Development and implementation of season long control strategies for Drosophila suzukii (spotted wing drosophila) in soft and tree fruit

Summary: 

SF/TF 145 was to understand the biology and ecology of Drosophila suzukii (spotted wing drosophila, SWD) in the UK and develop methods for managing SWD to maintain the viability of the UK soft and stone fruit industry faced with a highly invasive and damaging pest.

The project’s original focus was on 
1) Determining the distribution and seasonal population dynamics of all life stages of SWD in different cropping situations on fruit farms in the UK;
2) Developing economically and environmentally sustainable treatment and disposal strategies for soft and stone fruit waste; 
3) Developing and evaluating sampling and extraction methods for quantifying SWD infestations in soft and stone fruits, 
4) Developing a synthetic lure and attract and kill (A&K) technology for incorporation into IPM programmes and  5) Obtaining evidence for the effectiveness of different plant protection products including biopesticides and developing an insecticide resistance management. 

To date, the project has delivered;
• A standardised National Monitoring scheme in collaboration with BGG and JHI, over 4 years, to track the yearly rise of UK SWD populations and phenology through the season (over 130 traps)
• Identification of key habitats, and commercial and wild host plants, of SWD for egg laying and overwintering diapause in the UK
• Identification of 6 other common Drosophila species regularly trapped in the National Monitoring traps; Drosophila obscura group being most abundant and widespread
• Information on SWD entering cherry crops before fruitset; potentially feeding on early nectar sources
• Screening of wild and ornamental fruit for identification of dead-end hosts
• Identification that SWD occurs in blackcurrant crops in the UK and that certain varieties are more vulnerable to SWD egg laying and hence damage (e.g. Ben Hope and Ben Tirran)
• Identification that SWD migrates to sheltered wild winter habitats which typically coincides with leaf-fall in crops
• Confirmation of the timing of onset and cessation of SWD egg laying (generally April until October)
• Egg laying by females in crops was found to be diurnal; peak periods were late morning and evening
• Preference of SWD to lay eggs in ripe fruits compared to over ripe fruits
• Development of a method for eliminating SWD from waste fruit which included sealing waste in air tight containers for 2 or more days to create anoxic conditions
• Evidence on how to dispose of waste so that it does not become another source of SWD infestation, including incorporation into soil or as a 10% mix with a solid waste material
• Data on the most appropriate method for monitoring larvae in the fruit for 4 crops; sugar flotation
• Extensive testing and evaluating of novel and emerging commercially available monitoring traps and baits in comparison to standard Cha-Landolt baits to advise growers
• Conclusion that currently available monitoring traps are not suitable for predicting fruit damage in the crop, but can give an indication of annual population growth and help estimate the efficacy of pesticide sprays
• Development of a ‘dry’ formulation of the Cha-Landolt bait and miniaturisation of sachet for use in attrack and kill (A&K) devices
• Formulation of a dry lure tested at different ratios of the components to further optimise and enhance attraction to SWD, with lower by-catch
• Confirmation that SWD dies within 10 seconds of contact with deltamethrin; improvements to encourage SWD to enter the A&K device, including a clear top, making it comparable to a dry commercial mass trap
• Four potential repellent compounds identified for further testing and the potential to incorporate with A&K in a push-pull control strategy
• Pesticide spray trials on protected strawberry and cherry, and unprotected raspberry, identified approved and novel products that give protection of fruit, with some indication on longevity
• Pesticide testing gave independent information on the frequency of applications needed and led to new approvals being sought for new and biological products for incorporation into spray programmes
• Evaluated the use of sugar as a phagostimulant for enhancement of insecticide treatments in the control of SWD; sugar formulations increased adult mortality, but there was no reduction in fruit damage
• A range of commercial and novel SWD feeding baits were screened for attraction and feeding frequency of SWD, including the addition of yeasts, for future incorporation with insecticides
• Products were tested as egg laying repellents and DS mix (a combination of lime and micronutrients) reduced egg laying in fruit
• Baseline data for SWD susceptibility to key pesticides used in the UK was established to monitor for possible future emergence of resistance.

AHDB growers factsheets on monitoring the pest in fruit and dealing with waste have been produced. Results have been communicated to the Soft and Tree fruit sectors at least once annually and to other UK grower organisations. Web based media for growers have been developed and hosted on the AHDB web site. Training courses through NIAB ARTIS are being delivered.

See related AHDB Factsheet on the use of exclusion mesh

Aim:

This project extension will build on objectives met in SF145 and research from other international projects (see Section 2.1).

The main aim is to provide short to medium term solutions for UK growers which minimise adverse effects to beneficial arthropods in crops and to the wider environment. It aims to reduce the reliance on chemical pesticides for control of SWD. This will lead to reduced residues in fruit and will examine the consequences and side effects of some of the approaches.

Objectives: 

Objective 1. Continued National Monitoring of the populations of SWD in Scotland and England
Objective 2. Develop and optimise a push/pull system using repellents and attract and kill strategies
Objective 3. Develop bait sprays for control of SWD
Objective 4. Investigate prolonging spray intervals for maximum effect but minimal applications
Objective 5. Integrating exclusion netting with other successful controls
Objective 6. Develop, design and communicate a year round strategy for UK crops for SWD control

A further project extension in 2021 (SF 145b), led by James Hutton Institute, used SWD monitoring data from 16 locations spanning 2014-2020 alongside met office data to examine options for modelling with the aim of providing timing guidance data for effective IPM strategies.