The effect of Senna mexicana chapmanii density on herbivore biocontrol by parasitoids

Senna mexicana chapmanii, an ornamental and Threatened species native to Florida, is often attacked by folivores of Sulphurs in the order Lepidoptera. Important natural enemies of Sulphur butterflies are parasitoids of the order Diptera and Hymenoptera. Here I describe an observational study, investigating the effects of plant density on folivore density and parasitism in Senna mexicana chapmanii.

 Senna mexicana chapmanii plantations, in an agricultural and urban area located nearby Protected Areas in Florida, were set up at different densities. The density of S. mexicana plants varied between low, medium and high. At the beginning of June 2015 mean larval densities (larvae/plant) and parasitism (percentage of larvae attacked by parasitoids) were recorded in each plantation. Mean larval densities varied between --- and --- larvae per plant and were --- correlated to plant density. Parasitism varied between --- and ---%, and was ---- significantly related to plant or larval density.

The data suggest that parasitoid can function as an important biocontrol agent against Sulphur folivors, but parasitism varies widely between areas. The reason for the --- folivore densities in dense plantations is currently ; elucidating the mechanism behind this pattern will be important in order to understand the factors that regulate the density of Sulphurs in the field.