Feeding behaviour and mortality of Philaenus spumarius exposed to insecticides and their impact on Xylella fastidiosa transmission

Abstract

BACKGROUND Insecticides are essential, though controversial tools in modern pest management. Insecticides can slow the spread of key vector‐borne plant pathogens, but often lead to inconsistent results given that insecticide use is generally focused on acute toxicity under no‐choice conditions. Here, we analysed the lethal (survival) and sublethal (feeding behaviour) effects of six commercial products (acetamiprid, deltamethrin, spinosad, sulfoxaflor, pyrethrin and kaolin) on Philaenus spumarius, vector of the bacterium Xylella fastidiosa. Furthermore, we assessed the impact of insecticides displaying different degrees of acute toxicity against spittlebugs (highest to lowest: acetamiprid, pyrethrin and kaolin) on the transmission of X. fastidiosa by P. spumarius under both free‐choice and no‐choice conditions. RESULTS Deltamethrin, acetamiprid and to a limited extent pyrethrin significantly altered the feeding behaviour of P. spumarius. Deltamethrin and acetamiprid were highly toxic against P. spumarius, but the mortality induced by exposure to pyrethrin was limited overall. By contrast, spinosad, sulfoxaflor and kaolin did not significantly impact P. spumarius feeding behaviour or survival. Under no‐choice conditions, both pyrethrin and acetamiprid reduced the X. fastidiosa inoculation rate compared with kaolin and the control. On the other hand, pyrethrin reduced transmission, but acetamiprid failed to significantly affect bacterial inoculation under free‐choice conditions. CONCLUSION Pyrethrin was the only compound able to reduce X. fastidiosa transmission under both free‐choice and no‐choice conditions. Xylella fastidiosa management strategy based exclusively on the evaluation of insecticide acute toxicity under no‐choice conditions would most likely fail to prevent, or slow, bacterial spread. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

<em>Xylella fastidiosa</em> Dispersion on Vegetal Hosts on Demarcated Zones in the North Region of Portugal

“…Following a dormancy period of around 100 days, the eggs hatch in early spring. The nymphs then progress through five developmental stages over 5-8 weeks, all the while enveloped in a protective mucilaginous foam [51]. Adults usually emerge in April or May and engage in mating during early summer, after which they tend to linger in the nearby vegetation [48].…”

Innovations towards sustainable olive crop management: a new dawn by precision agriculture including endo-therapy

“…Whilst injection of insect-controlling active ingredients into olives may even result in repelling effects that would significantly interfere with uptake and transmission of bacterial diseases, it is noteworthy that the successful transmission of X. fastidiosa by spittlebugs requires only a few minutes, thus may happen rapidly even in the presence of a repellent ( Cornara et al., 2020 ). Finally, X. fastidiosa vectors can thrive on many other plant hosts present in proximity to olive trees, thus generating a free-choice situation that may significantly impact the efficacy of insecticides ( Lago et al., 2022 ). With this in mind, targeted delivery of crop protection products using innovative endo-therapy can play an important part in IPM of olive orchards.…”

Xylella fastidiosa: A Glimpse of the Portuguese Situation

“…After a diapause period of approximately 100 days, the eggs hatch in early spring. The nymphs then progress through five developmental stages over a period of 5-8 weeks, during which they remain covered by a protective mucilaginous foam [40]. Adults typically begin to emerge in April or May and start mating during early summer, after which they tend to remain in the surrounding vegetation [41].…”

“…However, it has been discovered that nymphs lose their infectivity after ecdysis, or molting. During this process, there is an exchange of the buccal armor where the bacteria are attached, and they are subsequently eliminated [21,40]. To reacquire the bacteria, the new adults will need to feed on an infected plant.…”

“…According to Altamura et al, acetamiprid is highly toxic against Philaenus spumarius [114]. However, some authors have suggested that this neonicotinoid does not have a significant impact on bacterial inoculation, as the vectors treated with this insecticide showed less vulnerability to it compared to other insecticides [40]. Bethke et al also reported the effective insecticidal action of a neonicotinoid in reducing insect vectors in California [115].…”