Phloem-feeding insects create parasitoid-free space for caterpillars

Area of Science:

• Ecology
• Insect Ecology
• Chemical Ecology

Background:

• Keystone species significantly impact ecosystem structure and function.
• Phloem-feeding insects can alter ecological communities through plant-mediated or ant-mediated effects.
• Understanding these interactions is crucial for forest ecosystem dynamics.

Purpose of the Study:

• To investigate the keystone effects of phloem-feeding insects on caterpillar-parasitoid interactions in white oak (Quercus alba) ecosystems.
• To determine whether plant-mediated or ant-mediated mechanisms are responsible for altered interactions.
• To elucidate the role of plant volatile emissions in these ecological dynamics.

Main Methods:

• Factorial manipulation of phloem-feeding insect presence and ant access on Quercus alba branches across multiple years and sites.
• Measurement of parasitism rates of co-occurring caterpillars.
• Assessment of plant volatile compound emissions in response to herbivory and phloem-feeder presence.

Main Results:

• The presence of phloem-feeding insects completely suppressed caterpillar parasitism (0%), compared to 19.3% parasitism when phloem feeders were absent.
• Manipulation of ant access did not affect caterpillar parasitism rates, indicating a plant-mediated mechanism.
• Phloem feeders reduced concentrations of key caterpillar-induced volatile compounds emitted by the plant.

Conclusions:

• Phloem-feeding insects exert a keystone effect by eliminating caterpillar parasitism, primarily through a plant-mediated mechanism.
• The mechanism involves the suppression of plant volatile emissions, disrupting parasitoid host-location behavior.
• These findings offer novel insights into forest community dynamics and the broader ecological roles of phloem-feeding herbivores.