Parasitoid-host endocrine relations: self-reliance or co-optation?

Area of Science:

• Insect Endocrinology
• Chemical Ecology
• Parasitoid-Host Interactions

Background:

• Juvenile hormone (JH) regulates insect development and metamorphosis.
• Parasitism by Cotesia congregata induces developmental arrest in Manduca sexta larvae.
• Elevated hemolymph JH titers are associated with parasitized host larvae.

Purpose of the Study:

• To investigate the source and identity of elevated juvenile hormone (JH) in parasitized Manduca sexta larvae.
• To determine the role of the parasitoid, Cotesia congregata, in altering host JH levels.
• To elucidate the specific JH homologs involved in maintaining host developmental arrest.

Main Methods:

• Quantification of hemolymph JH titers in parasitized and non-parasitized Manduca sexta larvae using Gas Chromatography-Mass Spectrometry (GC-MS).
• Neck ligation experiments to isolate host corpora allata from parasitoid-infected posterior tissues.
• In vitro culture of Cotesia congregata to analyze JH production.

Main Results:

• Parasitized larvae exhibited significantly higher hemolymph JH titers (up to 9.5-fold increase) compared to controls.
• GC-MS analysis revealed a shift in JH homolog dominance from JH I in controls to JH III in parasitized larvae.
• JH III was detected in the posterior hemolymph of parasitized larvae post-ligation and was the sole JH homolog produced by the parasitoid in vitro.

Conclusions:

• Cotesia congregata secretes juvenile hormone III (JH III), directly contributing to elevated JH titers in parasitized Manduca sexta larvae.
• Parasitoid-derived JH III, along with host-produced JH I and II, likely maintains larval developmental arrest.
• This study provides the first evidence of a parasitoid secreting JH III to manipulate host endocrine systems.