Laboratory and Field Tests of Insecticides against Douglas Fir Seed Wasp (Megastigmus spermotrophus Wachtl).

Tests were made to select insecticides which would kill adult seed wasps in crowns of cone-bearing Douglas fir trees. In the laboratory, gamma BHC, malathion and diazinon were found to be active against females. In further tests, on males and females, gamma BHC and malathion were active when the insects were allowed contact with treated surfaces; fenitrothion was less active. The effectiveness of gamma BHC was partly due to fumigant action whereas malathion and fenitrothion had no fumigant effect. In separate field experiments between 1962 and 1966 in Kent and Herefordshire, gamma BHC and fenitrothion gave no control but malathion gave good control. In 1968, trees in Kent to which malathion was applied three times at 10-day intervals during June had about 13 per cent infestation of potentially sound seed, when assessed in September, compared with about 45 per cent infestation on unsprayed trees. Malathion plus gamma BHC did not further reduce infestation. [ABSTRACT FROM AUTHOR]