Tracking mite trophic interactions by multiplex PCR

Flavonoid-producing tomato plants have a direct negative effect on the zoophytophagous biological control agent Orius sauteri

Orius sauteri (Poppius) (Hemiptera: Anthocoridae) is often used for biological control of small arthropod pests in greenhouse vegetable production systems in Asia. In addition to feeding on arthropod prey, O. sauteri consumes small quantities of plant material. Previous studies demonstrated that tomato plant chemistry confers antixenosis resistance to phloem-feeding whiteflies, but the potential nontarget effects of phytochemicals on the beneficial predator O. sauteri are unknown. Comparison of O. sauteri confined to near-isogenic lines (NILs) of tomatoes producing high levels of flavonoids (NIL-purple hypocotyl; resistant to whiteflies) and low levels of flavonoids (NIL-green hypocotyl; susceptible to whiteflies) revealed that O. sauteri had reduced oviposition, nymphal survival, and development on resistant plants, even if they were also provided with prey that did not feed on the host plant. Moreover, O. sauteri showed a significant ovipositional preference in choice assays, laying significantly more eggs on susceptible than on resistant plants. Molecular gut content analysis using the specific chloroplast trnL gene from tomato confirmed that adult and immature O. sauteri feed on both resistant and susceptible genotypes, and feeding behavior assays revealed that resistance did not affect plant feeding or prey acceptance by O. sauteri adults. These results demonstrate a direct negative effect of phytochemicals on a nontarget beneficial species and indicate that resistance mediated by phytochemicals can affect organisms that do not solely feed on phloem sap. The results also indicate that the mode of action and the potential ecological effects of phytochemical-mediated resistance are broader than previously recognized.

DNA Barcoding and Phylogeny of Acari Species Based on ITS and COI Markers

Acari harbor numerous minute species of agricultural economic importance, mainly Tetranychidae and Phytoseiidae. Great efforts have been established by means of recovering morphological, molecular, and phylogenetic traits for species identification. Traditional identification still relies on external diagnostic characters, which are limited and usually exhibit large phenotypic plasticity within the species, rendering them useless for species delimitation and identification. We decided to increase the number of sequences of the Acari mitochondrial COI (Cytochrome C oxidase I) marker and ITS nuclear ribosomal DNA region for species identification in Tetranychidae and Phytoseiidae. The molecular data allow us to establish species boundaries and phylogenetic relationships among several clades of Acari, mainly Tetranychidae and Phytoseiidae. Sequence comparisons between complete COI and the Acari mitochondrial COI, ITS1-5,8S-ITS2, and ITS2 among all Acari sequences have demonstrated that the selected regions, even small, gave enough informative positions for both species’ identification and phylogenetic studies. Analyses of both DNA regions have unveiled their use as species identification characters, with special emphasis on Acari mitochondrial COI for Tetranychidae and Phytoseiidae species in comparison with the Folmer fragment, which has been universally used as a barcode marker. We demonstrated that the Acari mitochondrial COI region is also a suitable marker to establish a barcode dataset for Acari identification. Our phylogenetic analyses are congruent with other recent works, showing that Acari is a monophyletic group, of which Astigmata, Ixodida, Mesostigmata, Oribatida, and Prostigmata are also monophyletic.

Identification of Glycycometus malaysiensis (for the first time in Brazil), Blomia tropicalis and Dermatophagoides pteronyssinus through multiplex PCR

Blomia tropicalis and Dermatophagoides pteronyssinus play an important role in triggering allergy. Glycycometus malaysiensis causes IgE reaction in sensitive people, but is rarely reported in domestic dust, because it is morphologically similar to B. tropicalis making the identification of these species difficult. The identification of mites is mostly based on morphology, a time-consuming and ambiguous approach. Herein, we describe a multiplex polymerase chain reaction (mPCR) assay based on ribosomal DNA capable to identify mixed cultures of B. tropicalis, D. pteronyssinus and G. malaysiensis, and/or to identify these species from environmental dust. For this, the internal transcribed spacer 2 (ITS2) regions, flanked by partial sequences of the 5.8S and 28S genes, were PCR-amplified, cloned and sequenced. The sequences obtained were aligned with co-specific sequences available in the GenBank database for primer design and phylogenetic studies. Three pairs of primers were chosen to compose the mPCR assay, which was used to verify the frequency of different mites in house dust samples (n = 20) from homes of Salvador, Brazil. Blomia tropicalis was the most frequent, found in 95% of the samples, followed by G. malaysiensis (70%) and D. pteronyssinus (60%). Besides reporting for the first time the occurrence of G. malaysiensis in Brazil, our results confirm the good resolution of the ITS2 region for mite identification. Furthermore, the mPCR assay proved to be a fast and reliable tool for identifying these mites in mixed cultures and could be applied in future epidemiological studies, and for quality control of mite extract production for general use.

Plant-feeding may explain why the generalist predator Euseius stipulatus does better on less defended citrus plants but Tetranychus-specialists Neoseiulus californicus and Phytoseiulus persimilis do not

The generalist predator Euseius stipulatus (Athias-Henriot) and the Tetranychidae-specialist predators Neoseiulus californicus (McGregor) and Phytoseiulus persimilis Athias-Henriot play a key role in the regulation of Tetranychus urticae Koch in Spanish citrus orchards. Previous studies have shown that sour orange (Citrus aurantium L.) and Cleopatra mandarin (Citrus reshni hort. ex Tan.) display extreme resistance and susceptibility to T. urticae, respectively. When offered a choice between these two genotypes infested by T. urticae, E. stipulatus preferred Cleopatra mandarin, whereas the specialists did not show any preference. The present study was undertaken to check whether these preferences could be related to the feeding of E. stipulatus on the host plant and/or to differences in prey feeding on the two plants. Our results demonstrate that E. stipulatus is a zoophytophagous mite, which can engage in direct plant feeding in sour orange and Cleopatra mandarin, whereas neither N. californicus nor P. persimilis do so. Whereas Cleopatra mandarin provided a higher-quality prey/feeding substrate for E. stipulatus, which may be related to its phytophagy, no differences were observed for the two specialists. As higher constitutive and faster inducible defense against T. urticae in sour orange relative to Cleopatra mandarin plants result in sour orange supporting lower T. urticae densities and plant damage, our results demonstrate that pest regulation by specialist natural enemies may be more effective when prey feed on better defended plants.