Botanical extracts from Dodonaea viscosa (Sapindales: Sapindaceae) reduce hemocyte counts from Spodoptera exigua (Lepidoptera: Noctuidae) with potential insecticidal synergism with Isaria fumosorosea (Hypocreales: Cordycipitaceae)

Abstract

ABSTRACT Some botanical extracts affect the cellular immune system of insects by interfering with normal hemocyte function. This gives rise to diminution in cellular immunity and causes a decrease in insect defense. This investigation evaluated the effect of acetonic (AcEDv) and methanolic (MeEDv) extracts of Dodonaea viscosa (1000, 2000, and 4000 ppm) on the total hemocyte count (THC) present in the hemolymph of Spodoptera exigua, as well as on its insecticidal activity, on its own and in combination with the entomopathogenic fungus Isaria fumosorosea. Water and Tween® were used as negative controls and Lorsban® as a positive control. Second instar S. exigua larvae were separately fed an artificial diet incorporating both extracts. THC was significantly lower in AcEDv treatment at 1000 ppm and MeEDv treatment at 1000 and 4000 ppm compared with negative controls. The insecticidal action of the individual extracts and those in combination with the conidia of I. fumosorosea manifested from day 21, while at day 28, the AcEDv at 1000 and 2000 ppm and the MeEDv at 4000 ppm applied with the fungus revealed mortality percentages higher than 50% and a significantly higher mortality compared with the negative controls. In conclusion, the extracts of D. viscosa reduced the total THC of S. exigua and suggest that the application of this plant extract presents a synergistic effect on the mortality of S. exigua exposed to entomopathogenic fungus I. fumosorosea.