EFFECTIVENESS OF ACCUMULATED HEAT UNITS ON POPULATION FLUCTUATION OF SPINY BOLLWORM AND ASSOCIATED PREDATORS IN COTTON AND MAIZE FIELDS

The seasonal fluctuation of the spiny bollworm (SBW), moths, larvae and associated common predators in relation to accumulated heat units, were studied on cotton, Gossypium barbadense, variety Giza 86 and maize, Zea maize (Single cross, 3062), in Gharbia Governorate during two successive seasons, 2007and 2008. Results revealed that the population of male moths occurring five and four peaks for the two cotton seasons, respectively. The larval infestation of SBW on cotton showed up three peaks each successive cotton season. The average number of larvae at the second peak had low average number than the first and third peaks. On the other hand, the larval infestation of SBW on maize occurred in one peak during the appearance of maize flowers male (tassel) and female (silk) and growing ears. The peak of larval infestation on the maize was more than the second peak in the cotton with about five times. Common predators on cotton occurred in three and two peaks during the two seasons, respectively, while on maize, it occurred in two peaks/season. The population of common predators in the maize was lower than in the cotton fields. Regression values between accumulated heat units as independent factor and SBW male moths, larval infestation and common predators in cotton or maize as dependent factors revealed highly significant during the two seasons. The obverse r2 values ranged between 0.4883 and 0.9730. The same trend was found between accumulated SBW male moths and larval infestation in cotton. The obverse r2 values ranged between 0.7078 and 0.9182. Also, the relationships between larval infestations in cotton or maize and associated common predators were highly significant. The obverse r2 values ranged between 0.3875 and 0.9864. General revealed that the accumulated heat units, captured male moths in pheromone traps can be used to predict larval infestation in cotton and maize crops.