Detecting predation and scavenging by DNA gut-content analysis: a case study using a soil insect predator-prey system

Area of Science:

• Ecology
• Entomology
• Molecular Biology

Background:

• White grubs are significant agricultural pests damaging crops by feeding on roots.
• Understanding the natural enemies controlling white grub populations is crucial for sustainable agriculture.
• Investigating soil food web interactions is challenging with traditional methods.

Purpose of the Study:

• To develop and validate a polymerase chain reaction (PCR)-based method for identifying prey in soil insect predators.
• To determine if PCR can detect both fresh and decaying (carrion) white grub prey.
• To assess the efficiency of PCR in identifying prey consumed by predators.

Main Methods:

• Larvae of Poecilus versicolor were fed fresh Melolontha melolontha larvae or 1- to 9-day-old carcasses.
• DNA from predator gut contents was analyzed using PCR to amplify mitochondrial cytochrome oxidase subunit I fragments.
• The detectability of prey DNA was assessed at different time points and with varying DNA fragment lengths.

Main Results:

• PCR successfully detected white grub DNA in predators fed both fresh and carrion prey.
• Prey DNA was detectable up to 32 hours after feeding, with detectability decreasing for longer DNA fragments.
• Carrion prey was detected by PCR as efficiently as fresh prey, regardless of cadaver age.

Conclusions:

• PCR-based techniques are highly efficient and sensitive for detecting both fresh and carrion prey in insect predators.
• This method provides a valuable tool for studying predator-prey dynamics in soil ecosystems.
• Distinguishing between active predation and scavenging requires complementary approaches alongside sensitive DNA detection methods.