Development and validation of a simplified morphological identification key for larvae of tephritid species most commonly intercepted at import in Europe

Abstract

Fruit flies (Diptera, Tephritidae) are amongst the most important pests on fruits and vegetables worldwide. All non‐European Tephritidae are listed in Annex I/A1 of Directive 2000/29/EC but only a limited number of species are regularly intercepted in Europe. This study presents a morphological identification key, supported by molecular analysis, for the third‐instar larvae of 10 commonly intercepted taxa. The key proved to be sensitive and specific. However, the evaluation of its reproducibility emphasizes the importance of the operator's taxonomic expertise and questions the relevance of criteria under which a morphological method can be validated. This morphological identification key provides a rapid and economic diagnostic tool for identifying tephritid larvae. It is not intended to cover all species but allows for an initial diagnosis to be made. Given the current difficulty in identifying most immature stages of insects, the approach presented here could be used to develop some morphological identification tools for other species of concern.

PM 7/135 (1) Zeugodacus cucurbitae

“…A: preparation of larvae for observation using a stereo microscope and compound microscope with 3100 magnification (Balmes & Mouttet, 2017) (1) Cut the anterior part of the larva with fine scissors or pins and place it in a 10% potassium solution for 1 h at room temperature or 15-20 min at between 60°C and 80°C; (2) Put the larva in distilled water and flatten the body contents by gentle pressure with a spatula (use a mandrel with flattened fishing thread); (3) Transfer the larva into clean distilled water for several minutes; (4) The larva can be mounted on a slide in a drop of glycerol with a cover slip or prepared for permanent mounting.…”

PM 7/142 (1) Bactrocera latifrons

“…This key can be used for identification to the genus level, but it should be noted that several Ceratitis larvae may also be assigned to the Bactrocera genus using this key. Examination of the 3rd-instar larvae in combination with knowledge about the origin and the host, as well as the evidence provided by previously identified specimens from earlier and similar consignments, may allow a presumptive diagnosis (Balm es & Mouttet, 2017). Kapoor (1993) and Drew & Romig (2016)] (This simplified key will allow the distinction of B. latifrons from most species of agronomic and/or economic importance) 1…”

“…Part A Preparation of larvae for observation using a stereo microscope and compound microscope with 1003 magnification (Balm es & Mouttet, 2017) (1) Cut the anterior part of the larva with fine scissors or pins and place it in a 10% potassium solution for 1 h at room temperature or 15-20 min at between 60 and 80°C.…”

PM 7/134 (1) Dacus ciliatus

“…This key allows identification to the genus level, but not discrimination between different species. Examination of third instar larvae in combination with knowledge about the origin and the host, as well as the evidence provided by previously identified specimens from earlier and similar consignments, may allow a presumptive diagnosis (Balmes & Mouttet, 2017).…”