Haemolymph Defense Capacity of the Neotropical sawfly Aneugmenus merida against Ant Predation

Abstract

The defensive characteristics of the sawflies have received special attention due to the involvement of toxic compounds obtained from host plants. In this context, the haemolymph-based defense is one of the strategies known in sawflies to dissuade the attack of predators. Aneugmenus merida is a neotropical sawfly whose larvae are herbivorous on the toxic bracken fern Pteridium spp. The present study examines the defensive properties of the A. merida larval haemolymph and its possible link with the chemistry of its host plant. We report the behavior of the solitary hunter ant Odontomachus chelifer towards A. merida larvae under laboratory conditions. In addition, we studied the liquid intake behavior of the ants provided with solutions of crude haemolymph, bracken extracts, and its fractions. A. merida larvae showed a marked defensive capacity against the ants. The inhibition of the attack was observed during the stages of antennal contact and mandibular blow, suggesting that larval defensive capacity is due to factors present in the integument and haemolymph. Aqueous and methanolic fractions of haemolymph and bracken also deterred feeding. Although some common compounds were detected in the haemolymph and bracken fractions, they were in very small quantities, suggesting that they are not responsible for the bioactivity. Therefore, the hypothetical connection between the host plant chemistry and larval defensive capacity could not be evidenced. We suggest that the deterrent compounds present in the haemolymph and integument could be jointly acting in the sawfly’s defensive strategy.