Interception of Native Male Tobacco Budworm by Barriers of Released Laboratory-Reared Sterile Females

Releases of as few as 1400 virgin female tobacco budworms, Heliothis virescens (F.), sterilized with CO60 produced a 322-m barrier zone around a given area by intercepting and copulating with 91% of the native males. The released females dispersed well over the zone, positioned themselves on the upper portions of the canopy of various types of plants, and began calling (secreting pheromone) at ca. 2 h after sundown. No males passed through the barrier before 3 AM (COT), when the supply of available females (unmated) in the barrier had been depleted. The mating response of males inside and outside the barrier was compared by placing clipped-wing females on mating tables. One-day-old females appeared to form a better barrier than 2- to 5-day-old females stored at 13.3°C. Female barriers might be used in behavioral studies. Encapsulated sex pheromones or sterile hybrids might be substituted for barrier females in population suppression of the tobacco budworm.