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 mass-trapped 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 conditions.

Comparing the effectiveness of different insecticide application orders for suppressing Drosophila suzukii Matsumura (Diptera: Drosophilidae) infestation: experimental and modeling approaches.

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is a key pest of soft-skinned fruit such as blackberry and blueberry. Differing seasonal spray regimes are expected to have variable effects on D. suzukii populations. Semi-field cage trials were performed at three locations in the United States (Georgia, Oregon, and North Carolina) on blueberry and blackberry crops to evaluate this hypothesis. Insecticides with different efficacy rates (ZC - zeta-cypermethrin, SPI - spinetoram, CYAN - cyantraniliprole) were applied during field experiments conducted within large cages. Treatment schedules consisted of two insecticide applications which performed over three weeks. Seasonal treatment schedules were applied in the following order: ZC-CYAN and CYAN-ZC in rabbiteye and highbush blueberry with the addition of a ZC-SPI treatment applied in blackberry. In addition, a population model was applied to simulate the relative efficacy of the insecticide schedules in Oregon on D. suzukii population model based on previously published efficacy, biological, and weather parameters. Overall, all schedules resulted in reduced D. suzukii infestation compared to untreated control (UTC) treatments, with statistical differences in all three locations. The numerically lower infestation was found in some cases in ZC-CYAN schedule. Population modeling conducted exclusively for blueberry, and the simulations indicated no discernible differences between the two respective schedules (ZC-CYAN vs CYAN-ZC). The present study demonstrates that seasonal infestation of D. suzukii could be suppressed irrespective of application order. Additional research is required to assess the optimal timing and sequence of insecticide applications for controlling seasonal populations of D. suzukii in fruit crops. Such information could be invaluable for growers who are seeking to strategize their insecticide applications.

A Horticultural Cuticle Supplement Can Impact Quality Characters and Drosophila suzukii Damage of Several Small and Stone Fruit.

Surface wax and other cellular building blocks play an important role in preserving fruit integrity from biotic and abiotic adversities. Huge energy expenses are made by plants to place these protective compounds onto the epidermal cuticle. Sprayable plant and fruit coatings have been developed to protect plant tissues from environmental stresses, pathogens, and arthropods. The aim of this study was to determine if an experimental cuticle supplement containing waxes can affect fruit quality parameters such as firmness and size of various crops. Cherry, blueberry, and winegrape plants treated with the cuticle supplement showed significant increases in berry firmness ranging from 4.6 to 11.6%. No quality benefits were however observed on blackberry. Cuticle supplement applications did not significantly affect berry size. Laboratory trials resulted in a 54% mean reduction in a model pest insect i.e., Drosophila suzukii egg laying on blueberry. Short-duration field trials over 72 ±â€…2 to 96 ±â€…2 h on commercial-standard blueberry bushes resulted in 50-93.4% reductions of D. suzukii damage. Longer-term field trials on cherry and blueberry challenged with egg-laying D. suzukii showed reductions of damage ranging from 45 to 95%, up to 30 d after initial cuticle supplement applications. These results indicate that the cuticle supplement significantly alters berry firmness and reduces D. suzukii damage under commercial production conditions. One factor that may contribute to this reduction includes improved fruit quality parameters. The current work serves to expand integrated pest management options to control D. suzukii populations in commercial field settings.

Methods for Rearing the Parasitoid Ganaspis brasiliensis, a Promising Biological Control Agent for the Invasive Drosophila suzukii.

Native to East Asia, the spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), has established widely in the Americas, Europe, and parts of Africa over the last decade, becoming a devastating pest of various soft-skinned fruits in its invaded regions. Biological control, especially by means of self-perpetuating and specialized parasitoids, is expected to be a viable option for sustainable area-wide management of this highly mobile and polyphagous pest. Ganaspis brasiliensis Ihering (Hymenoptera: Figitidae) is a larval parasitoid that is widely distributed in East Asia, and has been found to be one of the most effective parasitoids of D. suzukii. Following rigorous pre-introduction evaluations of its efficacy and potential non-target risks, one of the more host-specific genetic groups of this species (G1 G. brasiliensis) has been approved recently for introduction and field release in the United States and Italy. Another genetic group (G3 G. brasiliensis), which was also commonly found to attack D. suzukii in East Asia, may be considered for introduction in the near future. There is currently enormous interest in rearing G. brasiliensis for research or in mass-production for field release against D. suzukii. This protocol and associated video article describe effective rearing methods for this parasitoid, both on a small scale for research and a large scale for mass-production and field release. These methods may benefit further long-term research and use of this Asian-native parasitoid as a promising biological control agent for this global invasive pest.

Drosophila suzukii (Diptera: Drosophilidae): A Decade of Research Towards a Sustainable Integrated Pest Management Program.

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) also known as spotted-wing drosophila (SWD), is a pest native to Southeast Asia. In the last few decades, the pest has expanded its range to affect all major European and American fruit production regions. SWD is a highly adaptive insect that is able to disperse, survive, and flourish under a range of environmental conditions. Infestation by SWD generates both direct and indirect economic impacts through yield losses, shorter shelf life of infested fruit, and increased production costs. Fresh markets, frozen berries, and fruit export programs have been impacted by the pest due to zero tolerance for fruit infestation. As SWD control programs rely heavily on insecticides, exceedance of maximum residue levels (MRLs) has also resulted in crop rejections. The economic impact of SWD has been particularly severe for organic operations, mainly due to the limited availability of effective insecticides. Integrated pest management (IPM) of SWD could significantly reduce chemical inputs but would require substantial changes to horticultural management practices. This review evaluates the most promising methods studied as part of an IPM strategy against SWD across the world. For each of the considered techniques, the effectiveness, impact, sustainability, and stage of development are discussed.

Fine Morphology of Antennal and Ovipositor Sensory Structures of the Gall Chestnut Wasp, Dryocosmus kuriphilus.

Dryocosmus kuriphilus is a gall-inducing insect, which can cause significant damage on plants of the genus Castanea Mill., 1754. Antennae and ovipositor are the main sensory organs involved in the location of suitable oviposition sites. Antennal sensilla are involved in the host plant location, while ovipositor sensilla assess the suitability of the ovipositional bud. On both organs, diverse sensillar organs are present. Here, the distribution and ultrastructural organization of the sensilla were investigated by scanning and transmission electron microscopy. The antennae of D. kuriphilus are filiform and composed of 14 antennomeres, with the distal flagellomere bearing the highest number of sensilla. On the antennae, 6 sensilla types were found; sensilla chaetica, campaniformia, coeloconica-I, coeloconica-II, trichoidea and placoidea. The sensilla placoidea and trichoidea were the most abundant types. On the external walls of the ovipositor, gustatory and mechanoreceptive sensilla were observed. Internally, the egg channel hosted two additional sensory structures. The putative functional role of each sensilla in the context of insect's ecology is discussed as well as the ovipositional mechanism used by this insect.

Structural and transcriptional evidence of mechanotransduction in the Drosophila suzukii ovipositor.

Drosophila suzukii is an invasive pest that prefers to lay eggs in ripening fruits, whereas most closely related Drosophila species exclusively use rotten fruit as oviposition site. This behaviour is allowed by an enlarged and serrated ovipositor that can pierce intact fruit skin, and by multiple contact sensory systems (mechanosensation and taste) that detect the optimal egg-laying substrates. Here, we tested the hypothesis that bristles present in the D. suzukii ovipositor tip contribute to these sensory modalities. Analysis of the bristle ultrastructure revealed that four different types of cuticular elements (conical pegs type 1 and 2, chaetic and trichoid sensilla) are present on the tip of each ovipositor plate. All of them have a poreless shaft and are innervated at their base by a single neuron that ends in a distal tubular body, thus resembling mechanosensitive structures. Fluorescent labelling in D. suzukii and D. melanogaster revealed that pegs located on the ventral side of the ovipositor tip are innervated by a single neuron in both species. RNA-sequencing profiled gene expression, notably sensory receptor genes of the terminalia of D. suzukii and of three other Drosophila species with changes in their ovipositor structure (from serrated to blunt ovipositor: Drosophila subpulchrella, Drosophila biarmipes and D. melanogaster). Our results revealed few species-specific transcripts and an overlapping expression of candidate mechanosensitive genes as well as the presence of some chemoreceptor transcripts. These experimental evidences suggest a mechanosensitive function for the D. suzukii ovipositor, which might be crucial across Drosophila species independently from ovipositor shape.

The process of pair formation mediated by substrate-borne vibrations in a small insect.

The ability to identify and locate conspecifics depends on reliable transfer of information between emitter and receiver. For a majority of plant-dwelling insects communicating with substrate-borne vibrations, localization of a potential partner may be a difficult task due to their small body size and complex transmission properties of plants. In the present study, we used the leafhopper Scaphoideus titanus as a model to investigate duetting and mate searching associated with pair formation. Studying these insects on a natural substrate, we showed that the spatio-temporal structure of a vibrational duet and the perceived intensity of partner's signals influence the mating behaviour. Identification, localization and courtship stages were each characterized by a specific duet structure. In particular, the duet structure differed in synchronization between male and female pulses, which enables identification of the partner, while the switch between behavioural stages was associated with the male-perceived intensity of vibrational signals. This suggests that males obtain the information about their distance from the female and optimize their strategy accordingly. More broadly, our results show that even in insects smaller than 1cm, vibrational signals provide reliable information needed to find a mating partner.

Comparative neuroanatomy of the antennal lobes of 2 homopteran species.

We compared the morphology of the primary olfactory center, the antennal lobe (AL), in 2 homopteran insects, Hyalesthes obsoletus Signoret (Homoptera: Cixiidae) and Scaphoideus titanus Ball (Homoptera: Cicadomorpha). The comparison between the ALs of the 2 species is particularly interesting considering that, although both use volatile cues to locate their host plants, their feeding behavior differs considerably: specifically, H. obsoletus is a highly polyphagous species, whereas S. titanus is strictly monophagous (on grapevine). Our investigation of the AL structure using immunocytochemical staining and antennal backfills did not reveal any sexual dimorphism in either the size of the ALs or in the size of individual glomeruli for either species. Instead, the AL of H. obsoletus displayed numerous and well-delineated glomeruli (about 130 in both sexes) arranged in a multilayered structure, whereas the smaller AL of S. titanus contained fewer than 15 glomerular-like structures. This difference is likely to reflect the comparatively reduced olfactory abilities in S. titanus, probably as a consequence of the reduced number of volatiles coming from the single host plant. Instead, in H. obsoletus, the ability to distinguish among several host plants may require a more complex olfactory neuronal network.

The Johnston's organ of three homopteran species: a comparative ultrastructural study.

A transmission electron-microscopy study has been carried out on the pedicel of three homopteran species, with particular focus on the leafhopper Scaphoideus titanus Ball. The two other species, the planthoppers Hyalesthes obsoletus Signoret and Metcalfa pruinosa Say, were investigated in order to compare the ultrastructure of the Johnston's organ (JO) among representatives of the Auchenorrhyncha group. The results showed the presence of a well developed JO located within the pedicel. Depending on the species the JO is made of 25 up to 72 scolopidia arranged in a coronal array. Each scolopidium is connective, heterodynal, amphinematic and hosts three structurally dissimilar sensory neurons. Two of them have a type 1 ciliary segment while the third bears a type 2 cilium. The type 2 dendrite tip is associated with a tubular cap and is longer than the others, ending into the cuticle at the base of the flagellum. Other scolopidia with one or two neurons were found in S. titanus, forming an accessory organ. The presence of such a well developed mechanosensory apparatus is discussed in relation with the lifestyle of the three species.

Fine structure of the antennal glands of the ant nest beetle Paussus favieri (Coleoptera, Carabidae, Paussini).

The antennae of the ant nest beetle Paussus favieri are studied by using both SEM and TEM. In the myrmecophilous genus Paussus, these structures are composed of three joints: scape, pedicel and a wide third joint, the "antennal club", resulting from the fusion of antennomeres A3-A11 (flagellum). The antennal club shows an exceptional glandular activity, with the presence of pores mostly crowded in special hairless cuticular areas, surrounding the base of single setae, grouped at the base of tufts of setae, or positioned inside deep pockets that store the secretions, with filiform material arising from them. The surface of A1 and A3 are covered by mechanoreceptors, modified to spread the glandular exudates, while the chemoreceptors are restricted to the apex of the club. The fine structural analysis shows a great number of antennal glands, that can be referred to three main typologies: type A (GhA) bi-cellular, composed of a large secretory cell and a small duct cell, positioned close to the antennal surface; type B (GhB), tri-cellular, composed of two secretory cells and one duct cell, less frequent and positioned deep inside the antennal club; type C (GhC), rare, located deeply within the antennal lumen, in the vicinity of the trophocytes. This complexity indicates that more than one substance could be released from the antennae. Possible functional aspects of the secretions dealing with symbiotic interaction with the host ants are discussed.