COS 86-2
The effects of consuming toxic monarch caterpillars on Chinese mantid fecundity
Monarch caterpillars feed on milkweed host plants and sequester toxic cardenolides as a chemical defense against predation. Although this strategy is effective against most predators, the Chinese mantid guts monarch caterpillars and consumes the remaining biomass without any apparent ill-effects. We have found that while both body and gut material contain similar overall cardenolide concentrations, different specific cardenolides are present in each tissue. Though mantids suffer no apparent ill-effects from consuming monarch bodies, they are still ingesting toxins that may have long-term impacts. We tested whether consuming monarch caterpillars reduces mantid fecundity. We assigned lab-reared adult mantids into one of four toxicity groups (non-toxic control, low, medium, and high) that differed in the number of caterpillars consumed over a 15-day period following eclosion. After this time, mantids were fed crickets daily until they were sacrificed and dissected on day 35. We determined the number of eggs produced, average egg length, and total egg weight.
Results/Conclusions
Monarch consumption did not affect mantid egg production. Contrary to expectation, mantids in the high-toxicity treatment had longer eggs and devoted a greater percentage of their body mass to egg production than did mantids in the control treatment. Mantids in the control treatment were smaller than those in the high-toxicity treatment but there were no between-treatment differences in total prey biomass consumed over the 35-day experiment. Thus, consuming monarch caterpillars did not reduce mantid fecundity. Together with previous research, our results indicate that Chinese mantids suffer neither acute nor chronic ill-effects from consuming cardenolide-laden monarch caterpillars.