Investigating Photo-Degradation as a Potential Pheromone Production Pathway in Spotted Lanternfly, Lycorma delicatula

Abstract

Since its discovery in North America in 2014, the spotted lanternfly (SLF), Lycorma delicatula, has become an economic, ecological, and nuisance pest there. Developing early detection and monitoring tools is critical to their mitigation and control. Previous research found evidence that SLF may use pheromones to help locate each other for aggregation or mating. Pheromone production necessitates specific conditions by the insects, and these must be investigated and described. A chemical process called photo-degradation has been described as a final step in the production of pheromones in several diurnal insect species, in which cuticular hydrocarbons were broken down by sunlight into volatile pheromone components. In this study, photo-degradation was investigated as a possible pheromone production pathway for SLF. Extracts from SLF mixed-sex third and fourth nymphs and male or female adults were either exposed to simulated sunlight to produce a photo-degradative reaction (photo-degraded), or not exposed to light (crude), while volatiles were collected. Behavioral bioassays tested for attraction to volatiles from photo-degraded and crude samples and their residues. In third instars, only the volatile samples from photo-degraded mixed-sex extracts were attractive. Fourth instar males were attracted to both crude and photo-degraded residues, and volatiles of photo-degraded mixed-sex extracts. Fourth instar females were attracted to volatiles of crude and photo-degraded mixed-sex extracts, but not to residues. In adults, only males were attracted to body volatiles from crude and photo-degraded extracts of either sex. Examination of all volatile samples using gas chromatography coupled with mass spectrometry (GC-MS) revealed that most of the identified compounds in photo-degraded extracts were also present in crude extracts. However, the abundance of these compounds in photo-degraded samples were 10 to 250 times more than their abundance in the crude counterparts. Results from behavioral bioassays indicate that photo-degradation probably does not generate a long-range pheromone, but it may be involved in the production of a short-range sex-recognition pheromone in SLF. This study provides additional evidence of pheromonal activity in SLF.

Antennal Sensitivity of Spotted Lanternflies, Lycorma delicatula: Differential Electrophysiological Responses of Males and Females to Compounds Derived from Host Plants and Conspecifics

“…Authentic volatile compounds found in three odor sources were tested on the SLF antennae of fourth-instar and adult males and females. The sources were host plant volatiles [ 18 ], SLF honeydew volatiles [ 16 ], and SLF body volatiles from whole-body extracts [ 20 ]. The SLF honeydew-related volatiles were benzyl acetate (≥99%), 1-dodecanol (98%), 2-phenyl ethanol (≥99%), nonyl acetate (≥97%), decyl acetate (≥95%), and 2-ethylhexyl acetate (≥99%).…”

“…The development of effective semiochemical-based monitoring tools for SLF is an objective of our research [ 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. However, due to the large number of volatile compounds identified from SLF host plants, their honeydew, and body volatiles [ 16 , 18 , 19 , 20 ], there are too many individual compounds and potential blends to practically test, especially given the constraints of SLF being univoltine and lacking artificial rearing capabilities. EAG experiments revealed that a subset of these compounds could be detected by SLF antennae, with both male and female antennae capable of detecting the same set of compounds.…”

“…EAG experiments revealed that a subset of these compounds could be detected by SLF antennae, with both male and female antennae capable of detecting the same set of compounds. A subset of those antennally active compounds was tested in bioassays and found to elicit behavioral responses, although they generated different responses among stages and sexes [ 16 , 18 , 19 , 20 ]. However, the list of antennally active compounds still contains an impractical number of compounds to test for attraction individually and in blends.…”

“…In the current study, we screened and compared the EAG responses of antennae from fourth-instar and adult SLF males and females to a series of authentic compounds that had been previously identified from host plants [ 18 ] and conspecific volatiles [ 16 , 20 ], presented at fixed doses. SLF males and females have similar diets and host plants [ 18 , 21 ], so we expected both male and female antennae to respond similarly to compounds from host plants.…”

“…SLF males and females have similar diets and host plants [ 18 , 21 ], so we expected both male and female antennae to respond similarly to compounds from host plants. Based on previous dual-choice olfactometer studies, in which SLF were offered a choice between conspecific body volatiles or controls, where only males, but not females, were attracted to these volatiles [ 20 ], we hypothesized that SLF male antennae may be more sensitive, and, thus, produce larger EAG responses to conspecific compounds than female antennae. We also tested a subset of chemicals in an EAG dose–response experiment to look for differences in dose response among several compounds with different functional groups (alcohol, aldehyde, ester, and ketone).…”