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
& 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
-
NM6 sticks were soaked in
imidacloprid (Admire 2) for 48 h: Control (0 ml/liter), 1x (3 ml/liter),
2x (6 ml/liter) and plant in the greenhouse.
-
Beetle survivorship was
evaluated for 10 months after 96-hour exposure to leaves from imidacloprid-treated
and untreated plants.
Methods: Foliar
Biorationals Bioassay
-
Plants were sprayed and allowed
to dry:
-
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)
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-
Beetle survivorship was
evaluated for 7 days after exposure to leaves from sprayed plants.
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).
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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.
Published here:
Tenczar, E. G., and V. A. Krischik. 2006. Management of cottonwood leaf
beetle (Coleoptera: Chrysomelidae) with a novel transplant soak and
biorational insecticides to conserve coccinellid beetles. J. Econ. Entomol.
99(1): 102-108. |
