Development of Three Molecular Diagnostic Tools for the Identification of the False Codling Moth (Lepidoptera: Tortricidae)

Three molecular protocols using qPCR TaqMan probe, SYBR Green, and loop-mediated isothermal amplification (LAMP) methods were set up for the identification of larvae and adults of an African invasive moth, Thaumatotibia leucotreta (Meyrick, 1913) (Lepidoptera: Tortricidae). The DNA extracts from larval and adult samples of T. leucotreta were perfectly amplified with an average Ct value of 19.47 ± 2.63. All assays were demonstrated to be inclusive for T. leucotreta and exclusive for the nontarget species tested; the absence of false positives for nontarget species showed a 100% of diagnostic specificity and diagnostic sensitivity for all assays. With the SYBR Green protocol, the Cq values were only considered for values less than 22 (cutoff value) to prevent false-positive results caused by the late amplification of nonspecific amplicons. The limit of detection (LoD) for the qPCR probe protocol was equal to 0.02 pg/µl while a value equal to 0.128 pg/µl for the qPCR SYBR Green assay and LAMP method were established, respectively. The intrarun variabilities of reproducibility and repeatability in all the assays evaluated as CV%, ranged between 0.21 and 6.14, and between 0.33 and 9.52, respectively; the LAMP values were slightly higher than other assays, indicating a very low interrun variability. In order for an operator to choose the most desirable method, several parameters were considered and discussed. For future development of these assays, it is possible to hypothesize the setup of a diagnostic kit including all the three methods combined, to empower the test reliability and robustness.

Development of a loop-mediated isothermal amplification (LAMP) assay for the identification of the invasive wood borer Aromia bungii (Coleoptera: Cerambycidae) from frass

The red-necked longhorn beetle Aromia bungii (Faldermann, 1835) (Coleoptera: Cerambycidae) is native to east Asia, where it is a major pest of cultivated and ornamental species of the genus Prunus. Morphological or molecular discrimination of adults or larval specimens is required to identify this invasive wood borer. However, recovering larval stages of the pest from trunks and branches causes extensive damage to plants and is timewasting. An alternative approach consists in applying non-invasive molecular diagnostic tools to biological traces (i.e., fecal pellets, frass). In this way, infestations in host plants can be detected without destructive methods. This paper presents a protocol based on both real-time and visual loop-mediated isothermal amplification (LAMP), using DNA of A. bungii extracted from fecal particles in larval frass. Laboratory validations demonstrated the robustness of the protocols adopted and their reliability was confirmed performing an inter-lab blind panel. The LAMP assay and the qPCR SYBR Green method using the F3/B3 LAMP external primers were equally sensitive, and both were more sensitive than the conventional PCR (sensitivity > 10³ to the same starting matrix). The visual LAMP protocol, due to the relatively easy performance of the method, could be a useful tool to apply in rapid monitoring of A. bungii and in the management of its outbreaks.

Molecular Identification of Anoplophora glabripennis (Coleoptera: Cerambycidae) From Frass by Loop-Mediated Isothermal Amplification

Anoplophora glabripennis (Motschulsky, 1853), native to eastern Asia, is a destructive woodborer of many ornamental species, leading to the decline and the death of the attacked trees. In outbreak areas as Europe or North America, this pest is usually identified using morphological or molecular analyses of adult or larval specimens. However, the procedures for collecting A. glabripennis specimens from infested plants are too expensive and time consuming for routine screening. A noninvasive diagnostic tool based on frass discrimination is therefore crucial for the rapid identification of A. glabripennis at different development stages in the host. This article describes a rapid diagnostic protocol based on loop-mediated isothermal amplification (LAMP). DNA extracted from A. glabripennis frass was amplified with both visual and real-time LAMP and compared with those of nontarget species. The results show that the method is reliable and accurate and therefore could be a promising diagnostic tool in phytosanitary surveys.

A duplex real-time PCR with probe for simultaneous detection of Geosmithia morbida and its vector Pityophthorus juglandis

The cultivation of walnuts (Juglans sp.) in Europe retains high economic, social, and environmental value. The recent reporting of the Thousand Cankers Disease (TCD) fungus, Geosmithia morbida, and of its vector, Pityophthorus juglandis, in walnut trees in Italy is alarming the whole of Europe. Although Italy is at present the only foothold of the disease outside North America, given the difficulties inherent in traditional identification of both members of this beetle/fungus complex, a rapid and effective protocol for the early detection and identification of TCD organisms is an absolute priority for Europe. Here we report the development of an effective and sensitive molecular tool based on simplex/duplex qPCR assays for the rapid, accurate and highly specific detection of both the bionectriaceous fungal pathogen and its bark-beetle vector. Our assay performed excellently, detecting minute amounts of target DNA without any non-specific amplification. Detection limits from various and heterogeneous matrices were lower than other reported assays. Our molecular protocol could assist in TCD organism interception at entry points, territory monitoring for the early identification and eradication of outbreaks, delineation of quarantine areas, and tracing back TCD entry and dispersal pathways.