Impact of soil texture on conidia movement and residual effect of entomopathogenic fungi applied through irrigation to control fruit-fly pupae in mango orchards

Abstract

While most measures to control Ceratitis capitata (Wiedemann) target larvae and adult insects, entomopathogenic fungi (EPF) have shown promising results against pupae in the soil. This work aimed to evaluate the effect of soil texture on conidial transportation, residual effect, and C. capitata mortality caused by two virulent strains of EPF. The strains were applied to soil columns previously packed with a sandy or a clayey Ultisol using simulated drip irrigation. There were no statistical differences in conidial transportation through soil layers between the sandy and the clayey Ultisol. >90% of conidia were retained in first 40 mm. However, Beauveria bassiana BbLCB289 applied in the sandy soil showed higher pupae and adult mortality. Premixing EPF conidia with siloxane 0.05% v/v increased the percolation of conidial suspensions of BbLCB289 in the sandy soil, but no effect was observed on Metarhizium anisopliae MaLCB255. However, it did not interfere with insect mortality but showed an increase in post-emergence mortality in insects from columns treated with MaLCB255. Seemingly, conidial morphology of the Metarhizium strain interacted with soil pore reducing its percolation rate. Overall, the results showed that the residual effect was only slightly affected by strain and soil texture, and ranged between 27 and 34 days. Finally, field application of experimental and commercial EPF strains in a sandy Ultisol resulted in insect mortality between 52 and 68%