State-Dependent Plasticity in Response to Host-Plant Volatiles in a Long-Lived Moth, Caloptilia fraxinella (Lepidoptera: Gracillariidae)

Volatile cues of enhanced attractiveness to Parapanteles hyposidrae (Wilkinson) wasps mediated by jasmonic and salicylic acid pathways synergism in tea plant

BACKGROUND

The jasmonic acid (JA) and salicylic acid (SA) pathways are often thought to interact antagonistically in plants when mediating anti-herbivore resistance. However, we previously found that the two pathways in tea plant interact synergistically when treated with 1.5 mmol/L methyl jasmonate (MeJA) and 20 mmol/L SA at 12 h intervals (MeJA+SA treatment). Here, we investigated how and why JA-SA synergism in tea plants affected chemotaxis of Parapanteles hyposidrae (Wilkinson) wasps, the parasite of tea geometers.

RESULTS

Wasp attractiveness of MeJA+SA-treated plants was 1.3-fold higher than MeJA-treated plants, although SA-treated plants could not attract more wasps. Five attractive compounds, including (Z)-3-hexenyl acetate, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), indole and (E,E)-α-farnesene, were emitted more by MeJA+SA-treated than MeJA-treated plants. Based on the difference in volatiles induced by MeJA and MeJA+SA treatments, five attractive components were separately added to artificial MeJA-induced volatiles (MV) or taken out from artificial MeJA+SA-induced volatiles (MSV). The attractiveness of MV to wasps was enhanced when DMNT or indole was added, whereas the attractiveness of MSV decreased when DMNT, indole or linalool was taken out. When DMNT and indole were both added into MV, the attractiveness of volatile blend to wasps became similar to MSV.

CONCLUSION

Increased DMNT and indole emissions are the key cues causing volatiles mediated by JA-SA synergism to be more attractive to P. hyposidrae wasps than those mediated by JA pathway alone. This provides new insights into the phytohormone pathway networks in tea plants and the development of natural enemy attractants. © 2025 Society of Chemical Industry.

Energy Use During Flight Impacts Semiochemical Response in the Mountain Pine Beetle

Global climate change drives the range expansion of various taxa, including the mountain pine beetle (Dendroctonus ponderosae; MPB). Dispersal and host colonization dictate spread and establishment of MPB populations, but this comes with energetic, time, risk, and opportunity costs. As MPB exhibit continuous flight polyphenisms, researchers have proposed that energy use during flight may trigger responsiveness to the semiochemicals that orchestrate the colonization of host pine trees, but this effect has not been demonstrated empirically. Here, we test the hypothesis that flight exercise impacts subsequent behavioral response to semiochemicals in two olfactometer experiments that simulate 1) female beetle pioneer response to host volatiles and 2) male and female joining beetle response to host volatiles and the female-produced aggregation pheromone, trans-verbenol. We also assess antennal response of female beetles to α-pinene post-flight in an electroantennogram bioassay. Female MPB with low condition due to energy expenditure responded strongly to host semiochemicals post-flight. The antennal response of female MPB to the host volatile α-pinene increased with relative lipid content of beetles. Male behavioral response to semiochemicals was not influenced by body condition or exercise by flight. The effect of flight and body condition on orientation to semiochemical cues may influence individual dispersal patterns. These findings should be considered in the refinement of dispersal models that incorporate individual variability to predict spread of MPB in its expanded range.

Physiological Status of Rice Leaf-Roller Cnaphalocrocis medinalis (Lepidoptera: Crambidae) Adults Trapped by Sex Pheromone and Floral Odor

The rice leaf-roller Cnaphalocrocis medinalis is an important migratory pest of rice. We conducted a study to determine the physiological status of adults trapped by a sex pheromone and floral odor. In the immigrant group, the number of males trapped by the floral odor was greater than the number caught by sex pheromone trapping. The volume of testes was similar in the above two trapping methods but was smaller than in the sweep net method. The ovary developmental grade, mating rate, and number of matings of females caught in floral odor trap were higher than in those caught in the sweep net. In the local breeding group, the number of males trapped by sex pheromones was greater than the number trapped by the floral odor. The volume of testes was smaller in the floral odor trap compared to the pheromone trap group, with the largest in the sweep net group. The ovarian developmental grade, mating rate, and number of matings of females were significantly higher in the floral odor trap group than in the sweep net group. In the emigrant group, the adult olfactory response to the sex pheromone and floral odor was low. The volume of testes was larger in the sweep net group compared to the moths caught by floral odor trapping. The number of eggs laid by female immigrants trapped by the floral odor and sweep net was similar, while the number in the local breeding group was greater in moths caught with the sweep net in comparison with those caught by the floral odor trap. The difference in egg hatchability between the two trapping methods in both immigrants and local breedings was not significant.

Plasticity of the olfactory behaviors in Bactrocera dorsalis under various physiological states and environmental conditions

Insects rely heavily on their olfactory system for various behaviors, including foraging, mating, and oviposition. Numerous studies have demonstrated that insects can adjust their olfactory behaviors in response to different physiological states and environmental conditions. This flexibility allows them to perceive and process odorants according to different conditions. The Oriental fruit fly, Bactrocera dorsalis, is a highly destructive and invasive pest causing significant economic losses to fruit and vegetable crops worldwide. The olfactory behavior of B. dorsalis exhibits strong plasticity, resulting in its successful invasion. To enhance our understanding of B. dorsalis' olfactory behavior and explore potential strategies for behavior control, we have reviewed recent literature on its olfactory plasticity and potential molecular mechanisms.

Fermented or Floral? Developing a Generalized Food Bait Lure to Monitor Cutworm and Armyworm Moths (Lepidoptera: Noctuidae) in Field Crops

Cutworms and armyworms (Lepidoptera: Noctuidae) are a pest complex in North America that cause sporadic damage in field crops on the Canadian Prairies; however, no methods have been developed to reliably monitor population densities. Food-based semiochemicals attract both sexes of adult moths and could be used to monitor multiple species with a single lure in a single trap. Here, we focus on enhancing the attractiveness of acetic acid and 3-methyl-1-butanol (AAMB) lures to redbacked cutworm (Euxoa ochrogaster) (RBC) and other noctuid pests. Experiments conducted in canola and wheat fields tested AAMB lures at different release rates, from different devices and in combination with other semiochemicals. High-release lures captured more females in canola, while low-release lures captured more males in wheat. Thus, crop volatiles may influence response to lures. Semiochemicals embedded in an inert matrix caught more RBC moths than semiochemicals released from Nalgene or polyethylene dispensers did. More RBC females were attracted to AAMB lures with 2-methyl-1-propanol than phenylacetaldehyde. Fermented volatiles appear to be a more reliable attractant than floral volatiles for these species. RBC moth antennae produced significant responses to all doses of phenylacetaldehyde tested in electroantennogram assays, but only to higher doses of acetic acid and 3-methyl-1-butanol. Physiological state of the RBC moths also influenced responsiveness to the tested semiochemical. Feeding status did not influence the antennal response to acetic acid and phenylacetaldehyde in either sex, but it increased the response to 3-methyl-1-butanol in females when fed. AAMB lures should be further developed to monitor RBC moths and other noctuid pests in field crops.

Plasticity in Chemical Host Plant Recognition in Herbivorous Insects and Its Implication for Pest Control

Chemical communication is very important in herbivorous insects, with many species being important agricultural pests. They often use olfactory cues to find their host plants at a distance and evaluate their suitability upon contact with non-volatile cues. Responses to such cues are modulated through interactions between various stimuli of biotic and abiotic origin. In addition, the response to the same stimulus can vary as a function of, for example, previous experience, age, mating state, sex, and morph. Here we summarize recent advances in the understanding of plant localization and recognition in herbivorous insects with a focus on the interplay between long- and short-range signals in a complex environment. We then describe recent findings illustrating different types of plasticity in insect plant choice behavior and the underlying neuronal mechanisms at different levels of the chemosensory pathway. In the context of strong efforts to replace synthetic insecticides with alternative pest control methods, understanding combined effects between long- and close-range chemical cues in herbivore-plant interactions and their complex environment in host choice are crucial to develop effective plant protection methods. Furthermore, plasticity of behavioral and neuronal responses to chemical cues needs to be taken into account to develop effective sustainable pest insect control through behavioral manipulation.

Effects of advanced age on olfactory response of male and female Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae)

Olfaction is an essential sensory modality of insects which is known to vary with age. In short-lived insects odour response generally declines rapidly with increasing age, but how increasing age affects the olfactory response of long-lived insects is less known and there may be different life-time patterns of olfactory response. Here, we examine the effect of age on olfactory response and exploratory activity of a long-lived tephritid fruit fly, Bactrocera tryoni from sexual maturity (3 weeks) to advanced age (15 weeks). Males were tested against a male-specific attractant, cue-lure, which is associated with courtship and sexual selection in this species; while females were tested against guava-juice, a highly attractive oviposition host fruit odour. Trials were done in the laboratory using a Y-tube olfactometer at three weekly intervals. The probability of olfactory response of both males and females to tested odours declined with age. Males retained a constant attraction to cue-lure until 12 weeks of age, but then showed a significant drop in olfactory response at 15 weeks. However, females showed the highest attraction to guava-juice odour until six weeks of age and declined gradually thereafter. The change on odour response over time can be associated with an age-related change in initial locomotor activity for females as there was no change, over the life of the experiment, in selective female orientation to the odour source once flies started exploring within the olfactometer. However, for 15 week-old males, there was a simultaneous drop in both locomotor activity and selective olfactory orientation. The consistent attraction of male to cue-lure might be related to life-long reproductive activities of males, as males are thought to mate continuously during life. On the other hand, females' highest attraction to guava-juice odour in early life followed by a gradual decline might be linked with their oviposition rate which peaks in early life.

Transcriptome analysis of antennal cytochrome P450s and their transcriptional responses to plant and locust volatiles in Locusta migratoria

Cytochrome P450 monooxygenases (P450s) constitute a large superfamily of heme-thiolate proteins that are involved in the biosynthesis or degradation of endogenous compounds and detoxification of exogenous chemicals. It has been reported that P450s could serve as odorant-degrading enzymes (ODEs) to inactivate odorants to avoid saturating the antennae. However, there is little information about P450s in the antennae of Locusta migratoria. In the current work, we conducted an antenna transcriptome analysis and identified 92 P450s, including 68 full-length and 24 partial sequences. Phylogenetic analysis showed that 68 full-length P450s were grouped into four clans: CYP2, CYP3, CYP4, and mitochondria clans. Tissue, stage, and sex-dependent expressions of these 68 P450s were investigated. The results showed that 4 P450s were antenna-specific, whereas others were antenna-rich but also expressed in other tissues, implying their various potential roles in the antennae. In addition, the responses of seven selected P450s to five gramineous plant volatiles and four locust volatiles were determined. CYP6MU1 could be induced by almost all compounds tested, suggesting its important roles in odorant processing. Different P450s exhibited diverse responses to odorants, indicating that specific regulation of P450 expression by odorants might modulate the sensitivity of the olfactory responses to various chemicals.

Context-Dependence and the Development of Push-Pull Approaches for Integrated Management of Drosophila suzukii

Sustainable pest control requires a systems approach, based on a thorough ecological understanding of an agro-ecosystem. Such fundamental understanding provides a basis for developing strategies to manipulate the pest’s behaviour, distribution, and population dynamics, to be employed for crop protection. This review focuses on the fundamental knowledge required for the development of an effective push-pull approach. Push-pull is a strategy to repel a pest from a crop, while attracting it toward an external location. It often relies on infochemicals (e.g., pheromones or allelochemicals) that are relevant in the ecology of the pest insect and can be exploited as lure or repellent. Importantly, responsiveness of insects to infochemicals is dependent on both the insect’s internal physiological state and external environmental conditions. This context-dependency reflects the integration of cues from different sensory modalities, the effect of mating and/or feeding status, as well as diurnal or seasonal rhythms. Furthermore, when the costs of responding to an infochemical outweigh the benefits, resistance can rapidly evolve. Here, we argue that profound knowledge on context-dependence is important for the development and implementation of push-pull approaches. We illustrate this by discussing the relevant fundamental knowledge on the invasive pest species Drosophila suzukii as an example.