In the Ecology and Evolution paper, Hsieh, Perfecto and their colleagues show that female lady beetlesespecially pregnant onesdetect the phorid-alert pheromone and take advantage of the ensuing lull in activity to search out safe egg-deposition sites with plenty of food for their offspring. Interestingly, male beetles did not respond to any of the ant pheromones.
For the study, beetles, ants and phorid flies were collected from an organic coffee plantation in the southern part of the state of Chiapas, Mexico, or were reared in the laboratory after field collection from the same site. The insects were placed in a multi-chambered apparatus called an olfactometer, which is used to measure an organism's sensitivity to various odors.
In addition to several olfactometer tests, an egg-deposition experiment was conducted. Pregnant lady beetles were placed in a one-liter container holding a coffee branch with four to six leaves infected with scale insects, 40 Azteca worker ants, and two or three phorid flies. After 24 hours, the coffee branch was removed and examined under a microscope for beetle eggs.
Results of the various tests support the hypothesis that female beetles use the phorid-alert ant pheromone to exploit low ant-activity periods and to locate sites where eggs can be hidden and protected against ant predation after ants resume their normal activity levels.
The authors suggest that such complex interactions may be common in nature, "and their uncommon occurrence in the literature is the product of investigators failing to search for them in the first place."
The results have important implications for the management of the scale insect on coffee plantations. The findings suggest that the conservation of Azteca ants, rather than their elimination, is the best management option, Perfecto said.
"This is counterintuitive because the ants protect the scale insects," Perfecto said. "However, th
|Contact: Jim Erickson|
University of Michigan