A new aphid IPM strategy based on the use of endophytic entomopathogenic ascomycetes that reduces treatment risks to the generalist predator Chrysoperla carnea (Stephens)

Abstract

The melon aphid Aphis gossypii is one of the most damaging and economically important crop pests. Entomopathogenic ascomycete (EA) have shown great potential in managing this pest, with several mycoinsecticides available on the market. Recent studies also highlight the systemic efficacy of EA endophytic strains, targeting aphids through the plant and impacting their survival and reproduction. EA endophytic application prevents direct contact between EA and beneficial insects which increases their safety. Indeed, EA endophyte compatibility with other biological control agents, such as entomophagous predators, has been demonstrated under laboratory conditions. However, these results need to be validated using different application methods and under greenhouse conditions. In this study, we evaluated the biocontrol potential of two endophytic EA strains against A. gossypii in melon crops under greenhouse conditions. Based on their known endophytic behavior, Metarhizium brunneum strain EAMa 01/58-Su was applied as a foliar spray while Beauveria bassiana strain EABb 01/33-Su was applied as a seed dressing. Furthermore, the compatibility of these EA applications with the predator Chrysoperla carnea was assessed. Two repetitions were made in a greenhouse in Córdoba (Spain), the first in summer and the second in autumn. It is noteworthy that, in summer, foliar spraying with M. brunneum resulted in 35.0% aphid mortality and a 20.4% reduction in total per capita nymph production (TCNP) on sprayed leaves. In contrast, leaves not sprayed with the fungal suspension but endophytically colonized caused 70.0% aphid mortality and a 12.6% reduction in TCNP, which demonstrates the systemic potential of this fungus. Compatibility between C. carnea and M. brunneum was also demonstrated; there was a significant increase in prey consumption on endophytically-colonized leaves compared with predation levels observed in control plants. Seed dressing with B. bassiana led to 55.0% aphid mortality and a 19.2% reduction in TCNP but had no significant effect on C. carnea predation. The same trends were observed in autumn, although colder temperatures reduced aphid mortality. Our results highlight the potential of fungus-predator biocontrol strategies within an aphid Integrated Pest Management program under greenhouse conditions.