First steps towards biological control of the pear gall midge (Contarinia pyrivora) with the insect pathogenic fungus Metarhizium brunneum

Abstract

The pear gall midge Contarinia pyrivora is a serious pest in pear orchards in Europe and in North America (Agriculture and Agri Food Canada, 2013; Muir, 2016). Due to pesticide restrictions and the life strategy of this pest, there is an urgent need for biological control methods in concert with other sustainable control efforts in the pear production systems (Cross et al., 1999, Sigsgaard et al., 2006, Jones et al., 2016). When the images emerge at pre-bloom in spring, after pupation in the soil during winter, they mate, and the females oviposit their eggs in the young buds. The newly hatched larvae start to feed on the pulp from within the developing fruitlets. The larvae continue their growth in the fruitlets (30-40 days). During this time, the infested fruitlets grow rapidly, and eventually fall to the ground (Alford, 2014). The damage caused by the larvae not only results in direct loss of fruits, but the rapid growth also means that the neighbouring fruits are negatively affected by the lack of nutrients available (Jørgensen and Thygesen, 1963). The mature larvae move into the shallow part of the soil (5-10 cm depth) where they overwinter in cocoons before pupating in the spring (Alford, 2014). Lack of control methods is estimated to reduce yield by 50-90%, causing substantial economic losses for the grower (Jørgensen and Thygesen, 1963). In vegetables from Cruciferae, trials have demonstrated control of the closely related Swede midge Contarinia nasturtii using fungi and nematodes (Evans and Hallett, 2016; Evans et al., 2015), but so far no published studies are available for biological control of C. pyrivora. The generalist insect pathogenic fungus Metarhizium brunneum (Hypocreales: Clavicipitaceae) is a good candidate for biological control of C. pyrivora since that fungus exists as commercial products to control different insect pests (Hajek and Eilenberg, 2018). The fungus works well as a biocontrol agent against soil pests, even in combination with other biological control agents (