Ant-Lion (Neuroptera: Myrmeleontidae) associated with nests of Dorymyrmex thoracicus (Hymenoptera: Formicidae): testing the optimal foraging theory


The Optimal Foraging Theory postulates a set of actions in which the organisms maximize food uptake per unit of time, even including the choice of nesting site and shelter.To optimize the capture of prey, the shelter of the predator should be in areas that offer favorable abiotic conditions, high number of prey and low number of others predators/competitors. The larvae of ant-lion (Neuroptera: Myrmeleontidae) use sit-and-waiting strategy of foraging, building funnel-shaped traps on the sand while remaining on the bottom to catch small organisms.In this study, our aim was to test if ant-lion build their nests near to the vegetation due the higher abundance of prey associated with the shaded microhabitat. We expect that frequency and density of ant-lion funnels will be higher in areas close to vegetation, as well that areas with the higher funnel density should have funnels with smaller diameters. The study was conducted in an area of Caatinga from the Catimbau National Park, Pernambuco, Brazil. In this studied area the nests of the ant D. thoracicus (Hymenoptera: Formicidae) are abundant and have a high amount of ant-lion nests near them. We sampled 10 nests of D. thoracicus near shrub (treatment) and 10 nests in distant areas of vegetation (control). Around each nest was delimited a plot of 16 m2 where we countthe funnels and measure their diameters. We use a Chi-square test to check the frequency of funnels and t-test for their density, near and far from the vegetation and a linear regression to verify the relationship between density and diameter of the funnels. We found a higher frequency of Myrmeleontidae funnels in nests of D. thoracicus located near the vegetation (55), than innests far from the vegetation (3) (χ2 = 93.24, DF = 3, p<0.01). The funnels density in nests near vegetation was higher compared to the nests far from to vegetation (t = 3.55; df = 18, p <0.01). However, the funnels density did not influenced their diameter (R2 = 0.07, df = 1; p = 0.60). Our results indicate that the vegetation provides suitable microhabitat for ant-lion larvae, probably because the temperature is mild and in these sites the transit of small invertebrates, including ants, must be higher compared to areas without vegetation. However, the higher density funnels did not influenced their size. This may be occurring due to the high availability of resources in the environment, reducing the individual’s competition. The ant- lion larvae seem to be foraging in areas with more preys which can reduce the cost-effectiveness of foraging.(MCTI/CNPq/FAPs n 342012 – PELD).

In XXII Simpósio de Mirmecologia: an international ant meeting