Laboratory evaluation of the efficacy of diatomaceous earths againstPlodia interpunctella (Hübner) larvae on treated broken and unbroken maize kernels

Abstract: Inert dusts have been increasingly used to control stored-product insects, anddiatomaceous earth products are the most important of them. Their efficacy is significantlyaffected by dust origin, environmental conditions, type of cereal grains and degree of graindamage. In laboratory experiments at 24±1°C and 60±5% r.h., we conducted preliminary testingof the efficacy of two Serbian diatomaceous earth products, DE S-1 (with 79.8% of SiO2) and DES-2 (with 63.2% of SiO2) (roughly purified at the Institute of Technology of Nuclear and OtherRaw Materials, Belgrade), against L3-L4 larvae of Indian meal moth Plodia interpunctella(Hübner), and compared the results with those of the registered product Protect-Ittm (HedleyTechnologies Inc., Canada). Maize containing 14.99% broken grains and maize without anybroken grains were used in efficacy tests that employed modified methods OEPP/EPPO (2004).The Serbian dust products were tested at 0.6, 1.0 and 1.5g/kg rates, while Protect-Ittm was appliedat the recommended rate of 0.6g/kg. Lethal effects were evaluated after 7 and 14 days of larvalcontact with treated maize grains. Depending on the application rate, larval mortality after 7 daysof contact with treated broken grains was found to range: 50.0-73.3% (DE S-1), 8.3-51.7% (DES-2), and 45.0% (Protect-Ittm), while dust efficacy on treated unbroken grains was significantlyhigher: 83.3-100% (DE S-1), 81.7-98.3% (DE S-2) and 91.7% (Protect-Ittm), respectively. After14 days of larval contact with broken maize grains, the efficacy of Protect-Ittm and DE S-1applied at 1.0 and 1.5g/kg exceeded 95%. All three diatomaceous earth products achieved highefficacy in treatments of unbroken grains: 91.7-100% (DE S-1), 80.0-96.7% (DE S-2), and 100%(Protect-Ittm). The results indicate that the two tested Serbian diatomaceous earth dusts, especiallyDE S-1, have high insecticidal potential for control of Indian meal moth larvae.