Functional characterization of a geranylgeranyl diphosphate synthase in the leaf beetle Monolepta hieroglyphica.

Geranylgeranyl diphosphate synthase (GGPPS) as the short-chain prenyltransferases for catalyzing the formation of the acyclic precursor (E)-GGPP has been extensively investigated in mammals, plants, and microbes, but its functional plasticity is poorly understood in insect species. Here, a single GGPPS in leaf beetle Monolepta hieroglyphica, MhieGGPPS, was functionally investigated. Phylogenetic analysis showed that MhieGGPPS was clustered in one clade with homologs and had six conserved motifs. Molecular docking results indicated that binding sites of dimethylallyl diphosphate (DMAPP), (E)-geranyl pyrophosphate (GPP), and (E)-farnesyl pyrophosphate (FPP) were in the chain-length determination region of MhieGGPPS, respectively. In vitro, recombiant MhieGGPPS could catalyze the formation of (E)-geranylgeraniol against different combinations of substrates including isopentenyl pyrophosphate (IPP)/DMAPP, IPP/(E)-GPP, and IPP/(E)-FPP, suggesting that MhieGGPPS could not only use (E)-FPP but also (E)-GPP and DMAPP as the allylic cosubstrates. In kinetic analysis, the (E)-FPP was most tightly bound to MhieGGPPS than that of others. It was proposed that MhieGGPPS as a multifunctional enzyme is differentiated from the other GGPPSs in the animals and plants, which only accepted (E)-FPP as the allylic cosubstrate. These findings provide valuable insights into understanding the functional plasticity of GGPPS in M. hieroglyphica and the novel biosynthesis mechanism in the isoprenoid pathway.

Voltine Ecotypes of the Asian Corn Borer and Their Response to Climate Warming.

In the Asian corn borer (ACB), Ostrinia furnacalis (Guenée), diapause is governed by a multigenetic constitution that responds to daylength and temperature with seasonality. The ACB displays uni- or multivoltinism, depending on its geographic specificity. Hence, warmer temperatures may result in alternation of voltinism in the ACB, which will help in understanding the ecological consequences of climate warming on insects. In the present study, we investigated the voltinism in two natural populations from Harbin (H) and Gongzhuling (G) as well as a laboratory (L) population (established from the H population in 2017) of the ACB, at ambient and elevated atmospheric CO2 (aCO2 390 µL/L and eCO2 750 µL/L) and temperature (aT and Et = At + 2 °C). From the diapause response, both the uni- and multivoltine ecotypes were coexisting in the H population. The neonate occurrence date of 50% individuals that induced diapause was ca. 10 days later in the G population than in the H population, but it was about 10 days earlier than in the L population. Comparing to the dates of onset and the peak of diapause induction, the G and L populations were less variable than the H population in response to a short and/or shortening daylength in the field. The univoltine individuals could not be eliminated completely after 19 generations of selection. Diapause incidence decreased with a climate-warming scenario, which was temporally specific and could be overridden by significantly low daily average temperatures. The eCO2 did not directly impact the voltinism. On the basis of voltinism, the H population was sympatric for uni- and multivoltine ecotypes, with multivoltinism being dominant. The univoltinism trait was recessive. Climate warming could significantly override the effect of photoperiod, which was yearly dependent. Warmer temperatures and a decreased latitude (shortened daylength), and their interaction, would drive ACB evolution toward diapause homogeneity for multivoltinism.

Effects of Wolbachia on mitochondrial DNA variation in populations of Athetis lepigone (Lepidoptera: Noctuidae) in China.

Wolbachia are endosymbiotic bacteria that infect arthropods and incompatibility among strains can affect gene flow within host insect populations that can significantly result in host mitochondrial DNA (MtDNA) variation within or among populations. The effects of Wolbachia infection on Athetis lepigone MtDNA variation were studied across 12 geographical populations sampled from North China. Mitochondrial COI gene and Wolbachia wsp gene were both obtained from 423 individuals, including 46 Wolbachia infected and 377 uninfected individuals. Average A. lepigone infection rate was 11% (range: 0 to 26%), and wsp sequence variation defined three distinct Wolbachia strains; wLep1, wLep2, and wLep3, respectively. A haplotype network showed no relationship between A. lepigone MtDNA haplotype and Wolbachia infection. Furthermore, haplotype variation mainly exists within populations, although the proportion of variation is higher within uninfected compared to infected individuals. The lack of correlation between A. lepigone haplotype and Wolbachia strain, suggests symbiont infection may not affect mating compatibility or gene flow within host populations in China.

Does Bt maize expressing Cry1Ac protein have adverse effects on the parasitoid Macrocentrus cingulum (Hymenoptera: Braconidae)?

The potential effects of insect-resistant, genetically engineered (GE) crops on non-target organisms, especially on predators and parasitoids, must be evaluated before their commercial cultivation. The effects of GE maize that produces Cry1Ac toxin on the parasitoid Macrocentrus cingulum were assessed by direct bioassay and indirect bioassay. In the indirect bioassay, parasitism rate, cocoon weight and the number of M. cingulum progeny produced per host were significantly reduced when M. cingulum-parasitized Cry1Ac-susceptible Ostrinia furnacalis were fed a diet containing purified Cry1Ac; however, life-table parameters of M. cingulum were not adversely affected when the same assay was performed with Cry1Ac-resistant O. furnacalis. These results indicated that the detrimental effects detected with a Cry1Ac-susceptible host were mediated by poor host quality. In a direct bioassay, no difference in life-table parameters were detected when M. cingulum adults were directly fed a 20% honey solution with or without Cry1Ac; however, survival and longevity were significantly reduced when M. cingulum adults were fed a honey solution containing potassium arsenate, which was used as a positive control. The stability and bioactivity of Cry1Ac toxin in the food sources and Cry1Ac toxin uptake by the host insect and parasitoid were confirmed by enzyme-linked immunosorbent assay and sensitive-insect bioassays. Our results demonstrate that M. cingulum is not sensitive to Cry1Ac toxin at concentrations exceeding those encountered in Bacillus thuringiensis maize fields. This study also demonstrates the power of using resistant hosts when assessing the risk of genetically modified plants on non-target organisms and will be useful for assessing other non-target impacts.

Three amino acid residues bind corn odorants to McinOBP1 in the polyembryonic endoparasitoid of Macrocentrus cingulum Brischke.

Odorant binding proteins (OBPs) play a central role in transporting odorant molecules from the sensillum lymph to olfactory receptors to initiate behavioral responses. In this study, the OBP of Macrocentrus cingulum McinOBP1 was expressed in Escherichia coli and purified by Ni ion affinity chromatography. Real-time PCR experiments indicate that the McinOBP1 is expressed mainly in adult antennae, with expression levels differing by sex. Ligand-binding experiments using N-phenyl-naphthylamine (1-NPN) as a fluorescent probe demonstrated that the McinOBP1 can bind green-leaf volatiles, including aldehydes and terpenoids, but also can bind aliphatic alcohols with good affinity, in the order trans-2-nonenal>cis-3-hexen-1-ol>trans-caryophelle, suggesting a role of McinOBP1 in general odorant chemoreception. We chose those three odorants for further homology modeling and ligand docking based on their binding affinity. The Val58, Leu62 and Glu130 are the key amino acids in the binding pockets that bind with these three odorants. The three mutants, Val58, Leu62 and Glu130, where the valine, leucine and glutamic residues were replaced by alanine, proline and alanine, respectively; showed reduced affinity to these odorants. This information suggests, Val58, Leu62 and Glu130 are involved in the binding of these compounds, possibly through the specific recognition of ligands that forms hydrogen bonds with the ligands functional groups.

Morphology and ultrastructure of antennal sensilla of Macrocentrus cingulum Brischke (Hymenoptera: Braconidae) and their probable functions.

Macrocentrus cingulum Brischke (Hymenoptera: Braconidae) is a polyembryonic endoparasitoid of the Asian corn borer, Ostrinia furnacalis and the European corn borer, Ostrinia nubilalis. To better understand the host location mechanism, we examined the external morphology and ultrastructure of the antennal sensilla of this parasitoid by using scanning and transmission electron microscopy. Antennae of male and female of the M. cingulum are filiform in shape, 5.90-6.64mm in length and consist of scape, pedicel, and flagellum with 39 and 40 flagellomeres, respectively. Cuticular pore and nine types of morphologically distinct sensilla were identified in both sexes, including two types of sensilla chaetica (nonporous), s. trichodea (nonporous), s. basiconica I (nonporous blunt tip), s. basiconica II (porous wall) and basiconica III (nonporous wall) with branched blunt tip, s. coeloconica with finger-like projections, protruded s. campaniform with central tip pore, and plate-like s. placodea (porous). We compared number, morphology, and distribution of sensilla between sexes. S. campaniform and non-porous basiconica type I may play a role in gustatory functions whereas type II, and s. placodea may play a function in detecting odor stimuli due to their pores wall. The sensilla chaetica and s. trichodea may be involved in mechnosensation. S. coeloconica probably plays a role as thermo-hygro receptor, whilst cuticular pores may detect odor stimuli. No differences in antenna shape and basic structure in the males and females, but male antennae length and width were significantly greater than those of females. Furthermore, males had more placodea than females. The sensilla types, morphology, and structure of both sexes were compared to those found in other parasitic hymenoptera, especially braconid wasps.

Characterization of three pheromone-binding proteins (PBPs) of Helicoverpa armigera (Hübner) and their binding properties.

Three pheromone-binding proteins of Helicoverpa armigera were cloned and expressed in Escherichia coli. In order to characterize their physiological properties, ligand-binding experiments were performed using five biologically relevant substances including sex pheromones and interspecific signals. The results showed that one of the pheromone-binding proteins, HarmPBP1, binds strongly to each of the two principal pheromone components of H. armigera, (Z)-11-tetradecenal and (Z)-9-hexadecenal, but not to the interspecific signal (Z)-9-tetracecenal. The two remaining pheromone-binding proteins, HarmPBP2 and HarmPBP3, showed only weak affinities with the ligands tested. The 3-D structure of HarmPBP1 was predicted and the docking experiments indicate that the key binding site of (Z)-9-hexadecenal to HarmPBP1 includes Thr112, Lys111, and Phe119 whereas that of (Z)-11-tetradecenal includes Ser9, Trp37, Phe36, and Phe119.