Manipulation of fire ant density, Solenopsis spp., for short-term reduction of Diatraea saccharalis larval densities in Brazil

The sugarcane borer, Diatraea saccharalis (Fabr.) is the main sugarcane pest in Brazil. In the State of São Paulo, the main active population control of D. saccharalis is by inundative releases of the exotic parasitoid, Cotesia flavipes (Cam.). However, the production of C. flavipes in sugar mills entails costs and few studies have evaluated the effects of native predators on sugarcane borer populations. Using a simple colony translocation method, we evaluated the effect of fire ants (Solenopsis spp.) on population densities of D. saccharalis and concurrently upon rates of parasitism by classical biological control agents in the São João sugar mill in the State of São Paulo, Brazil. The translocation technique proved to be feasible and economically possible. Sugarcane borers were sampled in each of the 5 areas for each treatment in two 1.4 x 5.0 m (7 m²) points (sample size), by opening and visually examining all canes. The average numbers and its respective standard deviations (SD) for D. saccharalis population densities before and after colony translocations considering 0, 5, 10 and 15 colonies added per 0.5 ha were, 9.2 ± 5.9, 8.4 ± 3.4, 9.0 ± 6.9, 9.4 ± 8.1 and 3.2 ± 1.8, 2.8 ± 2.7, 2.6 ± 1.5, 3.8 ± 2.8, respectively. However, we detected no significant changes in sugarcane borer densities with respect to ant colony densities over a two-week period, none of which were greater than for no colony additions. No effects of colony translocations on parasitism rates of braconid and tachinid parasitoids on D. saccharalis were detected. Thus, although the translocation technique was economically feasible, no reductions of D. saccharalis densities were produced by colony additions, and may not be a viable alternative for D. saccharalis population reduction, especially at the low population levels which prevail in Brazil