Review of the Impacts of Oak Processionary Moth (Thaumetopoea Processionea) Control Methods on Oak Tree Biodiversity
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A Defra Network partnership delivering interdisciplinary plant health FUTURE PROOFING research to improve biosecurity and build capability Plant Health Work Package 5: Control Task 5.3: OPM Control Review of the impacts of Oak Processionary Moth (Thaumetopoea processionea) control methods on oak tree biodiversity Rachel Down and Neil Audsley 31st March 2018 Table of contents Abstract ……………………………………………………………………………………………………………………………………. 3 Chapter 1. Introduction ……………………………………………………………………………………………………………. 4 Chapter 2. Relative toxicities of Bacillus thuringiensis var. kurstaki, diflubenzuron and deltamethrin to Lepidoptera and other invertebrates …………………………………………….. 7 Chapter 3. Invertebrate assemblages associated with oak trees ……………………………………………… 32 Chapter 4. Evaluation of methods for monitoring oak tree invertebrate biodiversity ……………… 66 Chapter 5. A review of similar studies: Short and long-term impacts of tree insecticides on invertebrate biodiversity and the wider environment ……………………………………… 72 Conclusions ………………………………………………………………………………………………………………………….…. 91 Recommendations ……………………………………………………………………………………………………………….…. 93 References ……………………………………………………………………………………………………………………………… 95 Appendix 1. List of Lepidoptera whose larvae feed on oak at some point between April and June ……………………………………………………………………………………………………………………………….. 106 Appendix 2. IUCN Red Data Book (RDB) categories and criteria ………………………………………….. 109 2 Impact of OPM control methods on oak tree biodiversity | March 2018 Abstract Oak processionary moth Thaumetopoea processionea L. (Lepidoptera: Thaumetopoeidae) is an alien invasive species that was first introduced to the UK circa 2005, and which poses a threat to native oak trees (through defoliation) and human health due to the tiny urticating hairs on the larval exoskeletons, which when shed can cause allergic reactions including skin rashes, eye and throat irritations, and breathing difficulties in susceptible individuals. As such there is a requirement that populations of this invasive pest are controlled. At present there are several control methods approved for use in the UK including three insecticide sprays: the bacterial biopesticide Bacillus thuringiensis var. kurstaki (DiPel® DF), the insect growth- regulator diflubenzuron (Dimilin® Flo), and the synthetic pyrethroid deltamethrin (Bandu®), as well as physical nest removal. There are two species of oak native to the British Isles, the pedunculate (common) oak Quercus robur L. and the sessile oak Q. petraea (Matt.) Liebl., and both support a vast array of species, providing an important food source for many species, and habitat for others. To date, over 2000 species of mosses, lichens, fungi, invertebrates, birds and mammals are known to be associated with oak, with over 800 invertebrate species associated with Q. petraea and over 1000 species of invertebrates associated with Q. robur. In particular, the invertebrate species could be directly at risk of non-target impacts from pesticides that may be applied to oak to control a pest species, therefore it is important to investigate and assess these potential non-target impacts. It is likely that there are in the region of 150-200 species of native Lepidoptera (potentially more) that feed on oak, and a significant proportion of these are present as larvae, feeding within the oak tree canopy, at the same time as oak processionary moth larvae, and therefore at risk of non-target impacts. This review uses currently available literature to gather evidence on the potential impacts of the three insecticides currently approved to control oak processionary moth on invertebrate biodiversity within a tree environment, and to a lesser extent, implications for the wider environment by providing a detailed review on the mode of action, toxicology, specificity, mobility and persistence for each of the active ingredients. The review also seeks to collate detailed life-cycle and habitat information for the lepidopteran species associated with oak to establish which species are likely to be directly impacted upon by any insecticidal treatment. 3 Impact of OPM control methods on oak tree biodiversity | March 2018 Chapter 1. Introduction The oak processionary moth Thaumetopoea processionea L. (Lepidoptera: Thaumetopoeidae) is a species that is native to central and southern Europe and was first introduced into the London area of the UK as an invasive species circa 2005, almost certainly as eggs present on plants imported from continental Europe (CABI, 2018; Forestry Commission, 2018a). It has since spread to neighbouring counties (Surrey, Essex, Hertfordshire, Buckinghamshire, and west Berkshire) (Forestry Commission, 2018a). The larvae of oak processionary moth feed on the foliage of oak and cause significant defoliation in Europe; this can leave a tree weakened and therefore vulnerable to other threats (Forest Research Advisory Note; Forestry Commission, 2018a). As such this invasive species poses a threat to the UK native oak species, the pedunculate (common) oak (Quercus robur L.) and the sessile oak (Quercus petraea (Matt.) Liebl.) as well as the introduced Turkey oak (Quercus cerris L.) (Forestry Commission 2018b). Oak processionary moth is most often found on urban trees, along forest edges and in amenity woodlands (Forestry Commission 2018b). It is reported that other species of tree such as hornbeam, hazel, sweet chestnut, beech and birch can also be attacked by oak processionary moth, most notably when they are adjacent to severly defoliated oak trees (Forestry Commission 2018b). Oak processionary moth also poses a threat to human and animal health because the larvae produce tiny urticating hairs, which when shed can cause allergeric reactions, evident as skin rashes, eye irritations (such as conjunctivitis), sore throats (pharyngitis) and breathing difficulties (including asthma) in susceptible people that come into contact with them (Forestry Commission, 2018a,b). Contact with these tiny hairs is through direct contact with the caterpillars and with the nests, which contain huge numbers of shed hairs, but also occurs because these tiny hairs break off very easily and get dispersed in air currents (Forestry Commission, 2018a,b). 1.1 Biology Eggs are laid in single layer rows, forming a plaque which is then covered with greyish scales, on twigs and small branches within the canopy from July to early September (Forestry Commission 2018b). Larvae hatch from the eggs the following April (sometimes earlier) and feed gregariously on the foliage from April to June, moving down the tree as they get larger (Forestry Commission, 2018a,b). When they are not feeding they rest in white, silken webbed communal nests found on the trunks and branches (only very rarely among the leaves), anywhere from ground level to high up in the tree (Forestry Commission, 2018a,b). Nests can vary enormously in size, from the width of a 50p coin to several feet (Forestry Commission, 2018a). When travelling between nest and feeding site, the lavae follow one another forming processions. Larvae typically complete their development, passing through six larval instars, in 9-12 weeks; they pupate within the nests and adult moths emerge one to two weeks later, sometimes up to four weeks later (Forestry Commission, 2018a,b). 4 Impact of OPM control methods on oak tree biodiversity | March 2018 1.2 Control As an invasive pest species, and because of the threat it poses to both oak and human health, oak processionary moth is under surveillance, monitoring and control in the UK. There are currently three management zones for oak processionary moth: the Core Zone, the central part of the London outbreak area; the Control Zone, the buffer area; and the Protected Zone, which is free of the pest and where incursions must be eradicated by law (Forestry Commision, 2017). The government-funded oak processionary moth control programme (OPMCP) has been running since 2013; this currently enforces and/or carries out management of oak processionary moth in the Control and Protected Zones; management in the Core Zone is the responsibility of individual landowners (Forestry Commission, 2017). There are several possible methods for controlling oak processionary moth in the UK including nest removal and three currently approved insecticides sprays: the insect growth- regulator diflubenzuron (Dimilin® Flo) (MAPP 11056), the broad-spectrum synthetic pyrethroid deltamethrin (Bandu®) (MAPP 16153) and the bacterial biopesticide Bacillus thuringiensis var. kurstaki (DiPel® DF) (MAPP 17499). Bacillus thuringiensis var. kurstaki (Btk) is currently the preferred option as it is considered the most selective of the three insecticides (ADAS UK Ltd, 2015) and is the method normally used in the OPMCP, although sometimes Dimilin® Flo will be used (OPM Management, 2017). Both B. thuringiensis var. kurstaki and diflubenzuron are most effective against very young larvae, so timing of application is crucial (Forestry Commission, 2017). Whilst there were no plans to use deltamethrin within the OPMCP in the 2017-2018 season, its use may be considered in the Protected Zone as part of a robust response package (OPM Management, 2017) or by private landowners in the Core Zone; it may be the preferred insecticide against older larvae in circumstances when use of an insecticide is considered better than nest removal (Forestry Commission, 2017). Oak processionary moth management guidelines were provided within the TH0102 Project Final Report (ADAS UK Ltd, 2015). These include: 1. Spray