Compatibility of endophytic fungal entomopathogens with plant extracts for the management of sweetpotato whitefly Bemesia tabaci Gennadius (Homoptera: Aleyrodidae)

Abstract

The effects of individual and combined application of endophytic fungal entomopathogens (Beauveria bassiana strain NATURALIS and Metarhizium brunneum strain BIPESCO5) and aqueous extracts of two medicinal plants (Calotropis procera and Inula viscosa) on the survival and development of the sweetpotato whitefly (Bemisia tabaci) were investigated for the first time. Brassica oleracea was inoculated through foliar spray of plants with the conidial suspension of fungal strains, and the endophytic colonization of different plant parts (leaf, stem, and root) was confirmed 7 days post-inoculation (7 dpi); when B. tabaci adults were introduced into plants and prior to plant extract application. 48 h later, whitefly adults were removed and the egg bearing leaves of respective treatments were sprayed with aqueous plant extracts. Although all treatments had a significant negative effect on the survival of different B. tabaci developmental stages compared to control, an increase in percentage mortality among all developmental stages was consistently observed when combined applications of endophytic entomopathogenic fungi and aqueous plant extracts were used; irrespective of fungal strain or plant extract. However, the increase was not always additive. Combined application of endophytic entomopathogenic fungi and plant extracts had an additive effect on mortality of nearly all whitefly developmental stages when endophytic B. bassiana was applied with C. procera extract. On the other hand, when endophytic M. brunneum was applied with either plant extract, the combined effects were always significantly higher than effects achieved by individual treatments; but occasionally additive. Similarly, whitefly development was significantly delayed when individual and combined applications of endophytic fungal entomopathogens and plant extracts were used; but the delay was most significant in response to combined applications. Our results provide the first report for the compatible use of fungal entomopathogens, applied as endophytes, with aqueous plant extracts for the management of insect pests; particularly B. tabaci.