Attracting Chrysopidae With Plant Volatiles for Lace Bug (Hemiptera: Tingidae) Control in Rhododendrons and Azaleas

Evaluation of olfactory and visual cues for conservation biological control of crape myrtle bark scale in urban landscapes

BACKGROUND

Acanthacoccus lagerstroemiae (crape myrtle bark scale, CMBS) is an exotic scale insect that feeds on the sap of crape myrtle trees. Heavy infestations of CMBS reduce flowering and honeydew promotes sooty mold growth on the leaves and branches, reducing the aesthetic value of crape myrtle trees in urban landscapes. Lady beetles (Coleoptera: Coccinellidae) are generalist predators that feed on CMBS. Several laboratory and field studies have demonstrated the attraction of lady beetles to olfactory and visual cues. We evaluated lady beetles' responses to olfactory lures and yellow visual attractants on infested potted and landscape trees to increase natural enemy recruitment and reduce dependence on chemical control methods.

RESULTS

Gas chromatography mass spectrometry analysis showed that limonene is the dominant volatile compound released by crape myrtles infested with CMBS. Limonene and methyl salicylate lures, alone or in combination, failed to reduce CMBS or recruit additional lady beetles to infested trees in all experiments. Yellow rectangular panels placed 1 m above the base of an infested tree recruited up to twofold more lady beetles than control trees; however, this was not statistically significant. A significant reduction in CMBS was observed on infested trees with yellow rectangular panels placed in the canopy.

CONCLUSION

Yellow rectangular panels are more likely to recruit lady beetles than limonene or methyl salicylate lures in an urban landscape. Management of CMBS is currently achieved using systemic insecticides. This study provides a basis for conservation biological control of CMBS through the recruitment of lady beetles, a significant advancement toward integrated management of this exotic pest. © 2024 Society of Chemical Industry.

Identification of a Soybean Volatile Attractive for Riptortus pedestris Using Reverse Chemical Ecology Approach

The bean bug Riptortus pedestris is a major soybean pest and a cause of the stay-green symptoms. However, the molecular mechanisms underlying its olfaction-mediated host-seeking behavior remain unclear. In this study, we compared the antennae transcriptomes of starved and nonstarved adult R. pedestris, identifying four differentially expressed odorant receptor (OR) genes. Among these, RpedOR13 showed a strong response to the host volatile 2-phenylethanol (2-PE) in Xenopus oocyte assays, while electroantennography and behavioral tests confirmed 2-PE as an effective attractant. Next, phylogenetic analysis identified RpedOR72b as a paralog of RpedOR13, with subsequent Xenopus oocyte assays confirming its specific response to 2-PE. Additionally, RNA interference experiments highlighted the crucial role of RpedOR72b in detecting 2-PE. Taken together, these findings provide new insights into the molecular mechanisms of host-seeking behavior in R. pedestris and highlight the successful application of reverse chemical ecology in OR-based screening of bioactive compounds.

Silicon supplementation can reduce infestation by azalea lace bug-(Hemiptera: Tingidae)

The azalea lace bug (ALB), Stephanitis pyrioides (Scott) (Hemiptera: Tingidae), is a pest of azaleas and rhododendrons. The application of silicon (Si) to plants has been shown to accumulate in other plants and enhance defense to other plant pests. We evaluated whether Si applications decreased ALB infestation on rhododendron leaves and increased Si accumulation in leaves. Potted plants were treated with 4 or 8 weekly applications of calcium silicate and calcium carbonate (calcium control, Ca) via foliar or soil application. In 3 out of 4 choice studies, plants treated with calcium silicate or calcium carbonate had less frass deposition and oviposition by ALB compared to controls, but treated plants did not consistently have fewer ALB adults. Leaf damage was quantified in one study and leaves with more frass as an indicator of feeding had more visible damage. In no-choice studies, there were no differences between treatments in one study, but oviposition was greater on foliar/soil Si-treated plants than controls in another study. Since rhododendron aphids (Illinoia lambersi) appeared in the greenhouse during or after studies, we compared their colonization on previously treated rhododendrons. Infestation of new leaf rosettes or random leaves by I. lambersi was lower on plants sprayed with foliar silicon or calcium applied via soil in 2 studies. Treated rhododendrons did not accumulate extra Si or Ca in leaves compared to controls. In general, silicon or calcium application protected rhododendrons from ALB oviposition and aphid colonization in free-choice conditions, and may be part of an integrated pest management program.

Comparative Metabolomic Responses of Three Rhododendron Cultivars to the Azalea Lace Bug (Stephanitis pyrioides)

Rhododendron, with its high ornamental value and ecological benefits, is severely impacted by the azalea lace bug (Stephanitis pyrioides), one of its primary pests. This study utilized three Rhododendron cultivars, 'Zihe', 'Yanzhimi', and 'Taile', to conduct a non-targeted metabolomic analysis of leaf samples before and after azalea lace bug stress using headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME/GCMS) and liquid chromatography-mass spectrometry (LCMS). A total of 81 volatile metabolites across 11 categories and 448 nonvolatile metabolites across 55 categories were detected. Significant differences in metabolic profiles were observed among the different cultivars after pest stress. A total of 47 volatile compounds and 49 nonvolatile metabolites were upregulated in the most susceptible cultivar 'Zihe', including terpenes, alcohols, nucleotides, amino acids, and carbohydrates, which are involved in energy production and secondary metabolism. Conversely, 'Yanzhimi' showed a downtrend in both the differential volatiles and metabolites related to purine metabolism and zeatin biosynthesis under pest stress. The resistant cultivar 'Taile' exhibited moderate changes, with 17 volatile compounds and 17 nonvolatile compounds being upregulated and enriched in the biosynthesis of amino acids, pentose, glucuronate interconversions, carbon metabolism, etc. The phenylalanine metabolic pathway played an important role in the pest resistance of different susceptible cultivars, and relevant metabolites such as phenylethyl alcohol, methyl salicylate, and apigenin may be involved in the plant's resistance response. The results of this study provide a new perspective on the metabolomics of Rhododendron-insect interactions and offer references for the development of pest control strategies.

Coacervate-Enhanced Deposition of Sprayed Pesticide on Hydrophobic/Superhydrophobic Abaxial Leaf Surfaces

Deposition of high-speed droplets on inverted surfaces is important to many fundamental scientific principles and technological applications. For example, in pesticide spraying to target pests and diseases emerging on abaxial side of leaves, the downward rebound and gravity of the droplets make the deposition exceedingly difficult on hydrophobic/superhydrophobic leaf underside, causing serious pesticide waste and environmental pollution. Here, a series of bile salt/cationic surfactant coacervates are developed to attain efficient deposition on the inverted surfaces of diverse hydrophobic/superhydrophobic characteristics. The coacervates have abundant nanoscale hydrophilic/hydrophobic domains and intrinsic network-like microstructures, which endow them with efficient encapsulation of various solutes and strong adhesion to surface micro/nanostructures. Thus, the coacervates with low viscosity achieve high-efficient deposition on superhydrophobic abaxial-side of tomato leaves and inverted artificial surfaces with a water contact angle from 170° to 124°, much better than that of commercial agricultural adjuvants. Intriguingly, the compactness of network-like structures dominantly controls adhesion force and deposition efficiency, and the most crowded one leads to the most efficient deposition. The tunable coacervates can help comprehensively understand the complex dynamic deposition, and provide innovative carriers for depositing sprayed pesticides on abaxial and adaxial sides of leaves, thereby potentially reducing pesticide use and promoting sustainable agriculture.

Aphid-repellent, ladybug-attraction activities, and binding mechanism of methyl salicylate derivatives containing geraniol moiety

BACKGROUND

Aphids have been mainly controlled by traditional chemical insecticides, resulting in unamiable risk to the environment over the last decades. Push-pull strategy is regarded as a promising eco-friendly approach for aphid management through repelling aphid away and attracting their natural enemy. Methyl salicylate (MeSA), one of typical HIPVs (herbivore-induced plant volatiles), can repel aphids and attract ladybugs. Our previous studies discovered a new lead compound 3e, a salicylate-substituted carboxyl (E)-β-farnesene derivative that had effective aphid-repellent activity. However, whether 3e has attractive activity to ladybug like MeSA is unknown. Meanwhile, to discover a new derivative for both deterring aphid and recruiting ladybug is meaningful for green control of aphids.

RESULTS

Through the structural optimization of 3e, 14 new derivatives were designed and synthesized. Among them, compounds 4e and 4i had good aphid (Acyrthosiphon pisum) repellent activity, and compounds 3e, 4e and 4i had significant ladybug (Harmonia axyridis) attractive activity to males. Particularly, 4i exhibited manifest attractive effect on the females as well. Binding mechanism showed that 4i not only bound effectively with the aphid (Acyrthosiphon pisum) target ApisOBP9 thanks to its multiple hydrophobic interactions and hydrogen-bond, but also had strong binding affinity with ladybug target HaxyOBP15 due to the suitable steric space. Additionally, 4i displayed low toxicity to bee Apis mellifera.

CONCLUSION

Compound 3e does exhibit attractive activity to male ladybug as MeSA. However, the new derivative 4i, with both pleasant aphid-repellent and ladybug-attraction activities, can be considered as a novel potential push-pull candidate for aphid control in sustainable agriculture. © 2022 Society of Chemical Industry.

Methyl Salicylate Can Benefit Ornamental Pest Control, and Does Not Alter Per Capita Predator Consumption at Close-Range

Methyl salicylate (MeSA) is an herbivore-induced plant volatile widely tested for attracting natural enemies for pest control. MeSA is commercially sold as slow-release lures or as a spray. While MeSA application has increased the abundance of natural enemies in numerous food crops, its ability to reduce pests for crop protection is not as frequently demonstrated. Our first objective was to test MeSA lures in ornamental fields where few studies have been done, and monitor natural enemies, pests, and crop protection. A 2-year study in spruce container yards revealed more aphid parasitoids (Pseudopraon sp.), fewer aphids (Mindarus obliquus) on shoot tips, and less shoot tip damage in MeSA plots during the first year. A 2-year study in red maple fields revealed more predatory lady beetles and rove beetles, and parasitic Ceraphronidae, Diapriidae, and Chalcidoidea in one or both years with MeSA. Fewer pest thrips were also captured in MeSA plots, though it is not clear whether this was due to enhanced predation or reduced colonization. Maple growth as measured by stem diameter change did not differ with MeSA use. A 2-year study examining predation on sentinel Halyomorpha halys eggs in various mature ornamental stock blocks found no increase in predation except for 1 month, though green lacewings, lady beetles, and predatory thrips occurred more in MeSA plots in the first year. While MeSA is expected to enhance biological control by herding in natural enemies, the impacts that applied volatiles have on predator efficiency is mostly unknown. Thus, our second objective examined how volatiles would impact feeding rates at close-range. Adult carabid Pterostichus melanarius, adult coccinellids Coccinella septempunctata and Harmonia axyridis, and larval lacewing Chrysoperla rufilabris consumed their prey at similar rates in the presence/absence of MeSA when food was presented directly in a 28 cm2 or 30 ml arena, or when foraging in a 520 cm2 outdoor soil arena or 946 ml arena with aphids on leaves.

Identification and expression profile of odorant-binding proteins in the parasitic wasp Microplitis pallidipes using PacBio long-read sequencing

Microplitis pallidipes Szépligeti (Hymenoptera: Braconidae) is an important parasitic wasp of second and third-instar noctuid larvae such as the insect pests Spodoptera exigua, Spodoptera litura, and Spodoptera frugiperda. As in other insects, M. pallidipes has a chemosensory recognition system that is critical to foraging, mating, oviposition, and other behaviors. Odorant-binding proteins (OBPs) are important to the system, but those of M. pallidipes have not been determined. This study used PacBio long-read sequencing to identify 170,980 M. pallidipes unigenes and predicted 129,381 proteins. Following retrieval of possible OBP sequences, we removed those that were redundant or non-full-length and eventually cloned five OBP sequences: MpOBP2, MpOBP3, MpOBP8, MpOBP10, and MpPBP 429, 429, 459, 420, and 429 bp in size, respectively. Each M. pallidipes OBP had six conserved cysteine residues. Phylogenetic analysis revealed that the five OBPs were located at different branches of the phylogenetic tree. Additionally, tissue expression profiles indicated that MpOBP2 and MpPBP were mainly expressed in the antennae of male wasps, while MpOBP3, MpOBP8, and MpOBP10 were mainly expressed in the antennae of female wasps. MpOBP3 was also highly expressed in the legs of female wasps. Temporal profiles revealed that the expression of each M. pallidipes OBP peaked at different days after emergence to adulthood. In conclusion, we identified five novel odorant-binding proteins of M. pallidipes and demonstrated biologically relevant differences in expression patterns.

Identification of Blackberry (Rubus fruticosus) Volatiles as Drosophila suzukii Attractants

The spotted wing drosophila, Drosophila suzukii, is an invasive pest species from Southeast Asia that was recently introduced in Europe and North America. As this fruit fly lays its eggs in ripening soft-skinned fruit, it causes great damage to a variety of crops, including cherries, blueberries, blackberries, raspberries, grapes, plums and strawberries. Consequently, there is a great demand for an effective and species-specific lure, which requires the development of successful attractants. Until now, there is no lure available that is species-specific and can detect the presence of D. suzukii before infestation. As blackberry (Rubus fruticosus) is one of the preferred host crops of D. suzukii, the volatile compounds of R. fruticosus berries are here identified and quantified using multiple headspace SPME (solid phase micro extraction) GC-MS (gas chromatography-mass spectrometry). Subsequently, the attractivity of 33 of the identified compounds was tested with a two-choice laboratory bioassay. Acetaldehyde, hexyl acetate, linalool, myrtenol, L-limonene and camphene came out as significantly attractive to D. suzukii. The first four attractive compounds induced the strongest effect and therefore provided the best prospects to be implemented in a potential lure. These findings could contribute towards the development of more effective attractants for monitoring and mass trapping D. suzukii.

Methyl Salicylate Fails to Enhance Arthropod Predator Abundance or Predator to Pest Ratios in Cotton

Conservation biological control is a fundamental tactic in integrated pest management (IPM). Greater biological control services can be achieved by enhancing agroecosystems to be more favorable to the presence, survival, and growth of natural enemy populations. One approach that has been tested in numerous agricultural systems is the deployment of synthetic chemicals that mimic those produced by the plant when under attack by pests. These signals may attract arthropod natural enemies to crop habitats and thus potentially improve biological control activity locally. A 2-yr field study was conducted in the cotton agroecosystem to evaluate the potential of synthetic methyl salicylate (MeSA) to attract native arthropod natural enemies and to enhance biological control services on two key pests. Slow-release packets of MeSA were deployed in replicated cotton plots season long. The abundance of multiple taxa of natural enemies and two major pests were monitored weekly by several sampling methods. The deployment of MeSA failed to increase natural enemy abundance and pest densities did not decline. Predator to prey ratios, used as a proxy to estimate biological control function, also largely failed to increase with MeSA deployment. One exception was a season-long increase in the ratio of Orius tristicolor (White) (Hemiptera: Anthocoridae) to Bemisia argentifolii Bellows and Perring (= Bemisia tabaci MEAM1) (Hemiptera: Aleyrodidae) adults within the context of biological control informed action thresholds. Overall results suggest that MeSA would not likely enhance conservation biological control by the natural enemy community typical of U.S. western cotton production systems.