Characterization of the complete mitochondrial genome of a barklouse, Lepinotus sp. (Psocodea: Trogiomorpha: Trogiidae).

Barklice in the genus Lepinotus (Psocoptera: Trogiidae) are small, soft-bodied stored-product pests that are difficult to control. We sequenced and annotated the mitochondrial (mt) genome of Lepinotus sp. The mt genome of Lepinotus sp. is 16,299 bp in size with 74.4% A + T content. The gene order was highly conserved in some of the Trogimorpha barklice. Two types of tandem repeat units were identified in CR of Lepinotus sp. The phylogenetic analysis showed that Trogiidae species was the sister group to Lepidopsocidae barklice, and the suborder Troctomorpha was polyphyletic.

Antioxidant Enzymes and Heat Shock Protein Genes from Liposcelis bostrychophila Are Involved in Stress Defense upon Heat Shock.

Psocids are a new risk for global food security and safety because they are significant worldwide pests of stored products. Among these psocids, Liposcelis bostrychophila has developed high levels of resistance or tolerance to heat treatment in grain storage systems, and thus has led to investigation of molecular mechanisms underlying heat tolerance in this pest. In this study, the time-related effects of thermal stress treatments at relatively high temperatures on the activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidases (POD), glutathione-S-transferases (GST) and malondialdehyde (MDA), of L. bostrychophila were determined. Thermal stress resulted that L. bostrychophila had a significantly higher MDA concentration at 42.5 °C, which indicated that the heat stress increased lipid peroxidation (LPO) contents and oxidative stress in this psocid pest. Heat stress also resulted in significant elevation of SOD, CAT and GST activities but decreased POD activity. Our data indicates that different antioxidant enzymes contribute to defense mechanisms, counteracting oxidative damage in varying levels. POD play minor roles in scavenging deleterious LPO, while enhanced SOD, CAT and GST activities in response to thermal stress likely play a more important role against oxidative damage. Here, we firstly identified five LbHsps (four LbHsp70s and one LbHsp110) from psocids, and most of these LbHsps (except LbHsp70-1) are highly expressed at fourth instar nymph and adults, and LbHsp70-1 likely presents as a cognate form of HSP due to its non-significant changes of expression. Most LbHsp70s (except LbHsp70-4) are significantly induced at moderate high temperatures (<40 °C) and decreased at extreme high temperatures (40-45 °C), but LbHsp110-1 can be significantly induced at all high temperatures. Results of this study suggest that the LbHsp70s and LbHsp110 genes are involved in tolerance to thermal stress in L. bostrychophila, and antioxidant enzymes and heat shock proteins may be coordinately involved in the tolerance to thermal stress in psocids.

Characterization of Esterase Genes Involving Malathion Detoxification and Establishment of an RNA Interference Method in Liposcelis bostrychophila.

Esterases (ESTs) play important roles in metabolizing various physiologically endogenous and exogenous compounds, and various environmental xenobiotics in insects. The psocid, Liposcelis bostrychophila is a major pest of stored products worldwide and rapidly develops resistance to commonly insecticides. However, the involvement of ESTs in insecticide metabolization and the application of RNAi approach in psocids have not been well elucidated. In this study, we characterized four LbEST genes and investigated the transcriptional levels of these genes at different developmental stages and under different insecticides exposures to assess their potential roles in response to insecticides. The four LbESTs contain a catalytic triad (Ser-His-Glu) linked to an oxyanion hole and acyl pocket involved in substrate stabilization during its hydrolysis. Synergism observed with the esterase-inhibitor DEF suggests the involvement of esterases in malathion detoxification. LbESTs were expressed during the whole of developmental stages, but predominant abundance in the first nymphal instar and adult stage. The mRNA level of three LbEST genes (except for LbEST4) was induced (1.29- to 5.60 fold) in response to malathion or deltamethrin exposures, indicating that these esterases are involved in the detoxification process. Silencing of LbEST1, LbEST2 or LbEST3 through dsRNA feeding led to a higher mortality of psocids upon the malathion treatment compared to controls (1.83 to 2.69-fold), demonstrating that these esterase genes play roles in malathion detoxification in L. bostrychophila. Our study provides new evidence for understanding of the function and regulation mechanism of esterases in L. bostrychophila in insecticide detoxification. The current study also suggests that the present RNAi method could be applied for gene functional studies in psocids.

The mitochondrial genome of the brown citrus aphid Aphis (Toxoptera) citricidus: Insights into the repeat regions in aphids and phylogenetic implications.

We sequenced the complete mitochondrial (mt) genome of brown citrus aphid, Aphis (Toxoptera) citricidus (Kirkaldy) and compared it with that of other aphids. The mt genome of A. citricidus is a circular molecule of 16,763 bp with 84.0% AT content, containing 13 protein-coding genes (PCGs), 2 rRNAs, 22 tRNAs, a control region (CR) and an additional repeat region between trnE and trnF. Like other aphids, A. citricidus was slightly A-skewed (0.073) and strongly C-skewed (-0.309). Most PCGs used standard ATW start codons and TAA stop codons except nad4, which terminates with an incomplete codon T. All tRNAs and rRNA could be folded as typical secondary structures, except for lacking a dihydrouridine (DHU) arm in tRNASer (AGN). The repeat region possessed the most copy number of repeat motif (~7.5 times) among the reported aphid mt genomes, like in Acyrthosiphon pisum. Both Bayesian inference (BI) and Maximum likelihood (ML) analyses suggested that Toxoptera citricidus should revert to Aphis citricidus. The subfamily Aphidinae is monophyletic, but the Eriosomatinae is non-monophyletic. This study provides new insight into the evolution of aphid mt genomes, as well as useful information for resolving aphid phylogenetic questions.