing occurs throughout the year and at higher rates during the early spring and fall than under temperate conditions. The Varroa population also grows at a faster rate under southwestern compared with temperate weather. The model predicts that miticides applied in the late summer provide the best chances for the survival of heavily infested colonies. This is because late summer applications reduce the period when worker brood is multiply infested by Varroa. Multiply infested worker cells result in reduced longevity of adult workers. If miticide applications are delayed until September or October, most of the adult workers comprising the overwintering colony population have reduced longevity. The model also predicts that mite populations treated with mitidices in the spring will recover by autumn to levels similar to those in untreated colonies. This is because in the treated colonies the surviving mites infest drone brood at lower numbers per cell and this maximizes their reproductive and population growth rates.
Technical Abstract: The VARROAPOP program was used to predict colony population growth with and without Varroa mites under southwestern and temperate weather conditions. Both honey bee and Varroa populations build faster under southwestern weather conditions compared with temperate weather. The VARROAPOP program predicts that the most effective time to apply miticides is in the late summer. The chances of a colony that is severely infested with Varroa surviving the winter decreases as miticide applications are delayed into the fall. The reason is that the period when worker brood is multiply infested by Varroa is reduced by earlier miticide applications. Workers that develop in cells multiply infested with Varroa have reduced lifespans as adults. When miticides are applied in the late summer, the worker population that comprise the majority of the winter cluster are reared in a mite-free colony. VARROAPOP also predicts that Varroa populations that were reduced by miticides applied in the spring will recover to the same levels as untreated colonies by the fall. The mite populations in treated colonies grow at a faster rate than in untreated colonies primarily because they singly infest drone brood which maximizes the number of offspring a foundress mite can produce.