Chemosensory Receptor Expression in the Abdomen Tip of the Female Codling Moth, Cydia pomonella L. (Lepidoptera: Tortricidae).

In insects, the chemical senses influence most vital behaviors, including mate seeking and egg laying; these sensory modalities are predominantly governed by odorant receptors (ORs), ionotropic receptors (IRs), and gustatory receptors (GRs). The codling moth, Cydia pomonella, is a global pest of apple, pear, and walnut, and semiochemically based management strategies limit the economic impacts of this species. The previous report of expression of a candidate pheromone-responsive OR in female codling moth ovipositor and pheromone glands raises further questions about the chemosensory capacity of these organs. With an RNA-sequencing approach, we examined chemoreceptors' expression in the female codling moth abdomen tip, sampling tissues from mated and unmated females and pupae. We report 37 ORs, 22 GRs, and 18 IRs expressed in our transcriptome showing overlap with receptors expressed in adult antennae as well as non-antennal candidate receptors. A quantitative PCR approach was also taken to assess the effect of mating on OR expression in adult female moths, revealing a few genes to be upregulated or downregulating after mating. These results provide a better understanding of the chemosensory role of codling moth female abdomen tip organs in female-specific behaviors. Future research will determine the function of specific receptors to augment current semiochemical-based strategies for codling moth management.

Comparative transcriptomic assessment of the chemosensory receptor repertoire of Drosophila suzukii adult and larval olfactory organs.

The spotted wing Drosophila, Drosophila suzukii, has emerged within the past decade as an invasive species on a global scale, and is one of the most economically important pests in fruit and berry production in Europe and North America. Insect ecology, to a strong degree, depends on the chemosensory modalities of smell and taste. Extensive research on the sensory receptors of the olfactory and gustatory systems in Drosophila melanogaster provide an excellent frame of reference to better understand the fundamentals of the chemosensory systems of D. suzukii. This knowledge may enhance the development of semiochemicals for sustainable management of D. suzukii, which is urgently needed. Here, using a transcriptomic approach we report the chemosensory receptor expression profiles in D. suzukii female and male antennae, and for the first time, in larval heads including the dorsal organ that houses larval olfactory sensory neurons. In D. suzukii adults, we generally observed a lack of sexually dimorphic expression levels in male and female antennae. While there was generally conservation of antennal expression of odorant and ionotropic receptor orthologues for D. melanogaster and D. suzukii, gustatory receptors showed more distinct species-specific profiles. In larval head tissues, for all three receptor gene families, there was also a greater degree of species-specific gene expression patterns. Analysis of chemosensory receptor repertoires in the pest species, D. suzukii relative to those of the genetic model D. melanogaster enables comparative studies of the chemosensory, physiology, and ecology of D. suzukii.

Alternative Splicing of the CpomOR53 Gene Produces Three Transcripts Expressed in Codling Moth (Lepidoptera: Tortricidae) Antennae.

Incorporation of semiochemicals into codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), IPM programs has drastically reduced the amount of chemical insecticides needed to control this orchard pest. Odorant receptors are key sensors in the detection of semiochemicals and trigger downstream signaling events leading to behavioral responses. For codling moth, 58 odorant receptors have been identified in antennal transcriptomes, a few of which have been characterized for ligand activation. From the codling moth antennal transcriptome, a single transcript encoding CpomOR53 was annotated but re-evaluation suggests two or more variants of this receptor may be present and it is hypothesized that they are produced by alternative splicing. In this study, the complete open reading frame of CpomOR53 was amplified from codling moth male and female antennal RNAs, with three distinct transcripts detected. Characterization of these transcripts indicate that they are produced by alternative splicing of the CpomOR53 gene. The membrane topology for each of the CpomOR53 variants shows that alternative spliced products altered the length of intracellular loop two of the predicted proteins. The effects of these alterations were not determined but will be addressed in future studies determining the ligand(s) that activate each CpomOR53 transcript variant.