Intraguild predation (IGP) occurs when two predators competing for the same resource consume one another. Theory predicts that low quality resources drive communities to exclusion of both predators, while high quality resources may exclude the bottom predator. IGP also influences the dynamics between predators and pathogens. A large number of IGP communities occur where predators and pathogens compete for a shared resource. In these systems, predators may be affected by low quality prey and may also change the dynamics of infection within the prey population.
Specifically, we used lab and field studies to investigate three questions. 1) What influence do infected soybean loopers (prey) have on the fitness of spined soldier bugs (predators) compared to healthy soybean loopers? 2) Do soldier bugs prefer healthy or infected prey? 3) How do soldier bugs change the way a virus spreads through a caterpillar population. We predicted that infected prey would negatively influence predator fitness, predators would not exhibit preference, and that soldier bugs would reduce the proportion of infected caterpillars during an infection.
Results/Conclusions
Survival was not different between soldier bugs that fed on healthy caterpillars compared to soldier bugs that fed on infected caterpillars (p = 0.79). We expect that fecundity and longevity will both be lower in soldier bugs reared on infected caterpillars compared to healthy caterpillars.
Our choice test results showed that predators did not exhibit preference for healthy or infected caterpillars over all time periods after infection (p = 0.36). We tested 20 soldier bugs per time period, with time periods being consecutive 24 hour intervals after infection. However, once caterpillars dried from virus leaking out (post-mortem), predators avoided the cadavers (p < 0.001). Infected prey represent a low quality resource for the predators and the lack of preference negatively influences fitness. This is in line with current literature on intraguild predation between predators and pathogens for a shared resource.
Finally, preliminary results suggest that treatments with predators will have the highest transmission rates. Treatments with healthy predators had 11% infection in healthy caterpillars and treatments with predators without mouth parts had 10% infection rate. The treatment without predators had 8% infection rate. The differences between groups was not significant. Control groups without virus had no infection.