Aggregation pattern, sampling plan, and intervention threshold for Pezothrips kellyanus in citrus groves

Abstract

[EN] Pezothrips kellyanus (Bagnall) (Thysanoptera: Thripidae) has recently emerged as an international pest of citrus. It causes severe scarring of the fruit surface and commercial downgrading of fresh fruit production. The goals of this article were to determine the aggregation patterns of P. kellyanus on citrus, to establish an efficient sampling plan to assess their population density, and to develop an environmental economic injury level (EEIL). The study was conducted in 14 citrus groves in Valencia (Spain) during 2008 and in eight citrus groves during 2009. On each grove, population densities of thrips were monitored weekly on citrus flowers and fruitlets during the flowering and fruit setting period. Final damage was determined on developed fruits. Pezothrips kellyanus was the most abundant thrips species, with 73.5% of adults and 92.1% of larvae present, followed by Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), with 18.2 and 3.5%, respectively. First description of first instars of P. kellyanus is provided. Our results prove that thrips show clumped population distributions, with no differences in aggregation parameters between flowers and fruitlets, thrips species, larval stages, or sex of adults. Immature thrips showed a higher aggregation (Taylor's value of b=1.40±0.06) than adults (b=1.19±0.04). Fruit damage by P. kellyanus on developed fruits was strongly correlated with percentage of fruitlets with immature P. kellyanus (r=0.897; n=22). Based on the percentage of fruitlets occupied by immature thrips, the economic injury levels and EEIL were calculated (using chlorpyrifos as insecticide) obtaining values of 7 and 12%, respectively. Insecticide treatments will be necessary if more than 12% of fruitlets are infested by thrips larvae. Constant precision (D=0.25) sampling plans developed show that 200 sample units should be observed in enumerative sampling, and 310 in binomial presence-absence sampling, at population levels of immatures on fruitlets around the EEIL. © 2011 The Authors. Entomologia Experimentalis et Applicata © 2011 The Netherlands Entomological Society.