Resistance and physiological differences in the rice weevil Sitophilus oryzae (L.) (Coleoptera: Curculionidae) exposed to diatomaceous earth

After 4.5 years of selection to diatomaceous earth (DE), the DE-exposed (DE-tolerant) Sitophilus oryzae (L) adults were approximatlely 10 times more tolerant of DE than the unselected (DE-susceptible) strain. DE-susceptible and DE-tolerant S. oryzae adults were compared for water loss, speed of movement and progeny production. For all the tests, the diatomaceous earth Protect-It (TM) was used at the ratio of 0.3 g/kg wheat and exposed for 7 days. Tolerant strains lost significantly less water when exposed to DE-treated grain and moved more quickly through grain. DE-tolerant S. oryzae produced less progeny. The speed of movement and activity in Petri-dishes were different from the movement through grain. If this level of increased tolerance towards exposure to DE was present in insect populations found in commercial stores, it would probably cause control failures. However, if the tolerant species produced fewer offspring, as in the strain studied, tolerant strains would probably diminish with time if not exposed to DE.