Análise de predação intraguilda em alfafa

Abstract

Aphids are considered as pests in several crops causing direct and indirect damage to the plants. In alfalfa fields (Medicago sativa), the species Acyrthosiphon pisum, Acyrthosiphon kondoi, Aphis craccivora and Therioaphis trifolii are found very often. Their natural enemies include predators and parasitoids among others. The aim of this work was to analyze the seasonal fluctuation of aphid populations and its relationship with climatic variables through correlation tests; in laboratory, to select the aphid species which were abundant in the field, having parasitoids and coccinelids predators associated with the intention of using them in serologic tests aiming to observe a possible intraguild predation. The serological technique is based on reactions as antigen/antibody where the antibodies are obtained to the specie of interest. The gathering of aphids, predators and parasitoids occurred from March 2013 to May 2014 in experimental alfalfa crioula fields located at Embrapa Pecuária Sudeste Unit, São Carlos, SP. Therioaphis trifolii was the most abundant aphid during the sampling period, followed by Acyrthosiphon pisum. Considering all species the populational peak occurred in September 2013 and the lower in January 2014. According to the tests, all species had no correlation with the rain, and no other variable presented significant influence in aphid’s seasonal fluctuation. 1208 coccinelids (Coleoptera: Coccinellidae) of six species were sampled and the three with more specimens, Harmonia axyridis, Hippodamia convergens and Cycloneda sanguinea respectively, were separated to be part of the serological tests. A typical pattern predator-prey was observed. No species of parasitoids were found in T. trifolii and one species of parasitoid, Aphidius ervi (Hymenoptera: Aphidiidae) was found on A. pisum, and this led to its choice to the intraguild predation tests. According to the serological tests results, 52 among 485 coccinelids tested had traces of the parasitoid in its gut contents, that means 10,72% of the coccinelids ate parasited aphids. Feeding tests have shown that the parasitoid A. ervi can be detected up to 72 hours after its ingestion.