We may be looking at a banner year for yellowjackets in the western states.
Yellowjacket populations fluctuate dramatically from year to year. In the Lake Tahoe Basin area of California, we experienced very high yellowjacket populations between 1980 through 1984. Then the number of yellowjackets (and the number of nests we were treating) decreased dramatically. But in 1988, the populations rebounded to very high numbers. In 1989, we experienced a yellowjacket invasion that was so intense that the recreational sites—campgrounds, beaches etc…—were almost deserted in August and September.\
The weather conditions in California this winter and spring, 2009-2010, are very similar to the weather patterns we saw in the 1988-89 years in the Lake Tahoe area. And, my sales of ALPINE yellowjacket bait stations this year to California suppliers are running very high when compared to 2009. These factors may indicate that this year could a very large yellowjacket year for California.
I began studying yellowjacket populations in relation to weather patterns in the early 1980s. In Lake Tahoe, there appears to be a strong correlation between below normal precipitation amounts and higher yellowjacket populations. Quite simply, the lower the precipitation, the higher the yellowjacket populations.
Yellowjackets, especially the ground nesting species, thrive in drought conditions. There are many reasons for this correlation, including the fact that higher moisture levels decrease suitable areas for nests and rainy days inhibit a yellowjacket’s ability to hunt for food. In addition, the nematode parasite that attacks yellowjacket queens in the spring requires high humidity levels to survive.
Does the current drought cycle in the western states mean that California, Oregon, Washington, Idaho and Montana are in for a big yellowjacket year? Not necessarily, but it’s certainly something to keep in mind.