Factors influencing dispersal of larval Coleomegilla maculata from the weed Acalypha ostryaefolia to sweet corn

The polyphagous predator, Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae), commonly oviposits on the native weed, Acalypha ostryaefolia Riddell (Euphorbiaceae), in and around Kentucky sweet corn fields. Cannibalism of eggs by C. maculata adults and larvae is drastically lower on A. ostryaefolia than on nearby sweet corn plants. We examined ovipositional preference of C. maculata for A. ostryaefolia plants or sweet corn plants, dispersal of larvae from A. ostryaefolia plants, capability for dispersal of larvae across bare soil (e.g., to nearby plants), ability of larvae to climb from ground level up A. ostryaefolia plants or sweet corn plants, and effect of A. ostryaefolia borders adjacent to sweet corn plots on C. maculata population density in sweet corn. The ovipositional preference study revealed that C. maculata laid more eggs on A. ostryaefolia than on corn. First-instar C. maculata that hatched from egg clusters on A. ostryaefolia dispersed predominantly by falling, rather than crawling, to the ground. Glandular trichomes on A. ostryaefolia petioles and stems apparently inhibited intraplant movement of first instars, resulting in those larvae falling directly from leaves to the ground. Some first instars were capable of moving at least 8 m across bare soil in 24 h. From the ground, significantly more first instars climbed sweet corn plants than climbed A. ostryaefolia plants. Significantly more larvae were present in sweet corn plots bordered by A. ostryaefolia plants than in sweet corn plots without an A. ostryaefolia border. These findings show that physical attributes of companion plants can significantly influence natural enemy populations on crop plants by affecting interplant dispersal of natural enemies.