Attraction of the Air Potato Leaf Beetle, Lilioceris Cheni, (Coleoptera: Chrysomelidae) to leaf Volatiles of the Air Potato, Dioscorea bulbifera.

Air potato, Dioscorea bulbifera L., is an invasive vine found in the southeastern United States and is native to Asia and Africa. The air potato leaf beetle Lilioceris cheni (Coleoptera: Chrysomelidae), is a host specific biological control agent introduced for D. bulbifera control. In this study, odor cues that control the attraction of L. cheni to D. bulbifera were investigated. The first experiment investigated the response of L. cheni to D. bulbifera leaves versus no leaves in the presence or absence of air flow. The experiment showed a significant response of L. cheni to D. bulbifera leaves in the presence of air flow with leaves placed upwind. When air flow and/or leaves were absent, L. cheni dispersed randomly between the upwind and downwind targets, indicating L. cheni uses volatiles from D. bulbifera in host selection. The second experiment investigated L. cheni response to undamaged, larval-damaged, and adult-damaged plants. Lilioceris cheni showed preference to move towards conspecific damaged plants compared to undamaged plants but did not discriminate between larvae-damaged or adult-damaged plants. The third experiment investigated volatile profiles of damaged D. bulbifera plants using gas chromatography coupled with mass spectroscopy. We found significant differences in volatile profiles between adult and larval damaged plants compared to mechanically damaged and undamaged plants, with increases in 11 volatile compounds. However, larval and adult-damaged volatile profiles did not differ. The information acquired during this study could be used to develop strategies to monitor for L. cheni and improve its biological control program.

Deciphering Plant-Insect-Microorganism Signals for Sustainable Crop Production.

Agricultural crop productivity relies on the application of chemical pesticides to reduce pest and pathogen damage. However, chemical pesticides also pose a range of ecological, environmental and economic penalties. This includes the development of pesticide resistance by insect pests and pathogens, rendering pesticides less effective. Alternative sustainable crop protection tools should therefore be considered. Semiochemicals are signalling molecules produced by organisms, including plants, microbes, and animals, which cause behavioural or developmental changes in receiving organisms. Manipulating semiochemicals could provide a more sustainable approach to the management of insect pests and pathogens across crops. Here, we review the role of semiochemicals in the interaction between plants, insects and microbes, including examples of how they have been applied to agricultural systems. We highlight future research priorities to be considered for semiochemicals to be credible alternatives to the application of chemical pesticides.

Deadly scents: Exposure to plant volatiles increases mortality of entomopathogenic nematodes during infection.

Plants attacked by insects commonly mobilize various defense mechanisms, including the biosynthesis and release of so-called herbivore-induced plant volatiles (HIPVs). Entomopathogenic nematodes (EPNs) can be attracted to these belowground HIPVs, which can enhance biocontrol services from EPNs. However, recent research has also demonstrated that HIPVs can induce and initiate insect immune responses, decreasing the insect's susceptibility to pathogens and parasites. Therefore, experiments were conducted to test the impact of HIPVs on insects and EPNs during the initial stage of EPN infection. Compounds that can impact EPN attraction and infectivity such as pregeijerene, ß-caryophyllene, and α-pinene, and compounds that have been determined to increase or decrease susceptibility of insects to pathogens, such as (Z)-3-hexenyl acetate, linalool, and ß-ocimene, were selected. Exposure of Galleria mellonella larvae to pregeijerene, linalool, ß-ocimene and α-pinene during invasion significantly increased mortality of Steinernema diaprepesi and Heterorhabditis bacteriophora after 48 h. Larval treatment with ß-caryophyllene only increased mortality for Heterorhabditis bacteriophora. (Z)-3-hexenyl acetate did not cause differential mortality from the controls for either nematode species. In additional experiments, we found that EPNs exposed to α-pinene and linalool were more readily recognized by the insects' immune cells compared to the control treatment, thus the observed increased mortality was likely due to HIPVs-EPN interactions with the insect's immune system. These results show that the presence of HIPVs can impact EPN survival in the model host, G. mellonella.

Using Chemical Ecology to Enhance Weed Biological Control.

In agricultural systems, chemical ecology and the use of semiochemicals have become critical components of integrated pest management. The categories of semiochemicals that have been used include sex pheromones, aggregation pheromones, and plant volatile compounds used as attractants as well as repellents. In contrast, semiochemicals are rarely utilized for management of insects used in weed biological control. Here, we advocate for the benefit of chemical ecology principles in the implementation of weed biocontrol by describing successful utilization of semiochemicals for release, monitoring and manipulation of weed biocontrol agent populations. The potential for more widespread adoption and successful implementation of semiochemicals justifies multidisciplinary collaborations and increased research on how semiochemicals and chemical ecology can enhance weed biocontrol programs.

Desorption Temperature, Solid-Phase Microextraction (SPME), and Natural Product Analyses, how Low Can we Go?

Solid phase microextraction (SPME) has become a common technique for volatile sampling due to its ease of use and limited technical requirements. The solvent-free nature of SPME is also exceptionally attractive for gas chromatography mass spectrometry (GC/MS) analysis. To ensure efficient transfer of the sample to the GC, the manufacturer recommend injector desorption temperatures in the range of 200 to 320 °C. A high desorption temperature can, however, have unwanted effects on analyses of plant and insect produced semiochemicals. By investigating the quantitative and qualitative chromatographic responses at varying inlet temperatures for a component blend of seven plant produced volatile compounds, we found the thermally labile plant-nematode signaling compound, pregeijerene to degrade to geijerene at all tested temperatures within the recommended range (200, 240, and 280 °C), but that it did not break down with an inlet temperature below 200 °C (100 °C and 150 °C). Degradation was also detected for the sesquiterpene germacrene D, but only at the highest inlet temperature tested (280 °C). Surprisingly, an inlet temperature of 200 °C gave the highest sample recovery, measured as total peak area while an inlet temperature of 100 °C as well as 280 °C gave the lowest total area values. An increase in desorption time from 3 to 5 min. Resulted in a recovery at 100 °C close to that obtained at 200 °C. Peak broadening was minimal, and only observed at the 100 °C inlet temperature. Based on these results, we highly recommend that SPME users include desorption temperature as one variable when developing sampling procedures for novel biological systems to ensure that potentially present thermally labile compounds are not degraded.

An Herbivore-Induced Plant Volatile From Saltcedar (Tamarix spp.) Is Repellent to Diorhabda carinulata (Coleoptera: Chrysomelidae).

The leaf beetle Diorhabda carinulata Desbrochers (Coleoptera: Chrysomelidae) was introduced into the United States in 1999 for classical biological control of the exotic woody invader saltcedar (Tamarix spp. L. [Caryophyllales: Tamaricaceae]). The recent southern expansion of the range of D. carinulata in the United States has precipitated conflict between proponents of biological control of Tamarix and those with concerns over habitat conservation for avian species. Several semiochemicals that mediate aggregations by this species have been reported, but no repellent compounds have been recorded thus far. We now report a repellent compound, 4-oxo-(E)-2-hexenal, induced by adult D. carinulata feeding on saltcedar foliage. Collection of headspace volatiles, gas chromatography mass spectrometry, and electroantennographic analyses identified 4-oxo-(E)-2-hexenal as an insect-induced compound that is antennally active. Behavioral and exposure assays were conducted to test for repellency and toxicity in adults and larvae. Headspace volatiles were also collected from adult males exposed to 4-oxo-(E)-2-hexenal to determine the impact exposure might have on the emission of the aggregation pheromone. 4-Oxo-(E)-2-hexenal elicited electrophysiological responses in adults of both sexes. Behavioral responses indicated repellency across multiple doses for reproductive D. carinulata adults but not in nonreproductive adults. Exposure assays indicated altered behaviors in first instar larvae and adults, but not in third instar larvae. Collection of headspace volatiles indicated that exposure to 4-oxo-(E)-2-hexenal did not alter emission of the D. carinulata aggregation pheromone by adult males. The continued development and field deployment of this repellent compound may provide a new tool for the management of D. carinulata.

Establishing Diorhabda carinulata: Impact of Release Disturbances on Pheromone Emission and Influence of Pheromone Lures on Establishment.

Before weed biocontrol insects are transported and released in a new area, they are commonly collected into small paper containers, chilled, and kept under dark conditions. This process can be termed a pre-release protocol. The influence of a pre-release protocol on establishment success of a gregarious biological control agent was assessed using the northern tamarisk beetle, Diorhabda carinulata (Desbrochers), and its exotic, invasive host plant saltcedar (Tamarix spp.). Pre-release protocol impacts on aggregation pheromone production by D. carinulata were characterized under controlled conditions. Additional experiments were undertaken to determine if deployment of aggregation pheromone lures might enhance the agent's persistence at release sites. Adults that experienced the pre-release protocol produced less aggregation pheromone compared to undisturbed adults. Olfactometer bioassays indicated that a cohort of adults subjected to the pre-release protocol were less attractive to other adults than a control cohort. Efficacy of aggregation pheromone-based lures to retain adults at release sites was evaluated by comparing capture numbers of adult beetles at paired treatment and control release sites, 10-14 days after the release of 300, 500, or 1000 individuals. A greater number of adult D. carinulata were captured where the pheromone lures had been deployed compared to control release sites. Application of aggregation pheromone when a new release of D. carinulata is planned should allow biological control practitioners to increase retention of beetles at a release site.

Field demonstration of a semiochemical treatment that enhances Diorhabda carinulata biological control of Tamarix spp.

The northern tamarisk beetle Diorhabda carinulata (Desbrochers) was approved for release in the United States for classical biological control of a complex of invasive saltcedar species and their hybrids (Tamarix spp.). An aggregation pheromone used by D. carinulata to locate conspecifics is fundamental to colonization and reproductive success. A specialized matrix formulated for controlled release of this aggregation pheromone was developed as a lure to manipulate adult densities in the field. One application of the lure at onset of adult emergence for each generation provided long term attraction and retention of D. carinulata adults on treated Tamarix spp. plants. Treated plants exhibited greater levels of defoliation, dieback and canopy reduction. Application of a single, well-timed aggregation pheromone treatment per generation increased the efficacy of this classical weed biological control agent.

Semiochemicals to enhance herbivory by Diorhabda carinulata aggregations in saltcedar (Tamarix spp.) infestations.

BACKGROUND: Semiochemicals for monitoring, attracting or repelling pest and beneficial organisms are increasingly deployed in agricultural and forest systems for pest management. However, the use of aggregation pheromones and host-plant attractants for the express purpose of increasing the efficacy of classical biological control agents of weeds has not been widely reported. Therefore, we conducted field-based assays to determine if a specialized wax-based matrix impregnated with an aggregation pheromone of the northern tamarisk beetle Diorhabda carinulata (Desbrochers) or host-plant volatiles could increase the efficacy of D. carinulata. RESULTS: The aggregation pheromone and host-plant volatiles were formulated for field application using a wax-based matrix. Reported release rates suggest that this matrix is a viable formulation for enhancing D. carinulata aggregations under field conditions. Pheromone-treated saltcedar plants (Tamarix spp.) not only had higher densities of adult and larval D. carinulata, but also sustained greater levels of foliar damage than control plants. Increased damage from the focused feeding of D. carinulata caused an increase in foliar dieback and decrease in live canopy volume of semiochemical-treated plants. CONCLUSION: Field deployment of these semiochemical formulations could be useful in directing populations of D. carinulata for increased impact on Tamarix spp. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.