Competing beetles attract egg laying in a hawkmoth

Area of Science:

• Ecology
• Chemical Ecology
• Behavioral Ecology

Background:

• Plant-insect interactions are complex, involving multiple species and trophic levels.
• Herbivore infestation alters plant volatile emissions, influencing subsequent insect behavior.
• The molecular and olfactory mechanisms driving these altered insect preferences are largely unknown.

Purpose of the Study:

• To investigate the oviposition preferences of tobacco hawkmoths (Manduca sexta) on Jimson weed (Datura wrightii) infested by the three-lined potato beetle (Lema daturaphila).
• To elucidate the olfactory mechanisms and volatile compounds mediating these host plant selection behaviors.
• To determine the fitness consequences of this interspecific interaction for the moth offspring.

Main Methods:

• Observed oviposition choices of Manduca sexta on Datura wrightii with and without Lema daturaphila infestation.
• Analyzed volatile organic compounds (VOCs) emitted by infested and uninfested plants.
• Conducted behavioral assays using synthetic volatiles and electrophysiology (single-sensillum recordings) to identify olfactory receptors involved.
• Performed larval development studies to assess fitness trade-offs.

Main Results:

• Manduca sexta females preferentially oviposit on Datura wrightii infested by Lema daturaphila.
• Moth larvae exhibit slower development when feeding on beetle-infested plants due to interspecific competition.
• The parasitoid wasp Cotesia congregata (a predator of M. sexta) avoids plants infested by both herbivores.
• The volatile compound α-copaene, emitted by beetle-infested plants, plays a role in mediating moth preference.
• Odorant receptor Or35 in Manduca sexta is involved in detecting α-copaene.

Conclusions:

• Female Manduca sexta prioritize enemy-reduced space over direct larval food competition when selecting oviposition sites.
• This trade-off, mediated by olfactory cues like α-copaene detected by Or35, provides a net benefit for offspring survival and fitness.
• Demonstrates a sophisticated multi-trophic interaction where herbivores manipulate host plant volatiles to gain an advantage against their own natural enemies.