Opposite effects of different mineral oil treatments on Macrosiphum euphorbiae survival and fecundity

Mineral oil has been considered for several decades as an effective mean to control aphids and reduce the spread of non-persistent viruses. Mineral oil seems to reduce virus transmission efficiency interfering with the binding of the virions in the aphid stylets. However, several studies have shown the possible disruption of host selection process by mineral oil and some works have demonstrated a direct effect on the aphid vector. In this study the insecticidal properties of mineral oil (Finavestan EMA) alone against Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae) were evaluated through the three main routes of exposure (topical contact, inhalation and ingestion). Results showed that no aphid survived after topical contact at oil concentrations ranging from 3 to 100% v/v. However, surprisingly, at a lower concentration (0.3%), survival was not affected but fecundity was enhanced. Moreover, exposure to oil volatiles enhanced aphid survival at the highest concentrations (30 and 100%) and daily fecundity at the lowest ones (0.3 and 3%). Delivered via artificial diet, mineral oil only affected aphid survival at the 0.3% concentration. This study demonstrates that mineral oil alone, regardless of a potential plant effect can induce either probiotic effects or toxic effects, depending on the mode of application and the concentration tested. These results can be of significance for the understanding of mineral oil properties in the fields.