Inoculative Releases and Natural Spread of the Fungal Pathogen Entomophaga maimaiga (Entomophthorales: Entomophthoraceae) into U.S. Populations of Gypsy Moth, Lymantria dispar (Lepidoptera: Erebidae)

Abstract

While emphasis with entomopathogens has often been on inundative releases, we describe here historic widespread inoculative releases of a fungal entomopathogen. Several U.S. states and municipalities conducted inoculative releases of the gypsy moth, Lymantria dispar (L.) (Lepidoptera: Erebidae), pathogen Entomophaga maimaiga Humber, Shimazu et Soper (Entomophthorales: Entomophthoraceae) after 1993, as gypsy moth populations spread into the Midwest and North Carolina. This Japanese pathogen first caused epizootics in northeastern North America in 1989 and methods for its inoculative release were tested and proven to be effective from 1991 to 1993. After 1993, spores in soil or in late instar cadavers were collected during or after epizootics and were released inoculatively into newly established populations of this spreading invasive; the goal was that spores would overwinter and germinate the next spring to infect larvae, thus speeding pathogen spread and hastening the development of epizootics in newly established populations. The fungus was released in gypsy moth populations that were separated from areas where the fungus was already established. In particular, extensive releases by natural resource managers in Wisconsin and Michigan aided the spread of E. maimaiga throughout these states. Where it has become established, this acute pathogen has become the dominant natural enemy and has exerted considerable influence in reducing gypsy moth damage. While this pathogen most likely would have invaded these new regions eventually, releases accelerated the spread of E. maimaiga and helped to reduce impacts of initial outbreaks, while further outbreaks were reduced by the pathogen’s subsequent persistence and activity in those areas.

Entomopathogens in the integrated management of forest insects: from science to practice

“…As a result, infected L. dispar larvae have been detected at most release sites, but also at control sites where the fungus was not released. 20 Due to this success, E. maimaiga was introduced in Bulgaria. 54 During 2005-2015, the fungus was isolated in L. dispar in Georgia, Turkey, Serbia, Greece, Macedonia, Slovakia, Hungary, Croatia, and Bosnia and Herzegovina.…”

“…In addition to spraying (inundation biocontrol), a unique inoculation biocontrol application technique was used, in which powder containing conidia was packaged in firecrackers that were thrown over tree canopies, where they exploded and spread the conidia of B. bassiana to infect larvae feeding in the pine tree crowns. 20 The effectiveness of this treatment in practice varies from very low to over 80%. Interestingly, the use of this inoculative control resulted in long-term suppression of the pest (3-5 years).…”

“…Also, we do not consider the use of parasitoids or predators as natural enemies of forest insects, as this has been the subject of much research and several recent review papers. [19][20][21][22] We believe that the complexity of biological communities in forests is one of the most important reasons for the lack of success in applying entomopathogens in these ecosystems, therefore we set two objectives for this review. The first goal was to critically summarize knowledge drawn from the use of microorganisms and nematodes for the control of forest pests, focusing on European species.…”

“…For this reason, we have focused mainly on European insect species, but have also included some examples from North America. Also, we do not consider the use of parasitoids or predators as natural enemies of forest insects, as this has been the subject of much research and several recent review papers 19–22 …”

Biological control of gypsy moth (Lymantria dispar) by the entomopathogenic fungus Entomophaga maimaiga in Bulgaria in 2021

“…Since that time, E. maimaiga has expanded its range by natural spread and artificial introductions in new localities of L. dispar (Solter, Hajek, 2009). Inoculative releases of E. maimaiga accelerate the spread of the pathogen and help to reduce the impact of initial and future outbreaks of the pest (Hajek et al, 2021).…”