Susceptibility of Rhagoletis suavis (Diptera: Tephritidae) maggots to entomopathogenic fungi

Authors: NISAR, MUHAMMAD - University Of Agriculture - Pakistan; Behle, Robert; Dunlap, Christopher; Goett, Erica; IQBAL, MUBASHAR - University Of Agriculture - Pakistan; GOGI, MUHAMMAD - University Of Agriculture - Pakistan

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2019
Publication Date: 7/1/2019
Citation: Nisar, M.J., Behle, R.W., Dunlap, C.A., Goett, E.J., Iqbal, M., Gogi, M.D. 2019. Susceptibility of Rhagoletis suavis (Diptera: Tephritidae) maggots to entomopathogenic fungi. Southwestern Entomologist. 44(2):431-436. https://doi.org/10.3958/059.044.0208.
DOI: https://doi.org/10.3958/059.044.0208

Interpretive Summary: Fruit flies in the Rhagoletis genus include the apple maggot, western cherry fruit fly, and walnut husk fly. These flies damage many high value fruit and nut commodities when maggots feed directly on ripening fruit. These insects are often controlled by chemical insecticide sprays to kill the adult flies before they lay eggs directly in the fruit. Using the walnut husk maggot, we found that larvae emerging from the husks to pupate in the soil were susceptible to infection by several common fungal diseases that are specific to insects. Finding that the fungus known as Metarhizium was most infective of the pathogens tested, when combined with knowledge of ARS proprietary fungal fermentation production techniques, supports further development of Metarhizium as a biopesticide for application to the soil to break the insect's annual life cycle as part of an integrated pest management system that reduces the need for pesticide applications when fruit is ripening in the field.

Technical Abstract: Most tactics for control of walnut husk-maggot, Rhagoletis suavis, target adult flies before eggs are laid to prevent damage by maggots feeding in commercial walnuts. An alternative strategy is to control maggots as they exit the fruit to pupae in the soil to reduce the subsequent year’s adult density prior to egg laying. The present study was carried out to evaluate the insecticidal activity of three entomopathogenic fungi, Beauveria bassiana GHA, Metarhizium brunneum F52 and Isaria javanica strain 439 against R. suavis maggots collected from black walnut husks. The Rhagoletis species was confirmed by mitochondrial cytochrome c oxidase subunit I gene sequencing, which indicated that the collected insects were R. suavis with 99% homogeny to reference data. Insect cadavers and subsequent mycosis expressed typical physical characteristics of B. bassiana (pink cadavers and white sporulation), M. brunneum (olive green sporulation) and I. javanica (rapid white mycelia with slightly pink sporulation). Each of the fungal treatments caused higher mortalities of maggots with exposure to higher concentrations of fungal conidia. Probit analysis showed that M. brunneum proved 149× and 145× more potent than the B. bassiana and I. javanica against exposed maggots, respectively. This discovery that the Metarhizium fungus has a high level of insecticidal activity against these maggots supports further development of this fungus as a biological control agent not only for Rhagoletis flies but also for other soil-inhabiting pests. Further, a soil application of this entomopathogenic fungus will likely fit as a control application suitable for organic production of walnuts.