Evict or infect? Managing populations of the large pine weevil, Hylobius abietis, using a bottom–up and top–down approach

Abstract

Hylobius abietis is the most important pest of replanted coniferous sites in Northern Europe, where feeding by adult weevils can result in up to 100% mortality of seedlings. Field trials were conducted with the aim of reducing H. abietis populations developing in Sitka spruce stumps by increasing pressure from natural enemies (top-down pressure), and reducing the quality of stumps for development (bottom-up pressure). Topdown pressure was applied through inundative treatment of stumps with entomopathogenic nematodes (Heterorhabditis downesi or Steinernema carpocapsae). Bottom-up pressure was applied by treating stumps with the wood colonising fungus Trichoderma koningii. Natural levels of parasitism of H. abietis by the parasitoid Bracon hylobii and the effect of applied agents on B. hylobii were also investigated. Heterorhabditis downesi parasitised more immature weevils than S. carpocapsae, and significantly reduced numbers of adults emerging from stumps compared to controls. Entomopathogenic nematodes did not significantly impact on populations of B. hylobii, and over three sites the effects of both agents were additive. Stumps modified by application of the fungus (bottom-up pressure) did not have fewer H. abietis developing in, or emerging from them; however, development of H. abietis was more advanced in these stumps, and the success of natural enemies was differentially affected. T. koningii facilitated B. hylobii while having the opposite effect on entomopathogenic nematodes, suggesting that it affected the outcome of competition between the nematodes and the parasitoid. #

Environmental safety of entomopathogenic nematodes – Effects on abundance, diversity and community structure of non-target beetles in a forest ecosystem

“…Of the genera recovered in these trials, many are reportedly susceptible to EPN under laboratory and/or field conditions, including: Coccinella (Shapiro- Ilan and Cottrell, 2005), Adalia (Rojht et al, 2009), Altica (Tomalak, 2004), Phyllotreta (Trdan et al, 2008), Otiorhynchus (Lola-Luz and Downes, 2007), Hylastes (Dillon et al, 2008b) and Sitona (Loya and Hower, 2003). It is possible that some individuals from these genera were killed by the applied EPN, but when quantifying risk it is the population, not the individual that is important.…”

Host activity and wasp experience affect parasitoid wasp foraging behaviour and oviposition on nematode‐infected larvae of the forestry pest Hylobius abietis

“…It follows that, if entomopathogens are abundant in the host population, B. hylobii fitness may suffer as unsuitable pathogen-infected hosts are accepted for oviposition when they are still moving (Charnov & Skinner, 1984;Godfray et al, 1991). While natural EPN infection of H. abietis has been reported (Kenis et al, 2004) there is no evidence that this is widespread and natural infections have not been recorded in Ireland to date (Dillon et al, 2006(Dillon et al, , 2008, so there probably is little selective pressure on wild B. hylobii populations to evolve the capacity for EPN detection. The entomopathogenic fungus Beauveria spp., however, is widespread among H. abietis populations on coniferous clearfell sites (Glare et al, 2008;C.…”

Behaviour and Population Dynamics of Entomopathogenic Nematodes Following Application

“…Despite the negative effects of EPN on parasitoids demonstrated in the laboratory, the two types of agent may be compatible in the field, resulting in additive or even synergistic effects (Dillon, Moore, Downes, & Griffin, 2008;Mbata & ShapiroIlan, 2010). A critical feature is the timing of EPN application relative to peak times of susceptible parasitoid stages.…”