Uniformity of petroleum-derived spray oils: lethal and sublethal effects on a herbivore pest and its parasitoid

Abstract

1 Petroleum-derived spray oils (PDSO) are widely used and recommended in many integrate pest management programmes and in organic agriculture against several pests. However, there are numerous discrepancies in their efficacy against pests and, more interestingly, in their side effects on natural enemies. 2 In the present study, we used the citrus key pest Aonidiella aurantii Maskell (Hemiptera: Diaspididae) and its main parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinedae) as models to evaluate both the lethal and sublethal effects of four commercial PDSO on different instars of the herbivore, as well as on the adult and immature stages of the parasitoid. 3 The four PDSOs displayed similarly high mortalities against young instars of A. aurantii. However, most adult females survived all PDSO applications, and the fecundity of the surviving females was not altered. 4 PDSOs were harmless to the parasitoid A. melinus because the survival (acute toxicity), longevity and fecundity of the surviving adults (sublethal effects) were not affected. Similarly, immature emergence was not affected by any of the four PDSOs after spraying the parasitized hosts. 5 Overall, the results of the present study confirm the environmental-friendly profile of PDSOs against natural enemies and demonstrate a similar performance for PDSOs when they were correctly sprayed under the same conditions.