Evidence refuting the interference competition hypothesis for native lady beetle decline

The decline of native coccinellid populations coincides with the establishment of exotic coccinellids. This led to the proposal of interference competition via intraguild predation (IGP) of native species by exotic coccinellids as a hypothesis to explain the decline. This hypothesis has been supported in laboratory experiments which have shown that exotic coccinellids can be a significant predator of native coccinellid egg masses. We expanded upon these studies by measuring the intensity of egg predation experienced by a declining native (Hippodamia convergens) common native (Coleomegilla maculata) and common exotic (Harmonia axyridis) coccinellid within the field. Egg predation experiments in three habitats (soybean, alfalfa, and grassland) within eight Ohio counties illustrated that native coccinellid eggs incurred significantly more predation than exotic coccinellid eggs. These findings provided additional evidence in support of the interference competition hypothesis. Though, an assumption of the predation experiments was that exotic coccinellids were attacking the egg masses. Our next step was to test this assumption by directly observing the predators that attacked egg masses in the field. We placed surveillance cameras in our three focal habitats and focused them on egg masses of either H. convergens or H. axyridis. We found that exotic coccinellids are not significant predators of native coccinellid egg masses in soybean, alfalfa and grassland fields. Instead, Opiliones , Acrididae, Plulmonata, and Tettigoniidae were the major egg predators found within our field sites. These data refute interference competition via egg predation by exotic coccinellids as a mechanism to explain the decline of native coccinellids.