Western pine beetle voltinism in a changing California climate

Recent hot droughts in California resulted ponderosa pine (Pinus ponderosa) mortality attributed to drought and western beetle (WPB, Dendroctonus brevicomis). While alone can cause tree death, direct warming effects on WPB are a contributing factor. Research generation timing (voltinism), however, is lacking. We monitored attacks adult emergence at two sites developed degree-day model from field-observed data. Historical, contemporary, future temperatures for several were used with the examine trends voltinism. Field data showed single summer an overwinter northern site. As increased beyond 1900–1980 averages, predicted number of full partial generations by 2021 had ~2 annual (one one overwinter) historically ~2.3 ~3.2 warmer sites. Historical contemporary suggest winter was not sufficient additional overwinter. Instead, increases driven fall temperatures. Unconstrained will be limited complex, but well understood, thermal adaptations. Increased knowledge temperature-driven population growth improve forest vegetation models aimed predicting changing climate.