DOI: 10.5061/dryad.k6djh9whd
title: European earwig population density surveys and fruit scarring

description: These data were gathered in four successive surveys of ca. 90 blocks of
 commercially produced citrus growing in California's San Joaquin
 Valley.  Data also include two measures of fruit scarring, one
 that involved 'bin samples' (i.e., checks of already-harvested
 fruit in large harvest bins) and one involving checking maturing fruit
 that are still on the trees.
description: <em>European earwig population density
 surveys</em> We manufactured wooden board traps
 to survey 93 commercial citrus blocks, including navel
 oranges, <em>Citrus sinensis</em> (<em>n</em> = 73
 blocks), clementines, <em>Citrus clementina</em> (<em>n
 </em>= 16 blocks), tangelos, <em>Citrus x tangelo
 </em>(<em>n </em>= 2), and mixed varieties (<em>n
 </em>= 2) growing in eastern Tulare and Fresno Counties, CA.  Board
 traps were 25.4 x 25.4 cm squares of OSB (oriented strand board)
 sheathing, 1.82 cm thick; OSB is an inexpensive, engineered wood panel,
 made of small wood strands glued together with waterproof adhesives. 
 Boards were distributed across each block in six locations, at each of
 which three adjacent trees received one board trap each for a total of 18
 boards/citrus block, except for a few very small blocks that received 9
 boards/block.  Boards were deployed in the citrus blocks during February,
 2022, placed under the edge of the citrus canopy, and subsequently visited
 during four time periods in the spring and late fall of 2022 and 2023 to
 count <em>F. auricularia</em> (4-8 April, 2022; 9 February – 2
 March, 2023; 5 – 12 April, 2023; and 23 November – 1 December, 2023). 
 During each survey we counted the total number of <em>F.
 auricularia</em> adults, egg masses (no attempt was made to count
 the number of eggs per egg mass), and aggregations of newly hatched nymphs
 (first and second instars; again, no attempt was made to count the number
 of nymphs per aggregation).  Sampling dates were chosen to focus on times
 of the year when earwigs are present below ground, where they build nests,
 oviposit, and care for their young, or are actively foraging on the ground
 soon after nymphs emerge from their nests.  Citrus fruits are known to be
 vulnerable to <em>F. auricularia</em> herbivory immediately
 after fruit set (‘petal fall’), which typically occurs in late April to
 late May in this region.  A few sites were omitted from some surveys,
 because the sites were actively receiving pesticide applications and could
 not be visited safely. <em>Fruit damage
 estimates</em> In 2022 and 2023 we assessed the
 relationship between <em>F. auricularia</em> densities and
 fruit scarring.  Earwig density estimates were obtained from the survey of
 commercial citrus blocks conducted in April, just prior to the period of
 fruit vulnerability to earwig feeding damage.  We used two estimates of
 fruit scarring.  Our first estimate was derived from ‘bin samples.’   When
 fruit are picked, they are placed in large bins, which are eventually
 loaded onto trucks for transport to the packinghouse.  We inspected the
 visible portions (roughly the top half) of all fruit in the top layer of
 the bins, which typically involved ca. 200-300 fruit, and recorded the
 total number of fruit per bin bearing deep scabby scars.  In 2022 we had
 fruit scarring and earwig density estimates for 33 blocks, based on an
 average of 96.8 ± 108.0 bins checked per block); in 2023 we had fruit
 scarring and earwig density estimates for 30 blocks.  
 We sampled fruit maturing on trees during September 2023, prior
 to the period when splitting of katydid-damaged fruit had been observed. 
 We chose a subset of <em>N</em> = 30 commercial citrus blocks
 that had been surveyed for <em>F. auricularia</em> densities,
 including all blocks that had high earwig densities and a subset of the
 many blocks that had few or no detected earwigs.  In each of these blocks
 we sampled 20 fruit from each of 25 trees located across the block
 (<em>N </em>= 500 fruit total per block) and recorded the
 presence/absence of deep, scabby scars as well as the approximate area of
 the scarred surface.  Scarring generated by insects with chewing
 mouthparts is distinctive and is readily distinguished from other sources
 of scars, including the citrus thrips<em> Scirtothrips
 citri</em>, the common garden snail <em>Cornu
 aspersum</em>, or mechanical processes (e.g., limb rub).
description: # European earwig population density surveys and fruit scarring
 [https://doi.org/10.5061/dryad.k6djh9whd](https://doi.org/10.5061/dryad.k6djh9whd) ## Description of the data and file structure These data were collected for two reasons: (1) first, to characterize the densities of the European earwig generally encountered in commercial citrus groves in California's San Joaquin Valley, and (2) to quantify fruit scarring for maturing or mature fruit that might be generated by European earwigs. Some of the cells are empty. These reflect citrus groves that we were unable to sample on particular dates, usually because of some farming operation that was underway (irrigation, pesticide application, etc.) that would have made sampling dangerous. ### Files and variables #### File: Earwig\_data\_for\_archive.xlsx **Description:**  ##### Variables | Site\_number | Anonymized code for site ID | | :------------------------------------- | :---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | AdultsPerBoardApril2022 | Mean number of adult European earwigs per wooden board trap | | EggClutchesPerBoardApril2022 | Mean number of European earwig egg clutches per wooden board trap | | HatchlingAggregationsPerBoardApril2022 | Mean number of European earwig hatchling aggregations (1st-2nd instars) per wooden board trap | | AdultsPerBoardFeb2023 | Mean number of adult European earwigs per wooden board trap | | EggClutchesPerBoardFeb2023 | Mean number of European earwig egg clutches per wooden board trap | | HatchlingAggregationsPerBoardFeb2023 | Mean number of European earwig hatchling aggregations (1st-2nd instars) per wooden board trap | | AdultsPerBoardApr2023 | Mean number of adult European earwigs per wooden board trap | | EggClutchesPerBoardApr2023 | Mean number of European earwig egg clutches per wooden board trap | | HatchlingAggregationsPerBoardApr2023 | Mean number of European earwig hatchling aggregations (1st-2nd instars) per wooden board trap | | AdultsPerBoardNov2023 | Mean number of adult European earwigs per wooden board trap | | EggClutchesPerBoardNov2023 | Mean number of European earwig egg clutches per wooden board trap | | HatchlingAggregationsPerBoardNov2023 | Mean number of European earwig hatchling aggregations (1st-2nd instars) per wooden board trap | | FruitScarring2022 | Mean number of scarred fruit observed per 'bin sample' (i.e., top layer of fruit visible in a harvest bin); there are approximately 200-300 fruits per top layer of fruit in a single bin | | ProportionFruitScarredSept2023 | Proportion of fruit bearing deep, scabby scars in a sample of 500 fruit taken per commercial citrus block |