Cottonwood Leaf Beetle

Management of cottonwood leaf beetle, Chrysomela scripta (Coleoptera: Chrysomelidae) with a transplant soak and biorationals to conserve coccinellids

Chrysomela scripta F. (Coleoptera: Chrysomelidae) is a native defoliator of hybrid poplar cultivated for biomass, pulp, and timber. Poplars are called short-rotation woody crops because they grow quickly and are harvested every 5 to 15 years.

Adults and larvae feed on shoot terminals (LP1 0-8) (Bingaman & Hart 1992). Feeding can kill saplings and reduce tree height, diameter, and biomass (Anderson & Nelson 2002, Fang et al. 2002, Reichenbacker et al. 1996). Three to four generations occur in Minnesota and up to seven occur in the south (Oliveria and Solomon 2004).

Broad-spectrum conventional insecticides such as acephate, carbaryl, chlorpyrifos, and lambda-cyhalothrin are used to cottonwood leaf beetle, but also kill predators. Coccinellids, such as Coleomegilla maculata, Hippodamia convergens, and Harmonia axyridis consume eggs and control C. scripta after three years (USDA 1989).

Hypotheses

A novel stick soak of imidacloprid will become systemic and reduce survivorship of adult and larval C. scripta without harming coccinellids.
Foliar sprays of biorational insecticides reduce survivorship of adult and larval C. without harming coccinellids.

Methods: Stick Soak Bioassay

Soak NM6 sticks in imidacloprid (Admire 2) for 48 h: Control (0 ml/liter), 1x (3 ml/liter), 2x (6 ml/liter).
Evaluate beetle survivorship at 96 hours after exposure to imidacloprid.

Methods: Foliar Biorationals Bioassay

Spray:

Control (water)
Azadirachtin (Azatin XL)
Beauveria bassiana (Botanigard)
Bacillus thuringiensis var. tenebrionis (Novodor)
Bacillus thuringiensis var. kurstaki (Raven)
Spinosad (Conserve SC)
Imidacloprid (Admire 2)
Carbaryl (Sevin XLR Plus)

Evaluate beetle survivorship at 7 days after exposure to insecticides

Results: Stick Soak Bioassay

A novel stick soak of imidacloprid killed adult and larval C. scripta up to 10 months after treatment (Figure 1).
Coccinellids were not affected.

Results: Foliar Biorationals Bioassay

Biorational insecticides Bacillus thuringiensis var. kurstaki (Btk), B.t. var. tenebrionis (Btt), and spinosad (Spin) killed adult and larval C. scripta as well as conventional insecticides carbaryl (Carb) and imidacloprid (Imid). Azadirachtin (Azad) also killed larval C. scripta. Beauveria bassiana (Bb) did not kill beetles (Figure 2).
Coccinellids Hippodamia convergens and Harmonia axyridis were killed only by carbaryl and imidacloprid (Figure 2).

Figure 1

Figure 2

Conclusions
IPM can manage Chrysomela scripta while preserving coccinellids. A stick soak of imidacloprid during the first year of growth and biorational foliar sprays of spinosad (Conserve SC) or Bacillus thuringiensis var. tenebrionis (Novodor) starting in year three can reduce C. scripta numbers while preserving coccinellids. The novel transplant stick soak is now on an imidacloprid label for poplars.

References
Andersen, D. C. and S. M. Nelson. 2002. Effects of cottonwood leaf beetle Chrysomela scripta (Coleoptera: Chrysomelidae) on survival and growth of Fremont cottonwood (Populus fremontii) in northwest Colorado. Am. Mid. Nat. 147: 189-203.

Bingaman, B. R. and E. R. Hart. 1992. Feeding and ovipositional preferences of adult cottonwood leaf beetles (Coleoptera: Chrysomelidae) among Populus clones and leaf class ages. Environ. Entomol. 21: 508-517.

Fang, Y., L. P. Pedigo, J. P. Colletti, and E. R. Hart. 2002. Economic injury level for second-generation cottonwood leaf beetle (Coleoptera: Chrysomelidae) in two-year-old Populus. J. Econ. Entomol. 95(2): 313-316.

Oliveria, F. L and J. D. Solomon. 2004. Forest pests of North America: Cottonwood leaf beetle. http://www.forestpests.org/nursery/cwleafbeetle.html.

Reichenbacker, R. R., R. C. Schultz, and E. R. Hart. 1996. Artificial defoliation effect on Populus growth, biomass production, and total nonstructural carbohydrate concentration. Environ. Entomol. 25(3): 632-642.

(USDA) U.S. Department of Agriculture Forest Service. 1989. Insects and diseases of trees in the south: Cottonwood leaf beetle, Chrysomela scripta F. http://www.forestpests.org/southern/cottonwoodleaf.html.