Agricultural pest management efforts can be misguided if damage is misidentified. This can lead farmers to unnecessary or excessive control measures, incurring needless costs while failing to suppress damage. Forktailed bush katydids (Scudderia furcata) can leave scars on citrus fruits, rendering fruits unmarketable. These katydids are among the most damaging chewing herbivores of citrus in the San Joaquin Valley. However, recently pest control consultants and famers have become concerned about increasing European earwig (Forficula auricularia) densities in orchards. Earwigs possess chewing mouthparts and are believed to consume young citrus foliage. Based on informal observations, we speculated that earwigs might feed on citrus fruits, generating damage that is mistakenly ascribed to katydids. A database of fruit damage and pest densities derived from various scouting methods from approximately 2,771 field-years (from 2009 to 2012) gathered by consultants and farmers in the San Joaquin Valley was utilized to explore “katydid damage” severity and relationships between katydid and earwig densities and “katydid damage” on fruits. Field experiments in 2018 were conducted to assess whether earwigs damage citrus fruits, evaluate the extent and seasonality of the damage, and compare katydid and earwig damage to examine whether “katydid damage” may be partially due to earwigs.
Results/Conclusions
Analysis of the database revealed that katydids damaged ca. 0.7±0.006 fruit (assessed by examining the top layer of fruit visible in the harvest bin across citrus species). Correlations between katydid densities and “katydid damage” on fruits were low; the correlation coefficient between mean proportion of sampling windows with katydid infestations and the proportion of damaged fruit at harvest was 0.08 (df=342, SE=0.05, P=0.15), suggesting a lack of evidence for a relationship between katydid densities and damage. Katydids are notoriously difficult to sample, but it is also possible that other chewing herbivores may be causing damage mistaken for “katydid damage.” It was observed that some citrus fields with heavily damaged fruits also contained high earwig densities. However, the correlation coefficient between proportion of sampling windows with earwig infestations and proportion of damaged fruit was 0.18 (df=38, SE=0.16, P=0.26); while this correlation is higher than the katydid density correlation, it is also low and non-significant. Yet, this lack of correlation could be due to the low number of earwig density observations. Consultants hardly ever survey earwigs. When they do it is often included only as an aside. This suggests a need for continued research on earwigs as potential citrus pests.