PCR-based detection of prey DNA in the gut contents of the tiger-fly, Coenosia attenuata (Diptera: Muscidae), a biological control agent in Mediterranean greenhouses

The tiger-fl y Coenosia attenuata Stein (Diptera: Muscidae: Coenosiini) is a generalist predator that preys on several pests of greenhouse crops and is considered a biological control agent in the Mediterranean region. Previous behavioural observations identifi ed its preferred prey, but a more in-depth evaluation will benefi t from using Polymerase Chain Reaction amplifi cation of prey DNA remains in the gut of this predator. To evaluate the rate of decay and suitability of this method for use in the fi eld assessments, we carried out a laboratory feeding calibration experiment on 355 females of C. attenuata, which were killed at different intervals of time after ingestion (10 time points from 0 to 48 h). The prey species tested were: Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae: Trialeurodini), Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae), Diglyphus isaea (Walker) (Hymenoptera: Eulophidae: Cirrospilini), Bradysia impatiens (Johannsen) (Diptera: Sciaridae) and Drosophila mercatorum Patterson & Wheeler (Diptera: Drosophilidae: Drosophilini). Based on a probit model, amplifi cation success of prey DNA declined exponentially with increasing time after ingestion. The half-time molecular detection differed between species, ranging from an average of 5 h for T. vaporariorum and D. isaea, 6 h for B. impatiens, 15 h for L. huidobrensis to more than 40 h for D. mercatorum. This study confi rmed the feasibility of using DNA based detection to identify prey species in the gut contents of C. attenuata and provided calibration curves for a better understanding of predation activity in this agroecosystem. * Present addresses: S.G. Seabra – Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, Rua da Junqueira no 100, 1349-008 Lisboa, Portugal; J. Martins – Ascenza Agro, Lda., Alameda dos Oceanos 1.06.1.1, 1990-207 Lisboa, Portugal; I. Freitas – CIBIO/InBIO, Research Center in Biodiversity and Genetic Resources of the University of Porto, Vairão, Portugal INTRODUCTION Generalist invertebrate predators may be important biological control agents against crop pests, as shown in a number of manipulative fi eld experiments (Symondson et al., 20 02). When considering introducing or enhancing a particular generalist predator species for pest control, its prey preference and effect on pests (target) and non-pests (non-target) should be studied (Stilin & Simberloff, 2000; Louda et al., 2003), even when native control agents are considered (Howarth, 2000). Field observations of predator preferences are not always feasible and molecular anaEur. J. Entomol. 118: 335–343, 2021 doi: 10.14411/eje.2021.035