Insect kinins are endogenous, biologically active peptides with various physiological functions. The use of insect kinins in plant protection is being evaluated by many groups. Some kinins have been chosen as lead compounds for pest control. We previously reported an insect kinin mimic IV-3 that had insecticidal activity. And by introducing a strong electron withdrawing group (-CF3 ) on the benzene ring (Phe2 ), we discovered a compound, L7 , with better activity than lead IV-3. In this work, taking L7 as the lead compound, we designed and synthesized 13 compounds to evaluate the influence of position 4 (Trp4 ) of insect kinin on insecticidal activity, by replacing the H atom on tryptophan with -CH3 and -Cl or substituting the indole ring of tryptophan with the benzene, naphthalene, pyridine, imidazole, cyclohexane, and alkyl carboxamides. The aphid bioassay results showed that the compounds M1 , M3 , and M5 were more active than the positive control, pymetrozine. Especially, replacing the side chain by an indole ring with 4-Cl substitution (M1 , LC50 = 0.0029 mmol/L) increased the aphicidal activity. The structure-activity relationships (SARs) indicated that the side chain benzene ring at this position may be important to the aphicidal activity. In addition, the toxicity prediction by Toxtree, and the toxicity experiments on Apis mellifera suggested that M1 was no toxicity risk on a non-target organism. It could be used as a selective and bee-friendly insecticide to control aphids.
Curzate,a fungicide,is a formulation of cymoxanil and mancozeb.Cymoxanil and metabolite ethylenethiourea(ETU)of mancozeb were determined by HPLC,and miancozeb by GC in the present study.The result showed that the minimum detectable limits were 2.1×10-9 g for Cymoxanil,1.3×10-10 g for mancozeb and 2.5×10-10 g for ETU,respectively.The minimum detectable concentrations were found to be:0.02 mg·kg-1 for lichee skin;0.015 mg·kg-1 for flesh and 0.01 mg·kg-1 for soil,respectively.In terms of cymoxanil,mancozeb and ETU were,respectively,0.025 mg·kg-1 and 0.02 mg·kg-1 for the three kinds of samples.The average recoveries were 84.0%～94.0% for cymoxanil,89.2%～95.9% for mancozeb,89.1%～95.1% for ETU,respectively,fortified in the plant tissues.The coefficients of variation were 0.93～6.67.The half-lives of were 19.2～24 hours in lichee skin and 18～20 hours in the soil.In addition,over 97% had degraded after 21 days the curzate was applied.It has been also found that the highest residues of curzate were in an arrange of 0.365 7～0.373 5 mg·kg-1 in lichee skin,0.421 9～0.483 1 mg·kg-1 in the soil,and untreated in lichee,flesh at harvest time.It may be concluded that in consideration of the MRL(0.5mg·kg-1)of EU,application curzate with dilutions of 250～500 times and spraying 4～5 times of 72% curzate WP over the plant growth will cause little problems for food safety.
Using natural enemies provides a sustainable method to control major agricultural pests. Hoverflies are significant natural enemies of aphids and efficient pollinators. Herbivore-induced plant volatiles (HIPVs), including (E)-β-farnesene (EBF) and methyl salicylate (MeSA), are key olfactory cues mediating hoverflies behavior. Our previous work identified compound 3e, an EBF analog containing a MeSA moiety, exhibited aphid-repelling and ladybug-attracting activities. However, whether 3e can attract hoverflies remains unknown. Therefore, this study explored the attractant property and potential mechanism of 3e toward hoverflies. Laboratory bioassays and field trials indicated 3e has an obvious hoverfly attracting property. The attraction mechanism studies demonstrate that, similar to EBF, 3e can interact with EcorOBP15 and EcorOR3, with its greater chemical softness, larger hydrophobic and charge regions enhancing these interactions. Furthermore, 3e exhibited low toxicity to honeybees (Apis mellifera) and hoverflies (Eupeodes corollae). Consequently, 3e could be a promising eco-friendly behavioral regulator for integrated aphid management in sustainable agriculture.
Bees, one of the most vital pollinators in the ecosystem and agriculture, are currently threatened by neonicotinoids. To explore the molecular mechanisms of neonicotinoid toxicity to bees, the different binding modes of imidacloprid, thiacloprid, and flupyradifurone with nicotinic acetylcholine receptor (nAChR) α1β1 and cytochrome P450 9Q3 (CYP9Q3) were studied using homology modeling and molecular dynamics simulations. These mechanisms provided a basis for the design of compounds with a potential low bee toxicity. Consequently, we designed and synthesized a series of triazinone derivatives and assessed their bioassays. Among them, compound 5a not only displayed substantially insecticidal activities against Aphis glycines (LC50 = 4.40 mg/L) and Myzus persicae (LC50 = 6.44 mg/L) but also had low toxicity to Apis mellifera. Two-electrode voltage clamp recordings further confirmed that compound 5a interacted with the M. persicae nAChR α1 subunit but not with the A. mellifera nAChR α1 subunit. This work provides a paradigm for applying molecular toxic mechanisms to the design of compounds with low bee toxicity, thereby aiding the future rational design of eco-friendly nicotinic insecticides.
A modified quick, easy, cheap, effective, rugged (QuEChERS) method with multi-walled carbon nanotubes (MWCNTs) as reversed-dispersive solid phase extraction (r-DSPE) material was applied to the analysis of pirimiphos-methyl and deltamethrin residues in stored rice. Two dustable powder (DP) formulations (2% pirimiphos-methyl and deltamethrin DP; 5% pirimiphos-methyl DP) were applied in simulated storehouse trials in the lab. The residues and dissipation of the two pesticides in stored rice were investigated. Slow dissipation of both pesticides was observed in stored rice. The half-lives of pirimiphos-methyl were 23.9–28.9 days, and those of deltamethrin were 23.9–24.8 days. Residues of pirimiphos-methyl from application rates of 4.5–6.75 a.i. mg/kg (active ingredient milligram per kilogram) and 10–15 a.i. mg/kg were 1.6–3.8 mg/kg and 3.0–4.5 mg/kg at 60 days Pre-harvest Interval (PHI). Residues of deltamethrin from an application rate of 0.5–0.75 a.i. mg/kg were 0.13–0.14 mg/kg at 60 days PHI. Both pesticides residues were below the Maximum Residue Limits (MRLs) established by the Codex Alimentarius Commission (CAC). Therefore, at the recommended dosages they are safe for use on stored rice.
As with other Lepidoptera species, the fall armyworm (FAW; Spodoptera frugiperda) exhibits extremely strong reproductive ability and pesticide resistance, and juvenile hormone (JH) plays important regulatory roles in both the processes. However, few studies have reported this JH-mediated coordination of reproduction and pesticide resistance in Lepidoptera. Herein, three different JHs and chlorantraniliprole (CH) were separately injected into FAW to characterize their differences in regulating the expression of key reproductive and detoxification enzymes. Furthermore, the molecular docking of the different JHs to their receptor, methoprene-tolerant (Met), was analyzed. The results revealed that JH injected in vitro entered the ovaries to regulate reproduction, whereas JH passively upregulated by CH entered the fat body to regulate resistance. JH I occupied more active cavities on Met, including 18 groups of hydrophobic amino acids and 2 side chain ethyl groups, thereby stabilizing the structure of JH I. Furthermore, JH I exhibited higher bioactivity than JH II and JH III in regulating fertility. These results present a primary assessment of the trade-off between JH-mediated reproduction and resistance and reveal that JHs can manipulate the interactions between reproduction and resistance to establish advantages for FAWs in their natural environment.
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