Persistence and efficacy of Metarhizium anisopliae (Metschnikoff) Sorokin (Deuteromycotina: Hyphomycetes) and diatomaceous earth against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) on wheat and maize

Abstract

Wheat and maize were treated with 8×106 and 8×108 conidia/kg of the entomopathogenic fungus Metarhizium anisopliae (Metschnikoff) Sorokin, alone and in combination with 250 ppm Diatomaceous Earth (DE). Bioassays were conducted after application and monthly for 5 months using adult Sitophilus oryzae (L) and Rhyzopertha dominica (F.). Both treated grains and the bioassay samples were held at 27±1 °C and 65±5% r.h. Mortality assessments were made at 7 and 14 d, and after the 14 d counts all adults were removed and the samples incubated at the same environmental conditions for 60 d to record progeny production. Mortality of S. oryzae exposed for 7 d on both grains decreased during the 5-month period, however, maximum mortality usually occurred in the combination of the highest fungal rate with the DE. Mortality of S. oryzae was generally lower in maize than in wheat. Mortality of R. dominica in both grains was generally greater than mortality observed for S. oryzae. Progeny production of S. oryzae increased gradually during the 5 months, but this increase varied depending on the treatment. Similar results were noted for R. dominica with generally lower progeny production compared with S. oryzae.