Effect of organophosphates on Acarophenax lacunatus (Prostigmata: Acarophenacidae) parasitising Rhyzopertha dominica (Coleoptera: Bostrichidae)

摘要

The interaction between the organophosphate insecticides fenitrothion and piriraiphos-methyl with Acarophenax lacunatus (Cross and Krantz) (Prostigmata: Acarophenacidae), an egg parasite of the stored grain pest Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), was assessed in a range of doses for each compound. The experimental units were Petri dishes containing 25 g of whole wheat grains (13 percent m.c.) treated with insecticides and infested with 25 adults of R. dominica. Seven days after the insect infestation, mites were released at different densities per experimental unit. Four replicates were used for each combination of insecticide, dose and mite density. The number of physogastric females of A. lacunatus and egg parasitism (percent)increased with decreases in insecticide dose and increases in mite density for both organophosphates. Lower insecticide doses for fenitrothion and pirimiphos-methyl and lower mite densities led to higher instantaneous rates of increase of the mite population. Overall, lower instantaneous rates of increase of A. lacunatus were obtained with the insecticide pirimiphos-methyl. The sustained presence of the mite species in all insecticide doses suggests that this biological control agent may be used together with insecticidal applications for controlling R. dominica, but higher insecticide doses, especially of pirimiphos-methyl, retard the mite population growth. The high rates of egg parasitism obtained with the biological control agent may aid the insecticide's effect on the adult pest population, preventing outbreaks in wheat grains and making it a potential tactic for pest management of stored wheat.