The push-pull intercrop Desmodium does not repel, but intercepts and kills pests.

Area of Science:

• Agricultural Science
• Ecology
• Entomology

Background:

• The push-pull intercropping system uses a repellent plant (push) and an attractive plant (pull) to control pests in maize.
• This strategy was thought to work by repelling adult pests with volatile chemicals released by the intercrop, commonly Desmodium spp.

Purpose of the Study:

• To investigate the mechanism behind the push-pull strategy's effectiveness against lepidopteran pests in maize.
• To determine if volatile terpenoids are the primary deterrent in the Desmodium-maize intercropping system.

Main Methods:

• Analysis of volatile compounds released by Desmodium in various conditions.
• Oviposition choice tests using the invasive pest Spodoptera frugiperda in a wind tunnel.
• Larval survival and development assays on Desmodium plants.

Main Results:

• Volatile terpenoids were not detected in Desmodium headspace, and adult moths showed no preference for maize with or without Desmodium odor.
• Neonate larvae preferred Desmodium over maize but did not survive, with older larvae being impaled by silica-fortified trichomes.
• Desmodium appears to intercept and kill dispersing larvae rather than deterring adult pests.

Conclusions:

• The push-pull strategy's pest control mechanism relies on larval interception by Desmodium, not adult deterrence via volatile compounds.
• Understanding this mechanism is crucial for improving the push-pull system and applying the concept to other cropping systems.