Are there viable chemical and non-chemical alternatives to the use of conventional insecticides for the protection of young trees from damage by the large pine weevil Hylobius abietis L. in UK forestry?

Abstract

In UK forestry, the synthetic pyrethroid insecticides alpha-cypermethrin and cypermethrin have been used for many years to provide protection for young trees planted on restock sites from damage by the large pine weevil, Hylobius abietis L. However, concerns over the toxicity of these insecticides to aquatic life if misused have led to a search for alternative forms of protection. This paper describes a detailed programme of efficacy experiments undertaken between 2009 and 2015 to find replacements for these products. Over 50 combinations of chemical and non-chemical approaches were tested on 16 different sites. Of the alternative synthetic insecticides tested, applications of 0.037 g a.i. stem−1 acetamiprid provided high levels of protection from Hylobius browsing damage on young Sitka spruce (Picea sitchensis (Bong.) Carrière) trees, without causing any phytotoxic symptoms, and gave comparable levels of protection to those achievable using alpha-cypermethrin or cypermethrin. Acetamiprid is less toxic to aquatic life than alpha-cypermethrin or cypermethrin and has not been linked to bee decline. Applications of 0.0129 g a.i. stem−1 chlorantraniliprole also showed promise, and this relatively low toxicity non-neonicotinoid insecticide merits further study. Although imidacloprid and thiacloprid also provided good levels of protection, their use in forests is not now permitted due to concerns over their potential impacts on bees and drinking water, respectively. Whilst the natural product insecticide spinosad, and the entomopathogenic fungal control agent Metarhizium anisopliae (Metschn.) Sorokin, gave only limited protection in our work, they may have some future potential if methods of deployment can be improved. Other chemical and non-chemical approaches tested, but found to be largely ineffective in UK conditions, included the natural product insecticides azadirachtin, maltodextrin and pyrethrins, the synthetic insecticides lambda-cyhalothrin and spirotetramat and a wide range of repellents, flexible stem coatings and physical barrier products. However, we conclude that physical barrier sleeves such as MultiPro® and BioSleeve® may have a limited role as a partial substitute for the use of insecticides in the UK in some circumstances, but only if on-site populations of Hylobius are predicted to be low.

Novel Avenues for Plant Protection: Plant Propagation by Somatic Embryogenesis Enhances Resistance to Insect Feeding

“…Damage by pine weevils to planted conifer seedlings is a main threat to successful forest regeneration in large parts of Europe ( Långström and Day, 2004 ; Nilsson et al, 2010 ). Measures to counter this damage, including direct protection of plants with insecticides or protective coatings and various risk-reducing actions, are usually essential ( Nordlander et al, 2011 ; Willoughby et al, 2017 ). Complementary strategies to boost plant resistance and survival rates are currently being investigated, including the induction of plant defenses with the plant hormone methyl jasmonate ( Zas et al, 2014 ; Fedderwitz et al, 2016 ) and enhancing genetically based resistance by selecting parents with low susceptibility from breeding populations ( Zas et al, 2017 ).…”

Acetamiprid, chlorantraniliprole, and in some situations the physical barriers MultiPro® or Kvaae® wax, can be alternatives to traditional synthetic pyrethroid insecticides for the protection of young conifers from damage by the large pine weevil Hylobius abietis L.

“…Nevertheless, given its broad spectrum of control, the fact that it is readily taken up and translocated by plants, and that it is around 500 times less toxic to aquatic life (Willoughby et al 2017), it was thought to be a good candidate for investigation as a potential replacement for pre-planting and top-up spraying of alpha-cypermethrin and cypermethrin. The experiments reported in Willoughby et al (2020) and Moore et al (in prep. ) indicated that acetamiprid showed considerable promise for protecting trees, at least over the first year after tree planting.…”

“…In the UK, a large collaborative research programme took place between 2009 and 2017 involving public forestry administrations across Great Britain, private forestry companies, forest nurseries, and Forest Research scientists. Willoughby et al (2020) and Moore et al (in prep. ) have described some of the results from this programme, and this paper reports on further experiments in the series which examined various potential chemical and non-chemical replacements for alpha-cypermethrin and cypermethrin use in plantation forestry.…”

“…A further low toxicity synthetic pesticide tested in our work was chlorantraniliprole, which is a selective, translaminar, synthetic diamide insecticide acting by contact and ingestion (MacBean 2012). Willoughby et al (2020) concluded that at some restock sites, chlorantraniliprole offered levels of protection comparable to that of traditional synthetic pyrethroid pesticides. Nevertheless, they suggested that further targeted research should be undertaken to understand better how its use could be optimised.…”

“…MultiPro® is a custom-made short cardboard sleeve manufactured in Sweden, fitted around trees either at the nursery or after planting. Willoughby et al (2020) reported that these two products did not consistently provide sufficient protection to be viewed as effective substitutes for insecticides on restock sites with high Hylobius population levels, which are commonplace in the UK and Ireland. However, results were sufficiently promising on sites with low to medium population pressure to warrant further testing.…”