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Redroot pigweed (Amaranthus retroflexus L.) is a dominant weed in soybean [Glycine max (L.) Merr.] fields in Heilongjiang Province, China. High selective pressure caused by the extensive application of the protoporphyrinogen oxidase (PPO)-inhibiting herbicide fomesafen has caused A. retroflexus to evolve resistance to this herbicide. Two susceptible and two resistant populations (S1, S2, R1, and R2) were selected in this study to illustrate the target-site resistance mechanism in resistant A. retroflexus. Whole-plant bioassays indicated that R1 and R2 had evolved high-level resistance to fomesafen, with resistance factors of 27.0 to 27.9. Sequence alignment of the PPO gene showed an Arg-128-Gly substitution in PPX2. The basal expression differences of PPX1 and PPX2 between the S1 and R1 plants were essentially nonsignificant, whereas the basal expression of PPX2 in R2 plants was slightly lower than in S1 plants. Compared with the PPX1 gene, the PPX2 gene maintained higher expression in the resistant plants after treatment with fomesafen. An enzyme-linked immunosorbent assay showed a similar basal PPO content between the susceptible and resistant plants without treatment. After fomesafen treatment, the PPO content decreased sharply in the susceptible plants compared with the resistant plants. Furthermore, after 24 h of treatment, the resistant plants showed increased PPO content, whereas the susceptible plants had died. The PPO2 mutation resulted in high extractable PPO activity and low sensitivity to fomesafen along with changes in PPO enzyme kinetics. Although the mutant PPO2 exhibited increased Km values in the resistant plants, the Vmax values in these plants were also increased. Changes in the properties of the PPO enzyme due to an Arg-128-Gly substitution in PPX2, including changes in enzyme sensitivity and enzyme kinetics, are the target-site mechanism of resistance in A. retroflexus.

Peanut is one of the most important oilseed crop grown in China. Purple nutsedge (Cyperus rotundus L.) is a competitive perennial weed, which infests peanut fields in south China and causes considerable peanut yield losses. Information on the interference of purple nutsedge on peanut and its economic threshold (ET) in field is an integral component of integrated weed management system. This will help growers use herbicides more legitimately and reduce the amount of herbicide that is discharged into the environment. 2-year experiments were conducted to assess the infestation effects of purple nutsedge on peanut in pure stands (nutsedge density 0, 5, 10, 20, 40, 80, 120 and 160 plants m−2) and in natural weed infestation, respectively. Furthermore, the ET of purple nutsedge in peanut was determined according the quadratic equation reported by Cousens. The biomass of purple nutsedge with a density of 160 plants m−2 in pure stand was less than that of natural weed infestation treatment. Compared with natural weed infestation treatments, lower yield loss in treatment of nutsedge 160 plants m−2 indicated weaker interference on peanut. But the ET of purple nutsedge in peanut came down to 4–5 plants m−2. The higher price of peanut than the cost of weed control and very high efficiency (90%) of imazapic could be the probable reasons.

Weed resistance to herbicide can be conferred by gene mutations, and some mutations can cause pleiotropic effects in some cases. We investigated the pleiotropic effects associated with five specific ACCase mutations (Ile1781Leu, Trp2027Cys, Ile2041Asn, Asp2078Gly, and Gly2096Ala) on the plant growth, seed production, and resource competitiveness in American sloughgrass.Resistant plants (M/M) homozygous for specific ACCase mutation and susceptible wild‐type plants (W/W) were derived from single heterozygous mother plant (M/W) by genotyping. Plant growth assay and neighborhood experiments were performed to quantify variation between M/M plants and W/W plants.The Ile1781Leu mutation resulted in slight increases in plant growth in pure stands and improved resource competitiveness under low‐competition conditions in pot experiments, but no clear variation was observed under high competitive pressure or field conditions. During competition with wheat plants under field conditions, American sloughgrass plants containing Ile2041Asn ACCase exhibited a significantly lower (12.5%) aboveground biomass but no distinct differences in seed production or resource competitiveness. No significant detrimental pleiotropic effects associated with Gly2096Ala were detected in American sloughgrass.The Trp2027Cys mutation distinctly reduced seed production, especially under high competitive pressure, but did not significantly alter plant growth. The Asp2078Gly mutation consistently reduced not only plant growth and seed production but also resource competitiveness. Synthesis. The Trp2027Cys and Asp2078Gly mutations led to significant fitness costs, which may reduce the frequency of resistance alleles and reduce the propagation speed of resistant weeds in the absence of ACCase inhibitor herbicides. The Ile1781Leu, Ile2041Asn, and Gly2096Ala mutations displayed no obvious fitness costs or displayed very small fitness penalties, which would likely have no effect on the establishment of resistant weeds in the field.

To clarify feasibility of using combinations of imazapic and prometryn to control weeds in peanut field, their interaction effect was evaluated in greenhouse and verified in field. The results of pot experiments showed that the interaction of imazapic at 32 g a.i. ha−1 and prometryn at 400–850 g a.i. ha−1 exhibited synergistic effects for the control of Chenopodium album L., Portulaca oleracea L. and Digitaria sanguinalis (L.) Scop., and that the observed response (E0) was significantly greater than that expected (E). The combination of imazapic at 52 g a.i. ha−1 and prometryn at 400–850 g a.i. ha−1 also had synergistic effects on the control of Echinochloa crus-galli (L.) Beauv., and the E0 value was significantly greater than the E value. Field experiment demonstrated that imazapic plus prometryn at 32 + 850 g a.i. ha-1 or 52 + 400 g a.i. ha-1 exhibited better weed density suppression (93.2% or 95.1%), which was significantly higher than imazapic (85.0%) and prometryn (71.8%) applied at 90 g a.i. ha−1 and 950 g a.i. ha−1, respectively. The combinations showed superior weed fresh weight control than when they were applied alone. Comparing with s-metolachlor, the mixtures also provided significantly higher control of weed density and fresh weight under field condition. The mixtures were safe for peanut. These findings indicate that PRE application of combinations of imazapic and prometryn has great potential for weed control in peanut fields in China and that recommended field doses of imazapic plus prometryn are 32 + 850 or 52 + 400 g a.i. ha−1.

The dark black chafer (DBC), Holotrichia parallela, is an important pest of multiple crops. Insect host-searching behaviors are regulated by host plant volatiles. Therefore, a better understanding of the mechanism linking the chemosensory system to plant volatiles at the molecular level will benefit DBC control strategies. Based on antenna transcriptome data, two highly expressed antenna-specific odorant-binding proteins (HparOBP20 and 49) were selected to identify novel DBC attractants using reverse chemical ecology methods. We expressed these proteins, mapped their binding specificity, and tested the activity of the plant volatiles in the field. The ligands used in the binding specificity assays included 31 host-plant-associated volatiles and two sex pheromone components. The results showed that (1) HparOBP20 and 49 are involved in odor recognition; (2) these proteins bind attractive plant volatiles strongly and can therefore be employed to develop environmentally friendly DBC management strategies; and (3) the green-leaf volatile (Z)-3-hexenyl acetate shows a high binding affinity to HparOBP20 (Ki = 18.51 μM) and HparOBP49 (Ki = 39.65 μM) and is highly attractive to DBC adults, especially females. In the field test, a (Z)-3-hexenyl acetate trap caught an average of 13 ± 1.202 females per day, which was significantly greater than the corresponding male catch (F2,6 = 74.18, P < 0.0001). (Z)-3-Hexenyl acetate may represent a useful supplement to the known sex pheromone for DBC attraction. In the present study, the binding characteristics of two HparOBPs with host plant volatiles were screened, providing behaviourally active compounds that might be useful for DBC control, based on reverse chemical ecology.

The dark black chafer, Holotrichia parallela, is an economically important pest in China and worldwide. Traps based on chemical communication are being developed as an alternative control measure to pesticides for this pest, and studies to reveal chemical communication mechanisms in this pest are highly desirable. To systematically analyze genes potentially involved in chemical communication in this pest, we generated a comprehensive transcriptome with combined samples derived from multiple tissues and developmental stages. A total of 43,967 nonredundant sequences (unigenes) with average length of 806 bp were obtained. These unigenes were annotated into different pathways using gene ontology analysis and cluster analysis of orthologous groups of proteins, and kyoto encyclopedia of genes and genomes. In total, 25 transcripts encoding odorant-binding proteins (OBPs) and 16 transcripts encoding chemosensory proteins (CSPs) were identified based on homology searches. Tissue-specific expression profile indicates that OBP17 and CSP7 are likely responsible for male sex pheromone recognition, whereas OBP1-4, OBP9, OBP13-14, OBP17-18, OBP20, OBP22, OBP25, CSP1-7, CSP11, and CSP12-15 are likely responsible for chemical communication between the beetle and environments. Our data shall provide a foundation for further research on the molecular aspects of chemical communication of this insect, and for comparative genomic studies with other species.

The dark black chafer, Holotrichia parallela Motschulsky, is an economically important pest worldwide. Odorant-based lures and traps are being developed as a key kind of alternative control measures for this pest, and studies to reveal the mechanisms for chemotaxis in this pest are necessary. Two full-length cDNAs encoding different odorant-binding proteins (OBPs) were cloned. The predicted proteins were found to have the functional domains characteristic of typical OBPs and share a high degree of sequence similarity with OBP1 and OBP2 from other insects and were therefore designated as H. parallela OBP-1 and H. parallela OBP-2 (HparOBP-1 and HparOBP-2, respectively). These two OBPs were specifically expressed in antennae. The binding affinity of two purified proteins indicated that HparOBP-1 and HparOBP-2 could selectively interact with various volatiles emitted from host plants and pheromone components. Among the 10 chemicals tested, HparOBP-1 could bind to six of the tested compounds with a dissociation concentration (Ki) less than 20, and HparOBP-2 could bind to three of the compounds. The two OBPs are probably involved in chemotaxis of the dark black chafer. This discovery should accelerate research on chemical communications of this pest, which could potentially lead to the improvement of control measures based on lures and traps.

Two full-length genes encoding different acetylcholinesterases (AChEs), designated as Ch-ace1 and Ch-ace2, were cloned from strains of the rice stem borer (Chilo suppressalis) susceptible and resistant to the organophosphate insecticide triazophos. Sequence analysis found an amino acid mutation A314S in Ch-ace1 (corresponding to A201 in Torpedo californica AChE) that was consistently associated with the occurrence of resistance. This mutation removed an MspA1 I restriction site from the wild type allele. An assay based on restriction fragment length polymorphism (RFLP) analysis was developed to diagnose A314S genotypes in field populations. Results showed a strong correlation between frequencies of the mutation and phenotypic levels of resistance to triazophos. The assay offers a prospect for rapid monitoring of resistance and assisting with the appropriate choice of insecticide for combating damage caused by C. suppressalis.

Holotrichia parallela (Coleoptera: Scarabaeoidea) is a notorious pest of many crops. To improve the effectiveness of its female-produced sex pheromone (L-isoleucine methyl ester:(R)-(−)-linalool = 6:1), 14 plant volatiles, including dodecanoic acid, dodecanal, farnesol, α-farnesene, (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol, (Z)-3-hexenyl acetate, (E)-2-hexenyl acetate, (R)-(+)-limonene, α-phellandrene, α-pinene, ocimene, methyl benzoate, and benzaldehyde, were individually evaluated using electroantennography and olfactometer assays. (E)-2-Hexenyl acetate and (Z)-3-hexenyl acetate were found to elicit the strongest responses in both males and females. Further testing of these two compounds in mixtures with the sex pheromone indicated that (E)-2-hexenyl acetate had a stronger synergistic effect than (Z)-3-hexenyl acetate. Field evaluations showed that mixtures of (E)-2-hexenyl acetate and the sex pheromone resulted in significantly higher catches than the sex pheromone alone. Using a 5:1 mixture of the sex pheromone and (E)-2-hexenyl acetate, the maximum number of females per trap per day was 14, showing a synergistic effect of a factor of four. For males, a 3:1 mixture of the sex pheromone and (E)-2-hexenyl acetate yielded a maximum number of 310 individuals per trap per day, equivalent to a synergistic effect of 175%. These results may provide the basis for the development of efficient pest management systems against H. parallela using plant volatiles and insect sex pheromones.

Background The metallic green beetle, Anomala corpulenta (Coleoptera: Scarabaeidae: Rutelinae), is a destructive pest in agriculture and horticulture throughout Asia, including China. Olfaction plays a crucial role in the survival and reproduction of A. corpulenta. As a non-model species, A. corpulenta is poorly understood, and information regarding the molecular mechanisms underlying olfaction in A. corpulenta and other scarab species is scant. Methodology/Principle Findings We assembled separate antennal transcriptome for male and female A. corpulenta using Illumina sequencing technology. The relative abundance of transcripts with gene ontology annotations, including those related to olfaction in males and females was highly similar. Transcripts encoding 15 putative odorant binding proteins, five chemosensory proteins, one sensory neuron membrane protein, 43 odorant receptors, eight gustatory receptors, and five ionotropic receptors were identified. The sequences of all of these chemosensory-related transcripts were confirmed using reverse transcription polymerase chain reaction (RT-PCR), and direct DNA sequencing. The expression patterns of 54 putative chemosensory genes were analyzed using quantitative real time RT-PCR (qRT-PCR). Antenna-specific expression was detected for many of these genes, suggesting that they may have important functions in semiochemical detection. Conclusions The identification of a large number of chemosensory proteins provides a major resource for the study of the molecular mechanism of odorant detection in A. corpulenta and its chemical ecology. The genes identified, especially those that were expressed at high levels in the antennae may represent novel molecular targets for the development of population control strategies based on the manipulation of chemoreception-driven behaviors.

A field population of the rice stem borer (Chilo suppressalis Walker) with 203.3-fold resistance to triazophos was collected. After 8-generation of continuous selection with triazophos in laboratory, resistance increased to 787.2-fold, and at the same time, the resistance to isocarbophos and methamidophos was also enhanced by 1.9- and 1.4-fold, respectively, implying some cross-resistance between triazophos and these two organophosphate insecticides. Resistance to abamectin was slightly enhanced by triazophos selection, and fipronil and methomyl decreased. Synergism experiments in vivo with TPP, PBO, and DEM were performed to gain a potential indication of roles of detoxicating enzymes in triazophos resistance. The synergism results revealed that TPP (SR, 1.92) and PBO (SR 1.63) had significant synergistic effects on triazophos in resistant rice borers. While DEM (SR 0.83) showed no effects. Assays of enzyme activity in vitro demonstrated that the resistant strain had higher activity of esterase and microsomal O-demethylase than the susceptible strain (1.20- and 1.30-fold, respectively). For glutathione S-transferase activity, no difference was found between the resistant and the susceptible strain when DCNB was used as substrate. However, 1.28-fold higher activity was observed in the resistant strain when CDNB was used. These results showed that esterase and microsomal-O-demethylase play some roles in the resistance. Some iso-enzyme of glutathione S-transferase may involve in the resistance to other insecticides, for this resistant strain was selected from a field population with multiple resistance background. Acetylcholinesterase as the triazophos target was also compared. The results revealed significant differences between the resistant and susceptible strain. The Vmax and Km of the enzyme in resistant strain was only 32 and 65% that in the susceptible strain, respectively. Inhibition tests in vitro showed that I50 of triazophos on AChE of the resistant strain was 2.52-fold higher. Therefore, insensitive AChE may also involved in triazophos resistance mechanism of rice stem borer.