Distribution of 32P in Laboratory Colonies of Solenopsis invicta (Hymenoptera: Formicidae) After Feeding on Labeled Heliothis zea (Lepidoptera: Noctuidae) Eggs: An Explanation of Discrepancies Encountered in Field Predation Experiments

Abstract

Factors responsible for low recovery rates of radioactive Solenopsis invicta Buren following placement of 32P-labeled Heliothis zea (Boddie) eggs on cotton in field predation tests were investigated using laboratory colonies of the ants. S. invicta workers became radioactive while handling labeled eggs by rupturing the egg chorion or by picking up labeled substances present on the surface of eggs. Foragers that removed the eggs from the plants picked up significantly more of the label than did workers that were sampled from the colonies between 12 and 72 h after egg introduction. Percentage of workers that became labeled over time was much lower with the solid live food than in other studies that used powdered food sources. Problems in finding labeled ants in the field may have been associated with low mean levels of 32P per ant, together with difficulty in locating and isolating labeled ants from the population. Results indicate that egg predation rates estimated from counts per minute per predator have high variability, and suggest fairly large errors in estimates of eggs consumed per ant. Use of recovery rates of labeled predators to improve estimation of predation rates is discussed.