Effects Of Antennal Sensilla On Locomotory Responses Of Three Stored-Product Pests And Chemosensory Gene Families Of Rhyzopertha Dominica (Coleoptera:Bostrichidae)

Rhyzopertha dominica (Fabricius), Tribolium castaneum (Herbst) and Sitophilus oryzae (Coleoptera:Curculionidae) are all economically important pests of stored products. Since the repeated use of pesticides increase incidence of resistance of the pests, integrated pest management is increasingly focused on the use of semiochemicals for protecting agricultural products. However host identification through odors in these three stored-product pests remains unclear. Insects have specialized chemosensory systems which detect stimuli from the external environment, and several soluble proteins are involved in the biochemical step of odour reception. Furthermore, genetic information about olfactory genes in these three stored product pests is scarce. In this study, the morphology of the antennal sensilla, and effects of sensilla on locomotory responses of three stored-product pests to host (wheat grain) were studied. The antennae were collected from both male and female of R. dominica to conduct transcriptome sequencing so that to identify genes involved in chemosensation in R. dominica. This approach can promote the understanding of the behavior essence of insects and plants, but also provide theories for controlling of these pests.1 Effect of antennal sensilla distribution pattern on feeding behavior of Rhyzopertha dominica (Coleoptera:Bostrichidae)Morphology and distribution pattern of the sensilla on antennal segments of male and female R. dominica were first investigated using scanning electron microscope (SEM) before performing two Y-tube bioassays. Morphologically, four types with one subtype of Sensilla basiconica (S. basiconca), three types with five subtypes of Sensilla trichodea (S. trichodea), five types and one subtype of Sensilla coeloconica (S. coeloconica) and one type of Sensilla cavity (S. cavity) and Sensilla styloconica (S. styloconica) were recorded on the antennae of male and female R. dominica. Sexual dimorphism was found in sensilla number, and S. cavity and S. styloconica were distributed in the antennae of male and female, respectively. Based on the results of the first bioassay, some compounds which Tridecanone, Ethyl-1-hexanol, Heptacosane, Hentriacontane, Acetophenone and (+)-3-carene were selected to run a second Y-tube experiment in which the last three segments of the antennae were removed. The results showed that by removing these terminal segments, the beetle spent more time before making a choice comparatively to those walking with complete antennal segments. The average time before removing the last three segments for male and female ranged from 1.52±0.13 to 2.51±0.21 and 1.47±0.16 to 2.89±0.33, respectively. And after removing these segments, the average time for male and female ranged 2.56±0.26 to 4.50±0.59 and 3.06±0.25 to 3.84±0.41, respectively.2 Effect of antennal sensilla distribution pattern on behavioral responses of Tribolium castaneum (Coleoptera:Tenebrionidae)The morphology and distribution pattern of sensilla on the antennal flagella of male and female T. castaneum were first investigated using SEM before performing Y-tube bioassays. Thorough observation of the data showed no sexual dimorphism sensilla morphology and distribution in both genders. Three morphological types of sensilla were recorded:Sensilla trichodea with two subtypes, seven types of Sensilla basiconica and two types of Sensilla cavity. S. trichodea were distributed on all antennal segments, but were much more on the last three segments; in contrast to ST, S. basiconica were found exclusively on the last three segments, while S. cavity was especially founded on particular segments of the antennae.Female and male T. castaneum exhibited broad overlap in their behavior responses to various odors. Sexual preference for some volatiles was noticed, but after removing the three terminal antennal segments there was no significant preference for any compounds including those who revealed more attractive in the previous biossay in which the beetle were tested with the entire antennal segments. In order words, like R. dominica, by removing the last three segments of the antennae the beetle spent significantly the time before making a choice. The average time before removing the last three segments for male and female ranged from 1.19±0.10 to 1.57±0.16 and 1.08±0.10 to 1.54±0.18, respectively. And after removing these segments, the average time for male and female ranged 3.06±0.25 to 3.84±0.41 and 1.95±0.23 to 3.29±0.23, respectively.3 Ultrastructural observations of the antennal sensilla of Sitophilus oryzaeLikely, like the two previous pests, here also, the morphology and distribution pattern of the sensilla on the antennae of male and female S. oryzae were investigated using scanning electron microscope. Morphologically, the antennae of S. oryzae bore 5 types of Sensilla chaetica (S. chaetica) with 1 subtype,2 types of Sensilla basiconica with two subtypes and 4 types of Sensilla coeloconica. Like R. dominica and T castaneum, some S. cavities were found in S. oryzae too with no sexual dimorphism. But an uncountable number of S. cavities were found on the rostrum comparatively to the antennae. Bioassay test has not been performed for S. oryzae, because the Y-tube used in the experiment was found undesirable for that pest.4 De novo analysis of R. dominica antennal transcriptomeWe conducted the antennal transcriptome sequencing of R. dominica and described the olfactory gene families. The data showed 57 million 90-bp-long reads which were then assembled into 37,877 unigenes with a mean size of 456 bp. Among the antennal transcripts,19.7 showed significant similarity (E-value< le-5) to known proteins at NCBI database. Gene ontology and KEGG analyses were performed to classify the gene functions in R. dominica antenna. After thorough analysis,13 putative odorant binding proteins (OBPs),8 chemosensory proteins (CSPs),5 sensory neuron membrane proteins (SNMPs),5 odorant receptors (Ors),9 ionotropic receptors (IRs),13 chemosensory receptors,159 cytochrome P450,19 pheromone-degrading enzymes,31 carboxylesterase, and 48 glutathione S-transferase were identified. The predicted protein sequences were compared with counterparts Tribolium castaneum (79.1%), Dondroctonus ponderasea (1.7%), Megachile rotundata (1.2%), Acyrthoshiphon pisun (1.2%) and others (16.7%). The present data could provide comprehensive olfactory gene-expression information for further understanding of the behavior of R. dominica.