Tomato Chemical Defenses Intensify Corn Earworm (Helicoverpa zea) Mortality from Opportunistic Bacterial Pathogens

Area of Science:

• Plant-insect interactions
• Chemical ecology
• Microbial pathogenesis

Background:

• Insect herbivores contend with plant defenses and microbial pathogens.
• Plant defenses can be induced upon insect attack.
• Gut microbes can exacerbate host insect vulnerability.

Purpose of the Study:

• To investigate the synergistic effects of tomato plant defenses and Serratia marcescens on corn earworm (Helicoverpa zea) mortality.
• To determine if induced plant defenses enhance the impact of an enteric bacterium on insect survival.

Main Methods:

• Bioassays using different tomato cultivars, including methyl jasmonate-induced treatments.
• Oral inoculation of Helicoverpa zea larvae with Serratia marcescens.
• Analysis of larval mortality, bacterial load in hemolymph, and polyphenol oxidase activity.

Main Results:

• Serratia marcescens alone caused >50% mortality in larvae.
• Induced tomato defenses combined with S. marcescens resulted in >95% larval mortality.
• Polyphenol oxidase activity in tomato mutants correlated with increased S. marcescens-mediated mortality.
• Bacterial load in hemolymph increased with induced plant defenses.

Conclusions:

• Plant chemical defenses significantly enhance the mortality caused by opportunistic gut microbes in insects.
• The combined assault of plant defenses and microbial infection overwhelms insect hosts, leading to increased mortality.
• This interaction highlights a critical ecological dynamic influencing insect population dynamics.