|Tillman, Patricia - Glynn|
Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2001
Publication Date: 12/1/2001
Citation: Tillman, P.G., Hammes, G.G., Sacher, M., Connair, M., Brady, E.A., Wing, K.D. 2001. Toxicity of a formulation of the insecticide indoxacarb to the tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae), and the big-eyed bug, Geocoris punctipes (Hemiptera: Lygaeidae). Pest Management Science. 58:92-100. Interpretive Summary: The tarnished plant bug is an important pest in cotton. The big-eyed bug is a predator of many prey species including tobacco budworm and corn earworm eggs, but it also can feed on plants. StewardTM is a highly effective insecticide against the tarnished plant bug and may be a new tool in an integrated pest management (IPM) program for this pest in cotton. Since the tarnished plant bug and big-eyed bug are both sucking insects an can occur in cotton fields concurrently, selectivity of StewardTM with respect to these two insects is an important issue in an IPM program. Toxicity of this insecticide to the tarnished plant bug and the big-eyed bug was studied. Steward was toxic to both insects when the insecticide was topically applied or when they fed on treated plants. However, neither were susceptible when walking on treated leaves. Female big-eyed bugs avoided eating eggs treated with this insecticide. Thus, feeding behavior, ,and not differential susceptibility, may be responsible for survival of th big-eyed bug in StewardTM treated fields. These results are critical to understand the attributes of this selective new insecticide in cotton IPM.
Technical Abstract: StewardTM is a suspensible concentrate formulation of indoxacarb, a new oxadiazine insecticide that has shown outstanding field insecticidal activity. Toxicity of this formulation of indoxacarb to the tarnished plant bug Lygus lineolaris (Palisot de Beauvois) and the big-eyed bug Geocoris punctipes (Say) was studied. Both insect species responded very similarly to indoxacarb in topical, tarsal contact, and plant feeding toxicity studies. The topical LD50 for indoxacarb was ca. 35 ng of indoxacarb per insect for both species. Prolonged tarsal contact with dry indoxacarb residues did not result in mortality for either insect species. However, both species were susceptible to feeding through dried residues of indoxacarb after spraying on young cotton plants. 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 indoxacarb active ingredient 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. Higher levels of accumulated indoxacarb and its active metabolite were detected in dead G. punctipes than L. lineolaris after feeding on sprayed, unwashed plants. However, low mortality occurred when female G. punctipes fed on eggs treated with indoxacarb. The mechanisms for selectivity/safety for G. punctipes are currently under investigation and may be associated with differential feeding behavior.