Dispersion of Acarophenax lacunatus (Cross & Krantz) (Prostigmata: Acarophenacidae) in stored wheat, under artificial conditions

Ability to disperse is fundamental for a successful natural enemy in a stored grain environment. The objective of the present work was to assess whether the mite Acarophenax lacunatus (Cross & Krantz) disperses in a grain mass to locate its host Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae). The experiment was based on the release of physogastric females of A. lacunatus on the surface of glass containers containing Petri dishes with 20 adults of R. dominica at different depths (4, 8, 12, 16 and 20 cm). The Petri dishes were covered with voil to prevent insect escape. Dispersion of the progeny of these physogastric females was assessed 10, 20 and 30 days after the beginning of the experiment. The mites were able to disperse and they were observed at every depth and at every period of assessment. Nonetheless, the number of A. lacunatus decreased with the increasing depth, with highest values observed at the lowest depths after 20 and 30 days of storage. It is possible that evaluations conducted in periods longer than 30 days of the parasite release could demonstrate an increase in parasitism at higher depths. The results indicated that A. lacunatus actively disperse for up to 20 cm on its own, without the assistance of its host for phoresy.