Detection and characterization of incidental vibrations from Drosophila suzukii in infested fruits

The spotted-wing drosophila (SWD), Drosophila suzukii (Matsumura), is an invasive species native to East Asia and now widespread worldwide. Major economic damage is caused by the larvae developing within ripening soft-skin fruit. Currently, larval detection in fruit is limited to destructive methods and post-harvest control strategies heavily rely on the use of chemicals or cold to inhibit egg eclosion and larval growth. Feeding larvae are likely to induce substrate-borne vibrations in the berry that could be exploited as cues by predators or to develop a non-invasive pest detection method, an approach previously applied on leaves and wooden structures, but never on fresh fruit. We used a laser vibrometer to detect and characterize the incidental vibrations produced by D. suzukii larvae within fresh blueberries at five different pest age (48, 96, 168, 216 and 264 h). An innovative statistical analysis was performed to assess if infestation level (number of pupae) and pest age (hours after exposure) affect the spectrum and the amplitude of vibrations. The recordings of infested berries were characterized by the presence of a series of broad-band pulses (frequency range 0.1–2 kHz) without a regular temporal pattern, in an amplitude range between 12.1 and 946 μm/s. Furthermore, the analysis revealed the possibility to distinguish between different pest ages and infestation levels. By a spectral analysis of the recordings, the pest ages can be distinguished among each other, but for the age groups at 168 and 216 h after infestation. The vibration amplitude trend gradually increased up to 168–216 h after infestation, and then decreased until fly emergence. Low-infested blueberries showed a faster D. suzukii development time compared to high-infested blueberries. This was reflected into vibrational recordings, as low-infested blueberries exhibited peak amplitude at earlier stage compared to high-infested ones. Results suggest that D. suzukii larvae induce detectable vibrations by feeding within berries that are dependent on infestation level and pest age. We discuss the possible ecological role of such vibrations as cues for unintended receivers, such as predators and parasitoids, and their potential for innovative infestation detection method

Non-target effects of neurotoxic insecticides on Ganaspis cf. brasiliensis, a classical biological control agent of the spotted wing Drosophila

Background The spotted wing drosophila, Drosophila suzukii, is an invasive pest causing significant economic losses worldwide. Current pest control strategies mainly rely on insecticides, which negatively impact fruit marketability and the sustainability of integrated pest management (IPM) programs. In addition, pesticides can have dramatic consequences on non-target species when persisting in the environment at low concentrations after field applications. In this context, chemical control can strongly interfere with the releases of the G1 strain of the Asian larval parasitoid Ganaspis cf. brasiliensis, which is currently the adopted classical biological control agent to manage D. suzukii infestations worldwide. Methods Probit analysis was used to assess the baseline toxicity of acetamiprid, cyazypyr, lambda-cyhalothrin, phosmet, and spinosad on G1 G. cf. brasiliensis adults through residual contact exposure in the laboratory. Then, adult parasitoids were exposed to insecticide low Lethal Concentrations (LC5 and LC30) and their mortality was checked daily to assess the survival of treated wasps. Results Lambda-cyhalothrin showed the highest toxicity on the parasitoid with a LC50 of 1.38 × 10–3 g active ingredient (a.i.) /L, while cyazypyr seemed the safer active ingredient with an estimated LC50 of 0.20 g a.i./L without affecting parasitoids at sublethal doses. Spinosad and phosmet significantly reduced wasp survival at both LC30 and LC5, while lambda-cyhalothrin and acetamiprid affected parasitoid lifespan only at LC30. Spinosad, lambda-cyhalothrin and phosmet LC30 caused the major survival reductions, followed by acetamiprid LC30. The least significant reduction in parasitoid survival was 21.6% by spinosad LC5. Conclusions Overall, this study highlighted the importance of carefully selecting insecticides to minimize adverse effects on non-target organisms. In particular, cyazypyr was the most promising candidate to integrate inoculative biological control with chemical treatments. By contrast, the application of phosmet, spinosad and lambda-cyhalothrin should be avoided alongside parasitoid field releases. Although acetamiprid is less used against D. suzukii in the field than the other tested molecules, it should be used with caution due to its sublethal toxicity on the parasitoid. These results provide the first evidence of G. cf. brasiliensis susceptibility to insecticides in order to promote sustainable and efficient pest management strategies

Effects of irradiation on biology and mating behaviour of wild males of brown marmorated stink bug using a 6 MV medical linear accelerator

The brown marmorated stink bug, Halyomorpha halys, is a pentatomid bug of Eastern Asian origin that became an economically relevant pest in the Eurasian and American continents. Management of this species is limited to use of chemical insecticides: an inefficient method due to the strong adaptability of the target pest. The sterile insect technique (SIT) is potentially a valid tactic in the search for nontoxic alternatives. In this work, we investigated the suitability of masstrapped overwintering males, collected during the aggregation phase before the winter diapause, for their release as competitive sterile males in an SIT programme. Differently from previous studies, irradiation was applied with a linear accelerator device that produced high-energy photons. Following a similar scientific protocol with newly emerged irradiated males, the effects of X-ray irradiation on physiological parameters (longevity, fecundity and fertility) were assessed. In addition, behavioural bioassays were carried out in no-choice conditions to evaluate if irradiation interferes with mating processes. The results are very encouraging; the effects of the irradiation at 32 Gy did not differ from the controls in the longevity or fecundity of the exposed overwintering adults. The hatching rate of the eggs laid by the fertile females that had mated with the irradiated males was less than 5%. The results of behavioural bioassays showed that the irradiation did not cause a significant impact on the quality of the sterile males. More research is warranted to evaluate the mating competitiveness of sterile males in semi-field and field condition

Foraging behavior of Ganaspis brasiliensis in response to temporal dynamics of volatile release by the fruit–Drosophila suzukii complex

The lineage G1 of Ganaspis brasiliensis is a larval parasitoid of the worldwide pest Drosophila suzukii and one of its most effective natural enemies in the native area. Because of its high degree of host specificity, G. brasiliensis G1 is considered a suitable species for introduction in areas invaded by D. suzukii following a classical biological control approach. Indeed, the release of the parasitoid is currently implemented in the USA and Italy. G1 females attack only host larvae developing in ripening fresh fruits on the plant and not larvae that develop in decaying fruits. To date, virtually no information is available on the cues regulating the foraging behavior of G1. In this study, we therefore aimed to find out whether chemical cues are exploited by G1 females to: (i) locate host fruits; (ii) locate suitable host larvae within infested fruit; (iii) discriminate between infested fresh fruits and infested rotting ones. We used a model system composed of blueberries and D. suzukii tested in two-choice olfactometer bioassays (with D. suzukii-infested fruits, healthy fruits, and pure air as odor targets), followed by the collection and the characterization of volatile organic compounds (VOCs) released by the tested targets. The results showed a clear time-dependent choice made by G1 females of infested versus healthy fruits related to the concomitant development of D. suzukii larvae and fruit degradation. Attraction to infested fruits was recorded during the early stages of infestation, followed by a repellent phase coinciding with fruits largely degraded by larval feeding. We found that the attractiveness of G. brasiliensis G1 towards fruits infested by young larvae was associated with the detection of VOCs released by the infested blueberries, and host’s cuticular hydrocarbons. Conversely, the repellence of older and deteriorated fruits hosting developed D. suzukii larvae was associated with the detection of a fermentation compound produced by microorganisms likely carried inside the fruit by the flies. The response of G1 females to the temporal dynamics of chemical cues emitted by the fruit–host larvae complex was consistent with the high degree of specificity of the parasitoid towards the ripening host fruits and towards D. suzukii

A multidisciplinary approach in tackling invasive species: barcoding, morphology, and metataxonomy of the leafhopper Arboridia adanae

The leafhopper genus Arboridia includes several species that feed on Vitis vinifera and cause leaf chlorosis. We report the first alien Arboridia infestation in Italy in 2021 in an Apulian vineyard. To confirm the taxonomic status of the species responsible for crop damage, and reconstruct its demographic history, we barcoded individuals from Apulia together with Arboridia spp. from Crete (Greece), A. adanae from Central Turkey and other specimens of the presumed sister species, A. dalmatina from Dalmatia (Croatia). Molecular phylogenies and barcoding gap analysis identified clades not associated with sampling locations. This result is incongruent with classical specimen assignment and is further supported by morphological analyses, which did not reveal significant differences among the populations. Therefore, we propose A. dalmatina as a junior synonym of A. adanae, which would become the only grapevine-related Arboridia species in the eastern Mediterranean. To further characterise A. adanae evolution, we performed a molecular clock analysis that suggested a radiation during the Pleistocene glaciations. Finally, to assess whether the Apulian individuals carried microorganisms of agricultural relevance, we sequenced their bacterial microbiota using 16S rRNA amplicon sequencing identifying three phytopathogens not generally associated with Arboridia activities as well as Wolbachia in one Apulian haplogroup. We discuss the agricultural implications of this infestatio

Two-Phase Stefan Problem as the Limit Case of Two-Phase Stefan Problem with Kinetic Condition

AbstractBoth one-dimensional two-phase Stefan problem with the thermodynamic equilibrium condition u(R(t),t)=0 and with the kinetic rule uε(Rε(t),t)=εRε′(t) at the moving boundary are considered. We prove, when ε approaches zero, Rε(t) converges to R(t) in C1+δ/2[0,T] for any finite T>0, 0<δ<1

How vibrational signals can guide mating behaviour in Scaphoideus titanus

The development of sustainable control methods of insects requires detailed knowledge about the biology of the pest and how it communicates with conspecifics. For example, when developing a mating disruption strategy to control vibrational communicating pest species, it is important to understand the mechanisms of its mating behaviour. We have studied the leafhopper Scaphoideus titanus, which is a vector of the severe phytoplasma grapevine disease Flavescense doreé. In laboratory experiments, males and females were positioned on different parts of the same grapevine cutting and male searching behaviour was recorded with video camera and laser vibrometry. The communication started with an identification phase in which there was an increased male pulse period and random walking after female reply. Thereafter followed a location phase, in which male calls became shorter, with more regular pulse period and correct directional decisions towards the female leaf. When a searching male reached the leaf with the female the perceived intensity of female reply increased significantly and a courtship phase was shown until copulation. With these experiments we have shown for the first time that intensity is an important parameter in vibrational communication of plant-dwelling insects. Different phases of mating behaviour are associated with different levels of perceived signal intensity and accordingly, males adjust the emission of vibrational signals and searching behaviour. Consequently, external interferences may result in loss of information necessary either for identification or location and thus preventing mating. It is possible that mating disruption with vibrations can target successfully the more susceptible behavioural phases of S. titanus

Use of substrate-borne vibrational signals to attract the Brown Marmorated Stink Bug, Halyomorpha halys

Despite the increasing number of studies on the use of acoustic stimuli to control agricultural pests, this approach is still theoretical. Many insect pests, in particular hemipterans, use vibrational signals for mating communication and therefore the application of a control strategy based on acoustic interference is a promising option. The Brown Marmorated Stink Bug, Halyomorpha halys, is causing severe economic damage on many crops in the USA and Italy. We tested a female vibrational signal, Female Signal 2 (FS2), to attract males in different settings, such as natural substrate, arenas and a cage representing an acoustic trap. We used video tracking analysis and described the vibrational amplitude field around the individuals to study the male behaviour. We found that FS2 can attract more than 50% of males to the source point and has a strong \u201cloitering\u201d effect on searching males that tend to remain in the stimulated area. We concluded that FS2 exhibits good attractiveness to H. halys males and that its potential use as a tool integrated in the currently existing pheromone traps should be tested in the field

Potential use of vibrational signals to manage the Brown Marmorated Stink Bug, Halyomorpha halys, a new invasive agricultural pest

The Brown Marmorated Stink Bug (BMSB), Halyomorpha halys (Hemiptera: Pentatomidae) is a polyphagous insect that can cause severe economic damage on different crops. In Italy this species was first recorded in the region Emilia Romagna in 2012 and in few years it spread in most of the Northern and part of the Central Italian regions. As well as in other stink bugs the mid-short range mating communication is based on the exchange of vibrational signals (duet) between sexes that is the key of pair formation, courtship and copula. During the duet females are stationary and males actively search on the plant. In other pentatomids the directionality of the searching in males, given by female attractive signals, has been demonstrated. We hypothesize that the same principle works also in BMSB and thus it would be possible to use the female calling signal to attract males towards precise source sites (i.e. artificial shakers). If confirmed, this would represent a potential implementation to the traps commonly used for BMSB monitoring, by providing an additional stimulus to enlarge the amount of captured bugs. To assess whether the female calling signal could be employed to capture males we performed different bioassays with males stimulated with either natural and synthetic vibrational signals, in different scenarios (i.e., net cages, round arenas, potted plants). Vibrational signals were recorded with laser vibrometer and a video analysis software was used to study the behavioural responses. Our experiments demonstrated the attractive effect of the female signal in all performed tests. On average, more than 50% of the tested males were attracted to vibrating sources. In addition, we also found a significant increase of walking speed, walked distance and time spent in stimulated areas. These results show promise for developing more efficient trapping techniques against H. halys in both agricultural and urban environments

Comparative life history traits of indigenous Italian parasitoids of Drosophila suzukii and their effectiveness at different temperatures

Drosophila suzukii, or spotted wing drosophila (SWD), is a highly polyphagous invasive pest which has recently invaded Europe and the Americas. Its huge economic impact is due in part to the lack of specialised natural enemies suppressing population outbreaks in newly invaded areas. By establishing new associations, endemic parasitoid species native to the invaded areas can play an important role in controlling the pest. This study aims to provide a range of baseline information on the developmental parameters and parasitisation efficacy of three Italian populations of D. suzukii parasitoids at different temperatures. The species tested were a larval parasitoid, Leptopilina heterotoma (Thomson), and two pupal parasitoids, Pachycrepoideus vindemiae (Rondani) and Trichopria drosophilae (Perkins). Two comparative experiments were set up: the first assessing longevity and the lifetime fecundity of each species at 23 °C, and the second investigating the effect of temperature on parasitisation efficacy, developmental time and sex-ratio. The results revealed different fecundity patterns for the three parasitoids, probably due to a different level of synovigeny. For T. drosophilae and P. vindemiae, the lifetime sex ratio was biased towards an increasing number of males, whereas L. heterotoma showed the opposite trend. Moreover, temperature markedly affected host-parasitoid interaction and was positively correlated with the parasitoid's developmental time, whereas the sex-ratio was not significantly influenced. On the basis of these experiments, T. drosophilae appears to be the best candidate for developing a biological control strategy.</p