Review of Control Options for Suppression Or Elimination of the Yellow-Legged Asian Hornet, Vespa Velutina Nigrithorax in the UK
Total Page：16
File Type：pdf, Size：1020Kb
Review of control options for suppression or elimination of the Yellow-legged Asian hornet, Vespa velutina nigrithorax in the UK. Project PH0530 Ben Jones, Kirsty Stainton and Maureen Wakefield March 2017 Contents 1. Control of invasive species .................................................................................. 3 2. Vespa velutina nigrithorax ................................................................................... 4 3. Monitoring, trapping and mechanical control ....................................................... 6 4. Chemical control of Vespa velutina nigrithorax .................................................... 7 4.1 Chemical control agents ................................................................................ 7 4.2 Formulation types available .............................................................................. 9 4.3 Pheromones ...................................................................................................... 9 4.4 Toxic baits against Vespids ............................................................................... 9 5. Biological control of Vespa velutina nigrithorax.................................................. 14 6. Novel control techniques for control of Vespa velutina nigrithorax .................... 16 6.1 Sterile Insect Technique.................................................................................. 16 6.2. RNA interference ........................................................................................... 21 6.3 Genetic transformation and Genome editing .................................................. 24 7. Conclusion and recommendations ..................................................................... 28 8. References ........................................................................................................ 31 1. Control of invasive species When a new species is introduced into an area where they are not indigenous, they may be referred to as ‘non-native’, ‘exotic’ or ‘alien’ (Manchester, 2000). Only approximately 10% of introduced species will become established in their new territory and only 0.1% will become invasive (Manchester, 2000). Invasiveness refers to the ability of a non-native species to be detrimental to the economy or ecosystem into which it has been introduced and may be used synonymously with the term ‘pest’. The chances of eradicating, or suppressing, an invasive population once it has become established in its new territory is very low. Once established a pest population can be time-consuming and costly to control (Manchester, 2000). There are 34 recorded species of introduced Vespidae around the world, the most invasive of which are eusocial, like the yellow-legged Asian hornet Vespa velutina nigrithorax (Beggs et al., 2011). Vespidae are generalist feeders with a high dispersal potential and fast reproductive rate which accounts for the success of the invasive Vespids, such as Vespula germanica and Vespula vulgaris, across North America, New Zealand and Australia (Beggs et al., 2011). Traditional control methods can be broadly characterised as physical/mechanical, chemical or biological in nature. Physical/ mechanical control may involve trapping or manual destruction of an invasive pest, through hunting for example. Chemical control may involve the use of broad spectrum insecticides. Biological control usually refers to the introduction of biological agents, such as predators, parasites or pathogens of the target species. In the past two decades, molecular techniques have also been developed and deployed for pest control; this includes genetic modification, para- transgenesis and the use of RNA interference (RNAi). This review will include an evaluation of the techniques described above and their applicability for use against the yellow-legged Asian hornet, Vespa velutina nigrithorax. The review will conclude with a summary of these techniques and the feasibility of using them, and a recommendation of the likely most effective techniques as well as a description of further research that may be required to improve the suite of control options available. 2. Vespa velutina nigrithorax Vespa velutina is a species of hornet native to East Asia. It belongs to the order Hymenoptera which includes bees, wasps and sawflies; hornets are closely related to wasps, which all belong to the family Vespidae (Figure 1). There are 12 subspecies of V. velutina across its native range, which can be identified by their thoracic and abdominal colourations (Perrard et al., 2014). The dark subspecies nigrithorax was discovered in southern France in 2004 after an accidental introduction and was found to originate from a hornet population from eastern China using genetic analyses (Arca et al., 2015). These analyses determined that the incursion was initiated by very few or perhaps even a single female queen hornet that had mated with multiple males (Arca et al., 2015). Despite the strong population bottleneck experienced by this invasive species and its resulting restricted genetic diversity, V. velutina nigrithorax has gone on to colonise approximately three quarters of France (Villemant and Rome, 2016), northern Spain in 2010, Portugal and Belgium in 2011, Italy in 2012 (Darrouzet et al., 2015 and Lopez, 2011), Germany in 2014 (Orlov, 2016). At the time of writing of this report (March 2017) there had been a single incursion of V. velutina nigrithorax in the UK. A nest was subsequently found and destroyed. Figure 1: Basic representation of relatedness of hornets to bees and wasps. A review of control techniques will not be complete without an introduction to the biology of V. velutina; aspects of the biology must be understood when considering the merit of each control option. Some pest control strategies involve targeting the reproductive individuals and one of the crucial differences in V. velutina biology that sets them apart from other pest insects is its sex determination system. The haplo- diploid species V. velutina has a single-locus complementary sex determination system; females are heterozygous at a sex-determining locus, while males are homozygous (diploid) or hemizygous (haploid) (Darrouzet et al., 2015). A colony of V. velutina is comprised mainly of non-reproductive female workers. The only reproductive female in the colony is the queen (although workers may be able to lay haploid eggs). Hornet nests only produce reproductive individuals in autumn, the queen will first begin by laying eggs destined to become males followed, weeks later, by female eggs destined to become the future queens or gynes. In France, males begin emerging in late August and virgin queens in early/mid-September, they mate and the females disperse (this may occur just before or just after hibernation) while the males die (Darrouzet et al., 2015). Three times as many males as virgin queens are produced by a nest (Monceau et al., 2013a). In early spring (late February onwards), mated queens emerge to find sites for nest- building (Villemant and Rome, 2015). Between 90 and 99% of V. velutina queens die of natural causes before making a nest due to over-wintering losses and fierce competition among queens for nesting sites. Even if an intervention is able to remove the majority of new queens from an environment (i.e. through trapping) the effects of density dependent competition for this species are yet to be ascertained so the effectiveness of control at this stage is unknown (Monceau and Thiéry, 2016). Vespa velutina has a long-distance dispersal potential with a rate of spread of 78 km per year in France; this is in part due to their excellent flight ability, as queens can travel up to 200 km in 10 days (Robinet et al., 2016). However, their spread is also hastened by the inadvertent transport of queens via human activity (Robinet et al., 2016). This makes prediction and prevention of novel incursions extremely difficult. Vespa velutina is a univoltine species, i.e. it has only a single generation each year. The successful queen will create her primary nest and rear her first set of brood alone; when this brood emerges they abscond from the primary nest and build a secondary nest. The secondary nest is managed by the workers and a single nest may produce up to 13,000 workers in a season, with approximately 1800 individuals present in the nest at a given time (Villemant and Rome, 2015). In France 70% of secondary nests are found above 10m and they may be found equally in urban (49%) or agricultural and forested areas (50%) (Villemant and Rome, 2015). The majority of nests will be located in trees and largely undetectable by sight. The difficulty involved in detecting nests is a significant obstacle for control. Detection methods have recently been reviewed in the Defra funded project PH0524 (Review of the potential detection and control options for nests of the Asian hornet (Vespa velutina nigrithorax)) and will not be considered further in the current review. When considering the methods for control of an organism, an understanding of the life history and reproductive biology of that organism is crucial and any attempt to control will be unsuccessful without it. This will be especially true for Vespa velutina nigrithorax, as its life cycle, reproductive strategy and biology differ somewhat from the majority of canonical ‘pest’ insects. Most pest insects belong to the orders Diptera (i.e. mosquitoes, Medfly, Screwworm), Coleoptera (i.e. Colorado potato beetle, boll weevil) and Lepidoptera (i.e. codling moth,