Dynamics of Nocturnal Activity of Moths in the Heliothis Complex (Lepidoptera: Noctuidae) in Cotton

Abstract

Nocturnal activity of adult Helicoverpa zea (Boddie) and Heliothis virescens (F.) was monitored in cotton, from the pinhead square to open boll stage, in the Delta region of Mississippi. Samples were taken at hourly intervals by hand capture and pheromone traps and through the night by ultraviolet blacklight traps and compared with egg counts obtained from whole-plant inspection made the following day. H. virescens was the dominant species in all sampling (>80% of all trapped males, >98% of all hand captured adults, and >98% of all egg counts), with the exception of blacklight traps (33% of all adults trapped). Low average adult fat body ratings (<2) and low average number of spermatophores in females, together with low oviposition rates, indicate that H. zea was not a predominant resident during the sampling period (generations F2-F4). For H. virescens , hand captures of both males and females were highly correlated with egg counts ( r = 0.8888; P < 0.0001). Correlation between H. virescens moths caught in pheromone traps and those caught by hand (and egg counts) were highest when the number caught in traps was compared with the number caught by hand 4 d previously ( r = 0.5800, P < 0.0001). No association was found between captures in blacklight traps and captures by hand (or egg counts) for either species. Over 70% of all H. virescens caught by pheromone traps occurred after midnight, 64% of all H. virescens females caught by hand occurred before midnight, and hand-captured males were nearly equally divided before and after midnight. Over the season, during each generation, trapped and hand-captured males showed a tendency to reach peak numbers in later intervals. For both sexes, movement was most frequently observed during early intervals (2000-2300 hours CDST), with a lull in activity around midnight, followed by a high frequency of mating during later intervals (0100-0300 hours). The highest frequency of mating females was found during the sixth interval (0145-0245 hours), coincident with a dip in trap capture frequency. Trap capture frequency rose to a second peak during interval 7 (0300-0400 hours), coincident with the highest frequency of mating males. The consistency of the observed nocturnal patterns (in-field and trap), together with other studies showing similar results, lead to the conclusion that knowledge of nightly temporal frequency of trap captures may provide critical information for more accurate prediction of field population development than is currently possible with daily summary trap data alone.