Insecticidal Effect of Entomopathogenic Nematodes and the Cell-Free Supernatant from Their Symbiotic Bacteria against Philaenus spumarius (Hemiptera: Aphrophoridae) Nymphs

Abstract

The meadow spittlebug Philaenus spumarius (Hemiptera: Aphrophoridae) is the primary vector of Xylella fastidiosa (Proteobacteria: Xanthomonadaceae) in Europe, a pest–disease complex of economically relevant crops such as olives, almonds, and grapevine, managed mainly through the use of broad-spectrum pesticides. Providing environmentally sound alternatives to reduce the reliance on chemical control is a primary challenge in the control of P. spumarius and, hence, in the protection of crops against the expansion of its associated bacterial pathogen. Entomopathogenic nematodes (EPNs) are well-known biocontrol agents of soil-dwelling arthropods. Recent technological advances in field applications, including improvements in obtaining cell-free supernatant from their symbiotic bacteria, allow their successful implementation against aerial pests. Thus, this study aimed to evaluate, for the first time, the efficacy of EPN applications against nymphal instars of P. spumarius. We tested four EPN species and the cell-free supernatant of their corresponding symbiotic bacteria: Steinernema feltiae–Xenorhabdus bovienii, S. carpocapsae–X. nematophila, S. riojaense–X. kozodoii, and Heterorhabditis bacteriophora–Photorhabdus laumondii subsp. laumondii. First, we showed that 24 and 72 h exposure to the foam produced by P. spumarius nymphs did not affect S. feltiae virulence. The direct application of steinernematid EPNs provided promising results, reaching 90, 78, and 53% nymphal mortality rates after five days of exposure for S. carpocapsae, S. feltiae, and S. riojaense, respectively. Conversely, the application of the cell-free supernatant from P. laumondii resulted in nymphal mortalities of 64%, significantly higher than observed for Xenorhabdus species after five days of exposure. Overall, we demonstrated the great potential of the application of specific EPNs and cell-free supernatant of their symbiont bacteria against P. spumarius nymphs, introducing new opportunities to develop them as biopesticides for integrated management practices or organic vineyard production.

Exploring the Use of Entomopathogenic Nematodes and the Natural Products Derived from Their Symbiotic Bacteria to Control the Grapevine Moth, Lobesia botrana (Lepidoptera: Tortricidae)

“…The principal challenges facing all agriculture and especially the grape industry are intensive pesticide use, invasion by new pests/diseases, and climate change [11]. Enhancing good practices for pest, disease, and disease vector management would help address these challenges [40,54]. By maintaining the biodiversity of the vineyard agroecosystem, natural enemies of arthropods can contribute to crop protection [55][56][57].…”

“…and Photorhabdus spp. offer promising and environmentally friendly strategies for conventional and organic viticulture worldwide [3,40,58]. Advances in the aerial application of EPNs, the characterization of specific active compounds, and the evaluation of their efficacy and potential risk for other biocontrol agents and the environment will allow the adoption of this technology by growers in a near future.…”

“…Three Xenorhabdus species (X. bovienii, X. nematophila, and X. kozodoii) and Photorhabdus laumondii subsp. laumondii were isolated from their respective mutualistic EPN species (Table 2), following the protocols of Vicente-Díez et al (2021) [40]. Briefly, we first cleaned ~500 IJs of each EPN population by immersion in 5% NaClO for 2-5 min and then washing them with distilled water (three times) before bacterial extraction.…”

“…Finally, we used one of the containers to generate cell-free supernatants (CFS). First, we centrifuged the bacterial suspension at 68.905× g (Thermo Scientific™ Sorvall LYNX 4000 Superspeed Centrifuge, Fisher Scientific SL, Madrid, Spain) for 20 min at 4 • C. Then, the supernatant was filtered through a 0.22 µm sterile pore filter [40]. An aliquot of this filtrate was cultured on NBTA plates in duplicate to verify the absence of bacteria.…”

“…The CFS and UF products obtained from the symbiotic EPN bacteria exhibited high toxicity against the L1 and L3 EGVM instars, arising as novel biotech tools against this particular pest. In the evaluation of the effect against various pests and pathogens, CFS was the most prevalent system [27,40,48,49]. However, Bussaman et al (2009) [50] also showed the potential of UF against the mushroom mite Luciaphorus perniciosus (Acari: Pygmephoridae), also reporting the non-lethal effect of reducing pest fecundity.…”