Insight Into the Ultrastructure of Antennal Sensilla of Mythimna separata (Lepidoptera: Noctuidae).

The oriental armyworm, Mythimna separata (Walk), is one of the most serious pests of cereals in Asia and Australasia. The structure and distribution of the antennal sensilla of M. separata were studied by scanning electron microscopy and transmission electron microscopy. The results showed that antennae of both female and male M. separata are filiform in shape. Three groups and seven morphological sensillum types were recorded in both sexes, including uniporous sensilla (sensilla chaetica), multiporous sensilla (sensilla trichodea, basiconica, coeloconica, and styloconica), and aporous sensilla (sensilla squamiformia and Böhm bristles). S. trichodea, which were the most abundant sensilla, was made of three subtypes (ST I, ST II, and ST III) according to external features and two subtypes of s. basiconica (SB I and SB II) and s. coeloconica (SCo I and SCo II) were identified, respectively. Sexual dimorphisms in sensilla of M. separata were mainly perceived as the variations in the numbers of several sensilla subtypes. Also, the possible functions of the antennal sensilla were discussed. These results contribute to our understanding of the function of antennae in the behavior of M. separata.

Transcriptomic Analysis of Resistant and Wild-Type Isolates Revealed Fludioxonil as a Candidate for Controlling the Emerging Isoprothiolane Resistant Populations of Magnaporthe oryzae.

The point mutation R343W in MoIRR, a putative Zn2Cys6 transcription factor, introduces isoprothiolane (IPT) resistance in Magnaporthe oryzae. However, the function of MoIRR has not been characterized. In this study, the function of MoIRR was investigated by subcellular localization observation, transcriptional autoactivation test, and transcriptomic analysis. As expected, GFP-tagged MoIRR was translocated in the nucleus, and its C-terminal could autonomously activate the expression of reporter genes HIS3 and α-galactosidase in absence of any prey proteins in Y2HGold, suggesting that MoIRR was a typical transcription factor. Transcriptomic analysis was then performed for resistant mutant 1a_mut (R343W), knockout transformant ΔMoIRR-1, and their parental wild-type isolate H08-1a. Upregulated genes in both 1a_mut and ΔMoIRR-1 were involved in fungicide resistance-related KEGG pathways, including the glycerophospholipid metabolism and Hog1 MAPK pathways. All MoIRR deficiency-related IPT-resistant strains exhibited increased susceptibility to fludioxonil (FLU) that was due to the upregulation of Hog1 MAPK pathway genes. The results indicated a correlation between FLU susceptibility and MoIRR deficiency-related IPT resistance in M. oryzae. Thus, using a mixture of IPT and FLU could be a strategy to manage the IPT-resistant populations of M. oryzae in rice fields.

Climate warming promotes pesticide resistance through expanding overwintering range of a global pest.

Climate change has the potential to change the distribution of pests globally and their resistance to pesticides, thereby threatening global food security in the 21st century. However, predicting where these changes occur and how they will influence current pest control efforts is a challenge. Using experimentally parameterised and field-tested models, we show that climate change over the past 50 years increased the overwintering range of a global agricultural insect pest, the diamondback moth (Plutella xylostella), by ~2.4 million km2 worldwide. Our analysis of global data sets revealed that pesticide resistance levels are linked to the species' overwintering range: mean pesticide resistance was 158 times higher in overwintering sites compared to sites with only seasonal occurrence. By facilitating local persistence all year round, climate change can promote and expand pesticide resistance of this destructive species globally. These ecological and evolutionary changes would severely impede effectiveness of current pest control efforts and potentially cause large economic losses.

A chemosensory protein MsepCSP5 involved in chemoreception of oriental armyworm Mythimna separata.

Chemosensory proteins (CSPs) have been suggested to perform several functions in insects, including chemoreception. To find out whether MsepCSP5 identified from Mythimna separata shows potential physiological functions in olfaction, gene expression profiles, ligand-binding experiments, molecular docking, RNA interference, and behavioral test were performed. Results showed that MsepCSP5 was highly expressed in female antennae. MsepCSP5 showed high binding affinities to a wide range of host-related semiochemicals, and displayed that 26 out of 35 candidate volatiles were highly bound (Ki < 10 µM) at pH 5.0 rather than pH 7.4. The binding sites of MsepCSP5 to candidate volatiles were well predicted by three-dimensional structure modeling and molecular docking experiments. Pursuing further, biological activities of M. separata to highly bound compounds elicited strong behavioral responses, such as alcoholic compounds displayed strong attractiveness whereas terpenes showed repellency to M. separata. The transcript expression level of MsepCSP5 gene significantly decreased after injecting target dsRNAs, and resulted in non-significant preference responses of M. separata to semiochemicals, such as 3-pentanol and 1-octene-3-ol. In conclusion, MsepCSP5 may involve in semiochemical reception of M. separata.

De novo analysis of the oriental armyworm Mythimna separata antennal transcriptome and expression patterns of odorant-binding proteins.

To better understand the olfactory mechanisms in the oriental armyworm Mythimna separate, one of the most serious pests of cereals, an antennal transcriptome was constructed in this study. A total of 130 olfactory related transcripts were identified. These transcripts were predicted to encode 32 odorant-binding proteins (OBPs), 16 chemosensory proteins (CSPs), 71 olfactory receptors (ORs), 8 ionotropic receptors (IRs), 1 gustatory receptor (GR) and 2 sensory neuron membrane proteins (SNMPs). Q-PCR analysis of the temporal expression profiles of seven OBPs in different tissues indicated that, except for MsepOBP19 which was highly expressed in the wings of 0-day-old adult and MsepOBP20 which was low expressed in all tissues, other tested MsepOBPs were significantly more highly expressed in the antenna than in the head (antenna excluded), thorax, abdomen, legs and wings. The expression levels of MsepOBPs were diverse in different life stages (differed on eclosion days). MsepOBP5 exhibited female-biased expression in 0- and 5-day-old adult, while no gender bias in 1- and 3-day-old adult was detected and similar expression profiles were found for MsepOBP7, 20, 24 and 26. In addition, we found that although the expression of MsepOBP22 was female biased in 0- and 5-day-old adult, in the 3-day-old adult it was male-biased. Our findings established a foundation for future studies of the functions of olfactory proteins in M. separata.

Impact of hot events at different developmental stages of a moth: the closer to adult stage, the less reproductive output.

Hot days in summer (involving a few hours at particularly high temperatures) are expected to become more common under climate change. How such events at different life stages affect survival and reproduction remains unclear in most organisms. Here, we investigated how an exposure to 40 °C at different life stages in the global insect pest, Plutella xylostella, affects immediate survival, subsequent survival and reproductive output. First-instar larvae showed the lowest survival under heat stress, whereas 3rd-instar larvae were relatively heat resistant. Heat exposure at the 1(st)-instar or egg stage did not influence subsequent maturation success, while exposure at the 3rd-instar larval stage did have an effect. We found that heat stress at developmental stages closer to adult stage caused greater detrimental effects on reproduction than heat stress experienced at earlier life stages. The effects of hot events on insect populations can therefore depend critically on the timing of the event relative to an organism's life-cycle.

[Thermal tolerance of diamondback moth Plutella xylostella].

Diamondback moth Plutella xylostella is a worldwide important pest on cruciferous vegetables. Critical thermal maximum (CTMax) is often used as an index for the thermal tolerance of insects. By the method of dynamic heating, this paper measured the CTMax of P. xylostella in a self-assembled device, and studied the effects of development stage, rearing temperature, generation, sex, and heat shock on the thermal tolerance of P. xylostella based on the CTMax values. Reared at 25 degrees C, the mean CTMax of the 4th larva (50.31 degrees C) was significantly higher than that of the 1st larva (43.03 degrees C), 2nd larva (46.39 degrees C), 3rd larva (49.67 degrees C), female adult (45.76 degrees C), and male adult (47.73 degrees C); reared at 20, 25, and 30 degrees C, the adults had no significant difference in their CTMax; reared at 30 degrees C for 1-, 3-, and 6 generations, the CTMax of the adults also had no significant difference. In all the treatments, the CTMax of the female and male adults had less difference. Heat shock with 40 degrees C for 45 minutes could make the CTMax of 5 day-old male moth increased from 45.51 degrees C to 46.49 degrees C.