Residual efficacy of the insecticide deltamethrin, an EC formulation
containing 25 g/L AI + 225 g/L PBO (piperonyl butoxide synergist), against
lab populations of Sitophilus oryzae, Rhyzopertha dominica, Tribolium
castaneum and Sitotroga cerealella was investigated in the laboratory by
applying product water solutions (0.25 mg AI/kg) to wheat grain (at 25?1?C
and 60?5% r.h.). Adult mortality on 0, 7, 14 and 30 days old deposits was
estimated after 2, 7 and 14 days of exposure to treated wheat grain and
additional 7 days of recovery. Progeny reduction (PR, %) was also assessed.
After 2 days of exposure to deposits of all ages, deltamethrin caused only
0-10% mortality of coleopterans (up to 37% after the recovery period) and
23-30% of S. cerealella, while mortality before and after recovery from 14
days of exposure was 95-50% for S. oryzae, 97-100% for R. dominica, 99-100%
for T. castaneum and 100% for S. cerealella. Progeny production of S. oryzae
was highest after parents contacted with 14 days old deposit of deltamethrin
(PR, 76%), and lowest after contact with fresh deposit (PR, 95%), while R.
dominica and T. castaneum had no progeny on any deltamethrin deposit age in
wheat (PR, 100%), and S. cerealella had only a very low progeny (PR, 99%).
The results showed that the synergised deltamethrin, applied at 0.25 mg/kg in
wheat grain, is a highly effective insecticide for storedproduct insect
control, while a higher dose is required for successful residual control of
S. oryzae.