Woolly apple aphid, Eriosoma lanigerum (Hausmann), is a damaging pest of apple (Malus domestica F.) found in most regions of the world where apples grow. The control of this aphid is becoming increasingly difficult due to changes in pesticide approval in orchards. Forficula auricularia L. is a main predator of E. lanigerum, but the numbers of earwigs in trees are inconsistent and unreliable for control of the pest. This project aimed to test whether annual additions of earwigs in refugia in the tree canopy would reduce E. lanigerum infestations.

In each of three commercial apple orchards with a history of E. lanigerum we introduced, in the spring of each year, commercial predator refuges containing 5 earwigs to each tree in 6 plots (9 trees each) per orchard. The E. lanigerum colonies per plot, aphids per colony, and infested leaf nodes were compared to adjacent plots with no added earwigs or refuges. We also assessed the number of earwigs in refuges at the end of the growing season.

Although in one of the three orchards there was an indication that earwigs placed in refuges in the canopy of apple trees reduced the number of aphid colonies on shoots, this was not statistically significant overall. There were high levels of variation in the numbers of both E. lanigerum and F. auricularia across the 3 orchards and between years. In general, there were fewer E. lanigerum where there were greater numbers of F. auricularia in trees, but the ability of earwigs to control E. lanigerum following two years of introductions was not sufficient alone.

Forficula auricularia contribution to the control of other important orchards pests must not be overlooked. Future research should include identifying the causes of the low and inconsistent earwig numbers in apple orchards.

The study was carried out in three commercial orchards in Kent, UK (Site 1. planted 2018, cv. Braeburn, 51.2959, 1.2449, Site 2. planted 2012, cv. Braeburn, 51.2679, 1.2465, and Site 3. planted 2014, cv. Gala, 51.2964, 1.2478). Malus polliniser trees at Sites 1, 2 and 3 were: Evereste, Red Sentinel and Hilleri; Golden Delicious; and Hilleri and Sentinel, respectively. Tree spacing in the orchards was 1.2 m within the row and 3.5 m between the tree rows.

There were 6 treated (Wignest+ F. auricularia) and 6 untreated plots in each orchard in a replicated block design. Each block was separated by a minimum distance of 8.4 m. Wignests (Russell IPM, UK) containing F. auricularia were deployed in 3 x 3 tree treated plots (9 trees x 6 replicate plots x 3 orchards = 162 Wignests). Wignests (6.5 x 4.0 x 1.5 cm) consisted of or a slatted wooden shelter with a plastic lid and hook for easy placement into trees. Inside the lid was a proprietary earwig food which helps to retain earwigs inside the Wignest for the first few weeks (russellipm.com/product/11622-2/).

Earwigs were collected from Niab East Malling, UK fruit plots, primarily underneath commercially grown strawberry bags, and then housed in 50 x 50 x 50 cm Bugdorms (NHBS) with dried cat food, water, and shelter ad libitum. Earwigs were encouraged into Wignests (total 810) by placing five earwigs in a small (14 cm L x 8 cm W x 6 cm H) ventilated box containing a sugar feeder (plastic pipette bulb and sponge cloth, 5% sucrose solution) and a single Wignest. Earwigs were allowed to enter the Wignests during the day.

Wignests were initially deployed in 2023 on 27/06 (Site 1), 28/06 (Site 2) and 30/06 (Site 3) following a preassessment of E. lanigerum on the trees on the same day. Additional Wignests containing 5 earwigs were redeployed in 2024 on 30/05 (Site 1) and 14/06 (Sites 2 and 3), if previous Wignests contained fewer than 5 earwigs. This totalled 126 Wignest with fewer than 5 earwigs and replacement of 10 Wignests that had dropped from the trees overwinter. Each Wignest was gently (so as not to disturb earwigs) fastened, mid-canopy, to the cane support beside each tree, using a cable tie.

Orchard husbandry followed the normal management program required by the farm. Tree growth stage was recorded at each assessment and spray records were obtained from the host grower.

Eriosoma lanigerum assessments, including the preassessment (27-30/06/2023), followed EPPO (2022) guidelines as described below, on 13/07/2023, 28/07/2023, 03/08/2023 and 23/08/2023, 25/04-03/05/2024, 27/06/2024, 17/07/2024, 26/07/2024 and 22-23/08/2024.

Number of E. lanigerum per colony on bark

Plots of 9 trees were selected that had a minimum of 10 active E. lanigerum colonies for the treated and untreated trees. Thereafter, we searched for 10 E. lanigerum colonies on the bark or old shoots of 9 trees on each plot at each assessment. Wool (white waxy filaments) was blown off each active colony using a compressed air sprayer (Hama Air Duster (400 ml) ASDA), and the number of aphids counted, giving number of aphids per colony.

Number of E. lanigerum colonies on young shoots (leaf nodes)

On the 9 trees in each plot, 25 young shoots (2 - 3 shoots per tree) were selected at random on each assessment. Numbers of leaf nodes with active E. lanigerum colonies were counted per shoot (many were zero). Numbers of aphids per colony were not counted on shoots.

Earwigs in Wignests

On 23/08/2023 (all sites), 30/05/2024 (Site 1), and 14/06/2024 (Sites 2 and 3), and 22/08/2024 (all sites), each Wignest was removed, and earwigs dislodged and counted by tapping into a clear polythene bag before re-releasing at the base of the tree. Wignests were returned to the trees.