Assessing the effect of soil treatments with the entomopathogenic fungus Metarhizium anisopliae (Metchnikoff) Sorokin against puparia of Bactrocera oleae (Diptera: Tephritidae) on soil dwelling non target arthropods

Abstract

The objective of this study was to determine the persistence of the autochthonous Metarhizium anisopliae EAMa 01/58-Su isolate in the soil when applied beneath olive trees for controlling olive fly puparia and to elucidate its possible effect on non-target soil dwelling arthropod communities. For that, we selected 200 olives trees in an organic olive orchard at the province of Málaga(Spain) to be sprayed either with a 2.5 x·107 conidia m-2 suspension of the fungus on the ground beneath the tree canopy (100 trees) or with the blank formulation as controls (100 trees). Before fungal treatments, we selected 10 trees from the treated ones for evaluating both the possible presence of indigenous entomopathogenic fungi in the soil by using the Galleria Bait Method and the evolution of the conidial densities in the soil after spraying. The entomopathogenic fungus Beauveria bassiana (Balsamo) Vuill. was the most common species, being found in all the samples, while M. anisopliae was found only in one sample. After spraying the 100 treated and 100 control trees, soil samples beneath the 10 selected trees from the top 10 cm were taken to calculate the number of conidial forming units per gram of soil at 1, 7, 14, 28, 35, 42, 49, 56 and 63 days after treatment respectively. Our preliminary data indicate that the soil ecosystem favours the persistence of this autochthonous isolate, which could allow long term protection of the crop against olive fly puparia. In order to assess the possible effect of the fungal treatment on soil arthropod populations, 40 pitfall traps (7.5 cm diameter by 10 cm deep) placed beneath the tree canopy of randomly selected 20 treated and 20 controls trees, were sampled every two weeks. Our preliminary data indicate that formicidae species are the most abundant arthropods trapped, but no infected insects have been found in field as a result of the treatment to now.