Susceptibility of the developmental stages L2 and L3 of Phyllophaga elenans to a native strain of Heterorhabditis sp. at greenhouse

Abstract

The effect of 6 native entomopathogenic nematodes (EPN) strains over the 2^nd instar of Phyllophaga elenans was evaluated. The nematode strain with the best results, Heterorhabditis sp. CIA-NE 07, was evaluated at 125, 225, 375, 500 y 625 nematodes.larva^-1 to determine its pathogenicity over the 2^nd and 3^rd instar larvae of P. elenans. At the 7^th day after inoculation, all doses except 125 nematodes.larvae^-1 caused a significantly mortality of the 2^nd instar, in comparison to the control, in which no deaths occurred. At the 14^th, 21^st, and 28^th day all the inoculated treatments were significantly different from the control; the highest dosis caused 68% of mortality at day 30. It was  determined that the median lethal doses corresponded to 475 nematode.larvae^-1 and the median lethal time was 7.5, 8.5 y 17.5 days for the 625, 500 and 225 nematodes.larvae^-1 concentrations, respectively. On day 7, EPN inoculation on third instar did not present significant differences among treatments; while at days 14, 21 and 28 only the 500 and 625 nematodes.larvae^-1 doses presented a significantly mortality than the control. The highest mortality (24%), was obtained at day 30 with the 625 nematode.larvae^-1 dose. The observed differences between second and third instars could be due to defense or escape mechanisms present in the 3^rd instar of P. elenans.