Abstract
Atta bisphaerica (Forel) is a leaf-cutting ant that specializes on grass and causes productivity losses in sugar cane fields and pastures. Three phorid species, Apocephalus attophilus (Borgmeier), Myrmosicarius grandicornis (Borgmeier) and Eibesfeldtphora bragancai (Brown), have been found parasitizing A. bisphaerica workers. These parasitoids can reduce plant material transported into the nests and ant traffic on the trails. Therefore, phorid flies have been considered potential biological control agents for leaf-cutting ants. Here, we evaluated which parasitoid species attack the leaf-cutting ant A. bisphaerica in pasture areas of a Brazilian Savannah-Atlantic Forest ecotone, parasitism rate, effect of host size, sexual dimorphism and sex ratio of the emerged parasitoids. Four nests of A. bisphaerica were selected in pasture areas from August 2016 to August 2017, with 400 workers collected from each colony monthly. A total of 23,714 A. bisphaerica workers were collected during the study, of which 236 (0.99%) were parasitized by phorid parasitoids. Apocephalus attophilus, E. bragancai and M. grandicornis parasitized 217, 17 and 2 ants, respectively. The higher parasitism rate was found in the hottest/rainy season of the year. Non-parasitized ants survived longer than those parasitized by A. attophilus. The larval and pupal periods of this parasitoid were 2.2 ± 0.8 and 16 ± 1.4 days, respectively, and the number of pupae per parasitized ant ranged from 1 to 7. The number of A. attophilus pupae per host increased with the host head size. Likewise, the size of the adult parasitoids also increased according to the host ant. Apocephalus attophilus females were larger than males and the sex ratio (male: female) did not differ from 1: 1. Our results showed that A. attophilus would be a potential biocontrol agent of leaf-cutting ants because it produces multiple larvae per host, allowing a great production of parasitoids with short developmental time and kills the host ant faster than other phorids.
Highlights
Leaf-cutting ants of the genus Atta and Acromyrmex (Hymenoptera: Attini) are recognized as important agricultural and forest pests, cutting fresh plant material from a wide range of plant species for cultivation of the symbiont fungi, which feed the entire colony [1,2]
A total of 23,714 A. bisphaerica workers were collected during the study, of which 236 (0.99%) were found to be parasitized by phorid parasitoids
The parasitism rate of A. bisphaerica workers by phorids observed in this study (0.99%) was below 6%, similar to that reported for A. bisphaerica (4.37%) [18], A. laevigata (2.8 and 5.36%) [36,37], A. sexdens (1.57 and 2.94%) [37,31], Atta vollenweideri (Forel) (0.08 to 3.88%) [8] and Solenopsis spp. (0.2 to 2.4%) [35,38] by their respective phorid parasitoids
Summary
Leaf-cutting ants of the genus Atta and Acromyrmex (Hymenoptera: Attini) are recognized as important agricultural and forest pests, cutting fresh plant material from a wide range of plant species for cultivation of the symbiont fungi, which feed the entire colony [1,2]. Atta bisphaerica (Forel) is a grass-cutting specialist that causes losses in sugar cane and managed pastures [3,4]. Use of biological agents for pest suppression is a promising area, but development of biological control programs requires knowledge of the biology and behavior of natural enemies [8,9]. [13,14,15] reinforces the possibility of using these natural enemies to manage leaf-cutting ants. The presence of phorids changes ant behavior, reduces ant traffic on trails and the amount and weight of plant material transported [11,12,16]
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