Factors explaining variation in citrus fruit scarring by Pezothrips kellyanus (Thysanoptera: Thripidae)

Abstract: Pezothrips kellyanus, Kelly’s citrus thrips, is a recently recorded citrus pest in southern Australia, New Zealand, Hawaii, Chile and several countries of the Mediterranean Basin. In eastern Spain citrus orchards, P. kellyanus causes important economic losses due to fruit scarring since 2008. Nevertheless, damage by P. kellyanus is highly variable from one geographical area to another and from year to year. The goals of the present study were: (1) to study the changes in abundance of thrips species since the invasion of P. kellyanus in Spain, (2) to elaborate an adequate sampling plan, and (3) to identify possible factors influencing fruit scarring by P. kellyanus. We identified thrips species captured in white sticky traps in 8-19 orchards from 2005 to 2008. Regarding the sampling plan, thrips populations were periodically recorded by sampling citrus flowers and fruitlets in 4-14 citrus orchards from 2008 to 2010. Injury at each grove was obtained directly from the average percentage of fruits with fruit scarring. Finally, we used data of P. kellyanus abundance and fruits damaged by P. kellyanus in 200-1800 orchards from the monitoring networks established by the autonomic Government of the Comunitat Valenciana and by Bayer CropScience between 2005 and 2012. Only four years after its first detection in Spanish citrus, Pezothrips kellyanus represented 85% of thrips species captured in citrus trees, while Frankliniella occidentalis accounted only for 7% of the species captured, suggesting that P. kellyanus has displaced quite rapidly other thrips species in the citrus canopy. We have obtained an Economic Injury Level of 7% of fruitlets occupied by larvae of P. kellyanus. Citrus fruit scarring caused by P. kellyanus varied considerably from year to year and from one geographical area to another. The above variation is likely to be associated with air temperature, the citrus species, and the presence of late maturing varieties in the area. The implications of these factors, together with the soil management and the presence of natural enemies of P. kellyanus, are discussed.