An Egg Parasitoid Efficiently Exploits Cues From a Coevolved Host But Not Those From a Novel Host

Area of Science:

• Ecology
• Entomology
• Biological Control

Background:

• Egg parasitoids rely on host-associated cues for host selection, impacting parasitoid specificity.
• Trissolcus japonicus is an effective parasitoid of Halyomorpha halys, a significant agricultural pest, and has been introduced to North America and Europe.
• Trissolcus japonicus can develop on Podisus maculiventris, a non-native predatory stink bug, raising concerns about non-target effects.

Purpose of the Study:

• To test the hypothesis that naïve Trissolcus japonicus females utilize cues from their coevolved host (Halyomorpha halys) but not from a novel host (Podisus maculiventris).
• To evaluate the role of host-associated volatiles, including plant volatiles and adult/egg odors, in the host-location behavior of Trissolcus japonicus.
• To assess the implications of host-specific cue exploitation for the biological control potential and risk assessment of Trissolcus japonicus.

Main Methods:

• Utilized Y-tube olfactometers to test the responses of naïve Trissolcus japonicus females to volatiles from tomato plants treated with Halyomorpha halys or Podisus maculiventris.
• Assessed responses to volatiles emitted by Halyomorpha halys and Podisus maculiventris eggs, gravid females, and mature males.
• Maintained Trissolcus japonicus on its coevolved host, Halyomorpha halys, prior to experiments to ensure naïve females.

Main Results:

• Trissolcus japonicus females preferred volatiles from tomato plants exposed to Halyomorpha halys over clean plants, indicating attraction to indirect plant defenses.
• Parasitoid females were attracted to cues from adult Halyomorpha halys (males and females) but not to Halyomorpha halys eggs.
• Naïve Trissolcus japonicus females showed no attraction to any cues associated with Podisus maculiventris, despite its suitability for development.

Conclusions:

• Naïve Trissolcus japonicus females exhibit specific responses to cues from their coevolved host, Halyomorpha halys, but not from the non-target host, Podisus maculiventris.
• The lack of response to Podisus maculiventris cues may limit the field-level parasitism of this non-target host, potentially reducing risks in biological control.
• The study's methodology simulates natural host-location processes and supports its use in host specificity testing for biological control risk assessment.