Parasitism by Phorids on Leaf Cutter Ants Atta sexdens (Linnaeus, 1758) (Hymenoptera: Formicidae) in Natural and Agricultural Environments.

The leaf cutter ant Atta sexdens (L.) (Hymenoptera:Formicidae) causes huge economic losses to agriculture in the Neotropics. In natural environments, parasitic flies of the Phoridae family are natural enemies of leaf cutter ants. Habitat modification is considered one of the main causes of species decline. In this study, we compare the occurrence of parasitic phorids on A. sexdens and the parasitism that they cause on colonies located in agricultural and natural habitats. Phorid flies were collected from trails, nest entrances, and cutting sites when they were hovering over workers of A. sexdens nests from natural vegetation, farmland, and Eucalyptus plantation areas. Simultaneously, workers from A. sexdens nests were collected from these environments, and the parasitism rates of phorids were determined. Ants were parasitized by Apocephalus attophilus, A. vicosae, Eibesfeldtphora bragancai, E. tonhascai, and Myrmosicarius grandicornis. The highest parasitism rate (3.54 ± 0.49%) was registered for nests from the Eucalyptus plantations. The rate of parasitism of nest from natural vegetation was 2.42 ± 0.40% and in the farmland was 1.91 ± 0.39%. The parasitism of each phorid genus varied according to habitat and month. Apocephalus attophilus had the highest parasitism in the three habitats and displayed biological characteristics that give it great potential as a biological control agent for A. sexdens. Eibesfeldtphora spp. had higher parasitism in a natural environment and M. grandicornis in agricultural environments. Apocephalus attophilus and M. grandicornis seemed able to occur in a wide variety of habitats that their hosts occupy, but the rate of parasitism by Eibesfeldtphora spp. was significantly lower in agricultural environments.

Reproductive ecology of phorid parasitoids in relation to the head size of leaf-cutting ants Atta sexdens Forel.

The leaf-cutting ant Atta sexdens Forel (Hymenoptera: Formicidae) is one of the most damaging agricultural pests in the Neotropics. Management strategies predominantly rely on the use of general insecticides. What is needed are more species-specific and environmentally friendly options. Parasitioids such as phorid flies (Diptera: Phoridae) may be one such option, but a greater understanding of the ecology of the flies and their ant hosts is essential to devise biological control strategies. Here we report parasitism rates, ant host size, parasitoid abundance per host and resultant sex ratios of two phorid species Apocephalus attophilus Borgmeier and Eibesfeldtphora tonhascai Brown parasitizing A.sexdens. The two species achieved parasitism rates of 1.48 and 1.46%, respectively and the pupal period was 14.7 ± 1.1 days and 22.1 ± 2.8 days, respectively. There was no significant difference between the head capsule width of ants parasitized by either A. attophilus or E. tonhascai. Likewise, there was no significant effect between the head capsule width of parasitized and unparasitized ants for both species. A significant positive correlation was found between the head capsule width of the parasitized ants and the number of adult parasitoids A. attophilus emerged. Ants parasitized by E. tonhascai survived significantly longer than those parasitized by A. attophilus. There was no significant effect of ant head width on the sex ratio of the offspring of either parasitoid species and no significant difference in the sex ratio (male: female) of their offspring. In summary, these data addressed here are important steps when considering natural enemies for biological control. Studying survival of the parasitized ants, parasitoid offspring sex ratio and host size preference allows for a better understanding of ant natural biological control in the field and can help in rearing of A. attophilus and E. tonhascai in laboratory.