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The toxic effects of direct pesticide exposure for a nontarget weed‐dwelling chrysomelid beetle ( Gastrophysa polygoni ) in cereals
Author(s) -
Kjaer Christian,
Jepson Paul C.
Publication year - 1995
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.5620140610
Subject(s) - convolvulus , pesticide , dimethoate , weed , biology , polygonum , aerial application , toxicology , crop , population , agronomy , interception , pest analysis , horticulture , ecology , demography , sociology
Direct insecticide deposition on adults of the chrysomelid beetle Gastrophysa polygoni L. was measured by use of fluorescent spray tracer. The beetles captured 1 .3‐to 2.5–fold the spray volume of an equivalent area of weed leaf surface. This disproportionate rate of exposure declined down through the crop canopy toward the ground. Spray deposition was measured for insects placed on both the upper and the lower surfaces of Polygonum convolvulus L. leaves within winter wheat crop canopies. The upper‐to‐lower‐surface deposition ratio was 2.3 irrespective of the position of the leaf in the crop canopy. The mortality of adult G. polygoni exposed to pesticides on their host plant was estimated, based on measurements of spray deposition on insects in different positions, the laboratory dose‐response relationship for dimethoate, and the distribution pattern of adults on the host plant measured in the laboratory. At full recommended field rate (280 g ha −1 ) an expected 40.7% of the adult population would die as a result of direct exposure to dimethoate. The mortalities on specific positions on the plant ranged between zero and 76.7%. To reduce predicted mortality to a level of 10%, it would be necessary to reduce field rate to 50% according to these calculations. Those individuals surviving the dimethoate treatment had a reduced fertility, whereas the egg viability was unaffected.