Evolution of critical day length for diapause induction enables range expansion of Diorhabda carinulata, a biological control agent against tamarisk (Tamarix spp.)

Abstract

In classical weed biological control, small collections of arthropods are made from one or a few sites in the native range of the target plant and are introduced to suppress the plant where it has become invasive, often across a wide geographic range. Ecological mismatches in the new range are likely, and success using the biocontrol agent may depend on postrelease evolution of beneficial life history traits. In this study, we measure the evolution of critical day length for diapause induction (day length at which 50% of the population enters dormancy), in a beetle (Diorhabda carinulata) introduced into North America from China to control an exotic shrub, Tamarix spp. Beetle populations were sampled from four sites in North America 7 years after introduction, and critical day length was shown to have declined, forming a cline over a latitudinal gradient At one field site, decreased critical day length was correlated with 16 additional days of reproductive activity, resulting in a closer match between beetle life history and the phenology of Tamarix. These findings indicate an enhanced efficacy and an increasingly wider range for D. carinulata in Tamarix control.

Keywords: adaptation; biocontrol; life history; phenology evolution; photoperiodism.

Figure 1

Map of the western United States showing D. carinulata collection locations in Lovell, Wyoming, Lovelock, Nevada, Pueblo, Colorado, and Artesia, New Mexico with latitudes shown next to each collection location.

Figure 2

Diapause incidence in the field at the Pueblo, Colorado site during the summer of 2008. The 2003 values are from Bean et al. 2007a and are shown for comparison. The population reached 50% diapause on ordinal day 223 (August 10, 2008), while in 2003, the population reached 50% diapause on day 207 (July 26).

Figure 3

The relationship between CDL measured under three temperature regimes, and latitude at the four field sites in North America. For constant 25°C, y = 0.0388x + 13.392, R² = 0.997; for a thermoperiod 30–20°C, y = 0.0386x + 13.257, R² = 0.8011; for a thermoperiod 35–15°C, y = 0.058x + 12.064, R² = 0.7246.