Cheyletus malaccensis Oudemans is a predatory mite inhabiting grain depots in China. The relationship between temperature and the population growth rate of C. malaccensis is useful for predicting its population dynamics. Age-stage, two-sex life tables of the predator, C. malaccensis, reared on Acarus siro were constructed under laboratory conditions at 22, 24, 28, 30, and 32 °C, 75% relative humidity, and a 0:24 h (L:D) photoperiod. Increasing temperature shortened the development time of the immature stages. The complete generation time of C. malaccensis ranged from 11.10 d to 27.50 d. Life table parameters showed that 28 °C was the optimum temperature for the growth and development of C. malaccensis; populations could increase rapidly at this temperature. The highest net reproductive rate (R₀ = 290.25) and highest fecundity (544.52) occurred at 28 °C. Temperature significantly affected the intrinsic rate of increase (r), fecundity, and finite rate of increase (λ). The values of age-specific fecundity (high to low) were 28 °C > 24 °C > 30 °C > 32 °C > 22 °C, while the values of age-stage-specific fecundity had the same trend.

Thermal treatment has been extensively used to control pests in stored grains for a long time. The objective of this study was to analyze thermal death kinetics of adult flat grain beetle, Cryptolestes pusillus (Schonherr), lesser grain borer, Rhyzopertha dominica (Fabricius), and confused flour beetle, Tribolium confusum (Jacquelin du Val), using a heating block system (HBS), at temperatures of 46, 48, 50, and 52 °C for C. pusillus and T. confusum, and 48, 50, 52, and 54 °C for R. dominica with a heating rate of 5 °C/min. Thermal death curves of those three insects followed a 0th-order reaction model. Complete mortality of C. pusillus, R. dominica, and T. confusum were observed after exposure to 1.4, 5.0, and 0.9 min at 52, 54 and 52 °C, respectively. The thermal death activation energy for controlling C. pusillus, R. dominica, and T. confusum was 689.91, 380.88, and 617.08 kJ/mol with z values of 2.88, 5.18, and 3.22 °C, respectively. The cumulative lethal time model can also be used to predict mortality of these three insects during a practical heating process. The information provided by this study on storage pests may be useful for developing effective thermal treatment protocols.

Background: The lesser grain borer (Rhyzopertha dominica), a worldwide primary pest of stored grain, causes serious economic losses and threatens stored food safety. R. dominica can respond to changes in temperature, especially the adaptability to heat. In this study, transcriptome analysis of R. dominica exposed to different temperatures was performed to elucidate differences in gene expression and the underling molecular mechanism. Results: Isoform-sequencing generated 17,721,200 raw reads and yielded 20,416 full-length transcripts. A total of 18,880 (92.48%) transcripts were annotated. We extracted RNA from R. dominica reared at 5 °C (cold stress), 15 °C (cold stress), 27 °C (ambient temperature) and 40 °C (heat stress) for RNA-seq. Compared to those of control insects reared at 27 °C, 119, 342, and 875 differentially expressed genes (DEGs) were identified at 5 °C, 15 °C, and 40 °C, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that pathways associated with “fatty acid metabolism”, “fatty acid biosynthesis”, “AMPK signaling pathway”, “neuroactive ligand receptor interaction”, and “longevity regulating pathway-multiple species” were significantly enriched. The functional annotation revealed that the genes encoding heat shock proteins (HSPs), fatty acid synthase (FAS), phospholipases (PLA), trehalose transporter (TPST), trehalose 6-phosphate synthase (TPS), and vitellogenin (Vg) were most likely involved in temperature regulation, which was also validated by RT-qPCR. Seven candidate genes (rdhsp1, rdfas1, rdpla1, rdtpst1, rdtps1, rdvg1, and rdP450) were silenced in the RNA interference (RNAi) assay. RNAi of each candidate gene suggested that inhibiting rdtps1 expression significantly decreased the trehalose level and survival rate of R. dominica at 40 °C. Conclusions: These results indicated that trehalose contributes to the high temperature resistance of R. dominica. Our study elucidates the molecular mechanisms underlying heat tolerance and provides a potential target for the pest management in R. dominica.

Cheyletus malaccensis Oudemans and Cheyletus eruditus (Schrank) are predators of stored-grain pests in China. The psocid Liposcelis bostrychophila Badonnel is prone to outbreaks in depots. To assess the potential of large-scale breeding with Acarus siro Linnaeus and the biological control potential of C. malaccensis and C. eruditus against L. bostrychophila, we determined the development times of different stages at 16, 20, 24, and 28 °C and 75% relative humidity (RH) while feeding on A. siro, as well as the functional responses of both species’ protonymphs and females to L. bostrychophila eggs at 28 °C and 75% RH. Cheyletus malaccensis had a shorter development time and longer adult survival time than C. eruditus at 28 °C and 75% RH and could establish populations faster than C. eruditus while preying on A. siro. The protonymphs of both species showed a type II functional response, while the females showed a type III functional response. Cheyletus malaccensis showed a higher predation ability than C. eruditus, and the females of both species had a higher predation ability than the protonymphs. Based on the observed development times, adult survival times, and predation efficiency, Cheyletus malaccensis has much greater biocontrol potential than C. eruditus.

Rhyzopertha dominica is a serious stored grain insect pest around the world. Real-time quantitative polymerase chain reaction (RT-qPCR) is a widely used experimental method in molecular biology for detecting the expression of target genes. As appropriate reference genes are essential for normalizing gene expression, the selection of suitable reference genes is the basis of RT-qPCR experiments. In this study, the expression profiles of 7 candidate reference genes of rps3, rps6, rps13, actin, gadph, tubulin, and 18S rRNA were analyzed under 4 different experimental conditions. The expression stability of candidate genes was evaluated using the ΔCt, GeNorm, BestKeeper, NormFinder, and RefFinder methods. The results revealed that different reference genes were suitable for various experiments. Specifically, rps3 and rps6 were appropriate for the developmental stages and all samples: 18S rRNA and rps13 for temperature-related experiments, actin and rps6 for sex-related experiments, and rps6 and gadph for starvation stress. Our results lay essential groundwork for the normalization of RT-qPCR analyses and contribute to genomic and gene functional research of R. dominica.