Discrimination of infested cotton squares by females of Anthonomus grandis Boheman (Coleoptera: Curculionidae)

Abstract

The avoidance of infested squares of Gossypium hirsutum as oviposition substrate by females ofAnthonomus grandis was studied following two approaches. First, the preference for oviposition ininfested versus non-infested squares was studied in laboratory. Second, the distribution of ovipositions byA. grandis in nature was analyzed in cotton plots from Argentina. In addition, the consequences of multipleovipositions were assessed in terms of emergence rate, adult weight and sex ratio. In the laboratory, thenumber of ovipositions was significantly higher in non-infested than in infested squares. Likewise, femaleswere found to reject infested squares more frequently than non-infested squares. In the field, ovipositionpattern fitted a uniform distribution for squares collected from the ground, while the distribution in squaressampled from the plant fitted random and uniform distributions. This suggests that oviposition decisionscould be dynamic and change with the infestation conditions. Multiple ovipositions resulted in theelimination of competing larvae between L1 and L2 instars. The weight of the individual that develops tothe adult stage was negatively affected by the level of larval competition, and the sex ratio deviated towardfemales. Our results suggest that females of A. grandis tend to avoid already infested squares. Thisbehavior would allow reducing the levels of intraspecific competition, which we also found can seriouslyaffect the development of their progeny. A deeper knowledge of the oviposition behavior of A. grandiscould contribute to developing control methods against this important cotton pest