Variable concentration of soil-applied insecticides in potato over time: implications for management of Leptinotarsa decemlineata.
BACKGROUND
Select populations of Colorado potato beetle, Leptinotarsa decemlineata, in Wisconsin have recently become resistant to soil-applied neonicotinoids in potato. Sublethal insecticide concentrations persisting in foliage through the growing season may select for resistance over successive years of use. Over the 2 years of this study, the aim was to document the in-plant insecticide concentrations over time that result from four different types of soil-applied insecticide delivery for thiamethoxam and imidacloprid in potato, and to measure the impact upon L. decemlineata populations following treatments. After plant emergence, insect life stages were counted and plant tissue was assayed weekly for nine consecutive weeks using ELISA.


RESULTS
Peak concentration of both imidacloprid and thiamethoxam occurred in the first sample week following plant emergence. The average concentration of both insecticides dissipated sharply over time as the plant canopy expanded 50 days after planting in all delivery treatments. Both insecticides were detected at low levels during the later weeks of the study. Among-plant concentrations of both neonicotinoids were highly variable throughout the season. Populations of L. decemlineata continued to develop and reproduce throughout the period of declining insecticide concentrations.


CONCLUSIONS
Sublethal, chronic exposure to soil-applied systemic insecticides resulting from these delivery methods may accelerate selection for resistant insects in potato.
Department of Entomology, Cornell University, New York State Agricultural Experiment Station, Geneva, NY, USA.
Anders S
AS
Huseth
Joliene
J
Lindholm
Carol L
CL
Groves
Russell L
RL
Groves
D000818:Animals; D001517:Coleoptera / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D007093:Imidazoles / Q000032:analysis / Q000494:pharmacology; D007300:Insect Control / Q000379:methods*; D007305:Insecticide Resistance / Q000187:drug effects; D007306:Insecticides / Q000032:analysis* / Q000494:pharmacology; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000032:analysis / Q000494:pharmacology; D010078:Oxazines / Q000032:analysis / Q000494:pharmacology; D010573:Pesticide Residues / Q000032:analysis* / Q000494:pharmacology; D012987:Soil / Q000737:chemistry; D011198:Solanum tuberosum / Q000737:chemistry*; D000077922:Thiamethoxam; D013844:Thiazoles / Q000032:analysis / Q000494:pharmacology; D014922:Wisconsin
D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; D010078:Oxazines; D010573:Pesticide Residues; D012987:Soil; D013844:Thiazoles; C082359:imidacloprid; D000077922:Thiamethoxam
Colorado potato beetle; imidacloprid; insecticide resistance management; systemic insecticides; thiamethoxam