Competition between biological control fungi and fungal symbionts of ambrosia beetles Xylosandrus crassiusculus and X. germanus (Coleoptera: Curculionidae): Mycelial interactions and impact on beetle brood production

Abstract

Ambrosia beetles Xylosandrus crassiusculus and X. germanus are among the most important exotic pests of orchards and nurseries in the US and are difficult to control using conventional insecticides because of their cryptic habits. The use of biological control agents may prove effective by targeting both beetles and fungal symbionts inside tree galleries: entomopathogenic fungi could be used to target beetle foundresses and their brood, or mycoparasitic fungi, e.g., Trichoderma harzianum, could be used to target their associated fungal symbionts. We used a combination of in vitro assays and beetle bioassays to examine competition between symbionts and biological control fungi and the impact of biological control fungi on beetle brood production. The in vitro assays showed T. harzianum outcompeted different strains of Ambrosiella roeperi and A. grosmanniae associated with X. crassiusculus and X. germanus, respectively, whether in primary or secondary resource capture assays. In contrast, entomopathogenic fungi Beauveria bassiana and Metarhizium brunneum blocked the spread of symbionts only in primary competition assays. Complementary beetle bioassays showed that beetle galleries in T. harzianum-treated beech stems had sparse symbiont growth, many with no or only a small number of eggs present. Brood numbers produced by foundresses in T. harzianum-treated stems were comparable to those in stems treated with either entomopathogen at the higher dosages, in which brood reduction was likely due to foundress mortality prior to laying eggs or after laying only a small number of eggs. These results show the potential of using biological control fungi in targeting ambrosia beetle populations either directly by killing foundresses and reducing brood production or indirectly by suppressing symbiont growth in their galleries.

Granulobasidium vellereum (Ellis &Cragin) Jülich, a promising biological control agent

“…This result suggests that the presence of G. vellereum as wood endophyte could prevent the later colonization by wood decay fungi or fungi associated with forest pests. Similar results were obtained by Castrillo et al (2016); in in vitro assays with symbionts of ambrosia beetles they observed that entomopathogenic fungi blocked the spread of symbionts only in primary competition assays, where both symbionts and entomopathogenic fungi were inoculated at the same time. On the other hand, when symbionts were inoculated a week earlier, they overgrew entomopathogenic fungi due to timing of inoculation (Castrillo et al, 2016).…”

“…Similar results were obtained by Castrillo et al (2016); in in vitro assays with symbionts of ambrosia beetles they observed that entomopathogenic fungi blocked the spread of symbionts only in primary competition assays, where both symbionts and entomopathogenic fungi were inoculated at the same time. On the other hand, when symbionts were inoculated a week earlier, they overgrew entomopathogenic fungi due to timing of inoculation (Castrillo et al, 2016). The capacity of G. vellereum to prevent the growth of other fungi as first colonizers can be due to its high rate of growth and the production of abundant asexual spores (Stalpers, 1978).…”

“…However, studies involving biological control of wood decay fungi and pests in forest areas are scarce (Castrillo et al, 2016;Naidu et al, 2015;Schwarze et al, 2012).…”

Permethrin Residual Activity Against Ambrosia Beetle (Coleoptera: Curculionidae: Scolytinae) Attacks Following Field Aging and Simulated Rainfall Weathering

“…Permethrin treatments may be more effective if measured in terms of beetle colonization success, since disruption of fungal pathogen establishment and egg laying ( Hudson and Mizell 1999 , Ranger et al 2016 ), and gallery abandonment have been associated with permethrin treatments ( Schultz et al 2002 , Reding et al 2013 , Reding and Ranger 2018 ). In contrast, Castrillo et al (2016) concluded that unsuccessful colonization could be undesirable if it led to foundress beetles exiting galleries and attacking more adjacent trees or if the female beetle made more attacks on the same tree.…”

Metagenomic approach of associated fungi with <i>Megaplatypus mutatus</i> (Coleoptera: Platypodinae)

“…Previous research has shown that the information provided could offer new tools for pest insect management (Castrillo et al 2016). Megaplatypus mutatus (Chapuis) belongs to the Platypodinae subfamily, whose members along with Scolytinae, are known as ambrosia beetles (Coleoptera: Curculionidae).…”