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Submitted to: International Symposium on Biological Control of Arthropods
Publication Type: Proceedings Publication Acceptance Date: 3/1/2002 Publication Date: 1/3/2003 Citation: Tillman, P.G. 2003. Toxicity of indoxacarb to the tarnished plant bug, Lygus lineolaris (Hemiptera:Miridae), and the big-eyed bug, Geocoris punctipes (Hemiptera: Lygaeidae). International Symposium on Biological Control of Arthropods. January 14-18, 2002. Honolulu, Hawaii. USDA, Forest Health Technology Enterprise Team, Morgantown WV. p 296-305. Interpretive Summary: The toxicity of Steward, an insecticide created for control of the tarnished plant bug, was determined for this cotton pest and the big-eyed bug, a predator of cotton pests. Both insects responded similarly to Steward when applied to their bodies, when they walked on residues, and when they fed on cotton leaves with residues. Walking on residues of Steward did not kill either insect species. However, feeding on cotton leaves with residues of Steward resulted in high mortality for both insects. Feeding on water-washed plants resulted in lower mortality than that observed for unwashed plants, and mortality declined even more dramatically after a detergent rinse, indicating that much of the active ingredient of the insecticide probably was on the surface of cotton leaves. High humidity resulted in higher mortality for both species. When female big-eyed bugs ate prey treated with Steward, a reduction in feeding lowered the rate of mortality for this predator. Technical Abstract: The toxicity of Steward, a formulation of indoxacarb, was studied for the tarnished plant bug [Lygus lineolaris (Palisot de Beauvois)], a pest of cotton, and the big-eyed insect [Geocoris punctipes (Say)], a predator of pests in cotton. Both insects responded similarly to Steward in topical, tarsal contact, and feeding toxicity studies. The topical LD50 for Steward was c 35 ng of active ingredient per insect for both insects. Prolonged tarsal contact with dry Steward residues did not result in mortality for either insect species. However, both species were susceptible to the insecticide via feeding through dried residues of Steward. Feeding on water-washed plants resulted in lower mortality than that observed for unwashed plants, and toxicity declined even more dramatically after a detergent rinse indicating that much of the active ingredient of the insecticide probably resides on the cotton's surface or in the waxy cuticle. These results were corroborated by HPLC-mass spectrometry measurements of indoxacarb residues on the plants. Greater mortality for both species was observed in a higher relative humidity environment. When female G punctipes ate Steward-treated H zea eggs, there was significant toxicity. However, only c 15% of the females consumed Steward-treated eggs, and in fact a significant diminution of feeding was observed in response to the insecticide for the rest of the females. In conclusion, a major route of intoxication of L. lineolaris in Steward-treated cotton fields thus appears to be via oral, and not cuticular, uptake of Steward residues from treated cotton. |
