Factors altering the temporal and within-plant distribution of coccinellids in corn and their impact on potential intra-guild predation

In New York, the primary coccinellid in corn and sweet corn (Zea mays, L.) has historically been Coleomegilla maculata (DeGeer). However, Harmonia axyridis (Pallas) has also been observed the last few years. The objectives of this study were to document the level of establishment of both species in corn and sweet corn and to understand their interactions. The temporal and within-plant distributions of all coccinellids were recorded for 3 yr. The results indicated that H. axyridis and C. maculata were the only abundant coccinellids in corn and sweet corn, with adults and larvae of both species having distinct temporal and within-plant distributions. C. maculata adults were found earlier in the season and lower on the plant than H. axyridis adults. Larvae of both species were often found at the same time and were lower on the plant than their respective adults. Temporal distributions of both species were correlated to crop maturity, aphid density, planting date, and corn type, but not to nearby vegetation. The within-plant locations were correlated to crop maturity, aphid density, planting date, nearby vegetation, and the presence of conspecific coccinellids. While the distribution of each population was unique, some C. maculata and H. axyridis shared time and space, providing the potential for intra-guild predation. An encounter between H. axyridis and C. maculata was most likely to occur when the corn bad high aphid populations during pollen shed. These extra-guild food sources minimize intra-guild predation, allowing these two species to co-exist in New York corn and sweet corn fields.