A brief summary of the impact of control (using Bacillus thurengiensis (Bt) var. kurstaki) of Processionary on biodiversity

Context

Across Britain, the total abundance of larger has declined significantly, by 28%, in the 40 year period from 1968 to 2007. This decline is even greater in southern England with a decline of 40% being recorded (Fox et al, 2013). This decline is indicative of the rapid loss of biodiversity in Britain. This in turn may have substantial impacts on other wildlife and affect the delivery of some ecosystem services, for example pollination. Moths and their are an important component of the diets of many birds, and all Britain’s bats feed on moths to some extent, making up a substantial part of the diet of several species. Moths and their caterpillars are preyed upon by a range of other small mammals. They are also preyed upon by other invertebrates and are unwilling hosts to numerous species of wasp and fly parasitoids, fungi, bacteria and viruses.

Of the c.2,500 species found in Britain, over 200 species are known to feed on oak, with a further three species found within oak galls (Crafer, 2005 & Emmet, 1988). Many other species are found under and around oak trees.

It should also be borne in mind that under the Natural Environment and Rural Communities Act, 2006 every public authority must, in exercising its functions, have regard, so far as is consistent with the proper exercise of those functions, to the purpose of conserving biodiversity.

The following briefly summarises the results of commissioned small scale studies undertaken at Pangbourne, Berkshire, following aerial spraying undertaken in 2013 and another study at Richmond Park, London, in 2013 investigating the impacts on non-target of spraying to control for Oak Processionary. These are followed by very brief notes from a small number of European studies.

1. The Pangbourne (Berkshire) studies

This small scale project was set up following the aerial spraying undertaken in May 2013. As no baseline survey could take place prior to the spraying the project involved a comparative study between two nearby sites, one sprayed the other unsprayed. The study looked at moths, birds and bats, although the bat work was halted at the end of 2013. i. Summary of the findings

 Between June and August 2013 no significant impact on the bat fauna could be detected, although it was noted that it was not possible to draw any more subtle conclusions this early in the monitoring process. (Bioscan Study)

 In the same period there was a general paucity of tit (in particular blue tit) family group activity in sprayed woodland. This could be attributable to a number of factors and may be due to a reduction of favoured invertebrate food resources leading to brood failure due to abandonment or insufficient provisioning of chicks. (Bioscan Study)

 There was an increase in blue tit productivity between 2013 and 2014 within both woods, however, there was a paucity of blue tit and family group activity recorded. In the absence of more specific data on breeding success, it was considered difficult to attribute the lack of family group activity to any one factor. (Ecosulis Study)

 4,722 moths and 372 taxa were recorded in the sprayed wood compared to 7,391 moths and 412 taxa in the unsprayed wood (10 sampling sessions from late June 2013 to end March 2014). Mean abundance and species richness was higher in the unsprayed compared to the sprayed wood. It may be that the unsprayed wood is a richer site, although a spraying impact cannot be ruled out. (Townsend study)

 There is evidence of lower populations of susceptible moth species in the sprayed woodland, with lower populations of Green Oak Tortrix (flying mid May-mid July), loeflingiana (June-August), November Moth group (October-November) and various species of Quaker moths (late February-May) specifically highlighted. A likely explanation for this is the spraying with Bt. (Townsend study)

 The woods were shown to support a range of scarcer species. However, sample sizes were small. In one case, the Square-spotted Clay (former UK Biodiversity Action Plan species), lower numbers were detected in the sprayed woodland. This species could have been a larva in the herb layer at the time of the spraying (2013 being a late season). Conclusions relating to an impact from BT on this group are difficult to draw from the results. (Townsend study) ii. Richmond Park study

Another small scale study was undertaken in 2013 (Freed & Reeve, 2014). As above, no baseline survey could take place prior to the spraying. This study compared three broadly similar areas of oak within the park, one sprayed in May 2013 (A), one in May 2012 (B) and one unsprayed (C). Sampling was arranged in three sessions, late May to early June, late June and late September. The study concentrated on Lepidoptera larvae.

 89 species of Lepidoptera were recorded, 61 of these oak leaf-chewers for all or part of their life history. Several scarce and local species were found.

 The first sample period showed a highly significant difference in abundance and species richness between the three groups following the order A (sprayed 2013) B (sprayed 2012) C (unsprayed) with A being the lowest.

 This result also indicates an impact on both species richness and abundance on group B over a year after spraying.

 The remaining two later in the year samples were also ranked ABC, both samples with a large difference between A and C. This suggests a significant impact a month and four months after the spraying.

 Counts of Green Oak Tortrix were significantly smaller in A & B than C, suggesting that its population had made little recovery a year on from spraying. isertana (flying late May-September) showed a lower count at B than at C. Spring Usher (January-mid March) again followed ABC.

quercana counts followed the order BCA. The larva of this feeds from September to June and it could be that this species has monopolised a niche created following the spraying at B in May 2012. This could hint at a readjustment and change in the lepidopteran community following spraying. iii. European studies

 Roversi et al (2006) found small numbers of dead larvae of non target species throughout the period (one month following spraying) of the study.  Höllrigi-Rosta & Wieck (2013) noted that Bt var. kurstaki was harmful for Lepidoptera larvae. Also noted the use of three control agents (inc. Bt) had an indirect impact of certain birds due to reduced prey availability.  Anon. (2009) noted a decline in two species groups (click beetles and spiders) in the and herb layer through aerial spraying of Bt and Cypermethrin when used to target ‘Frostspanner’ species, e.g. certain Geometridae. This was considered to be an indirect effect due to a decline in prey items. No impact was noted a year after the spraying using a beating sampling technique.

Summary

Combined, the UK studies have indicated a significant impact on a range of non-target Lepidoptera and also that this impact is evident over a year post spraying (further studies will be needed to determine any longer term impact). There was also a hint at a change in the Lepidoptera community in the shorter term, i.e. the species assemblage could be different post spraying. This spraying will also impact on the numbers of larvae reaching adulthood, and from the few examples highlighted above this clearly has a year round effect (it is very likely that Winter Moth and other winter flying geometrids would also be impacted, though no monitoring of their numbers has been undertaken). Therefore, it is reasonable to assume that there will be indirect impacts on predators, parasitoids etc. The evidence from the studies for this indirect impact, however, is less strong, though hinted at by the Pangbourne study and backed by comments in the few European studies documented above.

References

Anon. 2009. Faunistische Begleituntersuchungen zur Klärung der Auswirkungen von Insektizidbehandlungen gegen phyllophage Schmetterlingsraupen in Alteichenbeständen auf die sympatrische Arthropoden fauna. Nordwestdeutshe Forstliche Versuchsanstalt.

Crafer, T. 2005. Foodplant list for the Caterpillars of Britain’s Butterflies and Larger Moths. Atropos Publishing, Holmfirth.

Emmet, A.M. 1988. A field guide to the smaller British Lepidoptera. The British Entomological and Natural History Society, London.

Fox, R., Parsons, M.S., Chapman, J.W., Woiwod, I.P., Warren, M.S. and Brooks, D.R. 2013. The State of Britain’s Larger Moths 2013. Butterfly Conservation and Rothamsted Research, Wareham.

Freed, T.H. & Reeve, N. 2014. A Report of the effects on non-target Lepidoptera of spraying with Bacillus thuringiensis var kurstaki for the control of Oak Processionary Moth in Richmond Park. The Royal Parks, London.

Höllrigi-Rosta, A. & Wieck, S. 2013. Umweltauswirkungen von Bioziden und Pflanzenschutzmitteln zur EPSBekämpfung. In Bräsicke, N. (ed.), Ökologische Schäden, gesundheitliche Gefahren und Maβnahmen zur Eindämmung des Eichenprozessionsspinners im Forst und im urbanen Grün. Julius- Kühn-Institut, Bundesforschungsinstitut für Kulturpflanzen.

Roversi, P.F., Rumine, P. & Barzanti, G.P. 2006. Efficacia di trattamenti aerie con Bacillus thuringensis var. kurstaki per il controllo della pocessionaria della quercia e impatto sulla lepidotterofauna. In Brunelli, A., Canova, A. & Collina, M. (eds.), Giornate Fitopatologiche 2006. Riccione (RN).

M. Parsons Butterfly Conservation April 2015