Potent Acaricidal Activity Research Articles

Screening of volatile compounds of essential oils with acaricidal activity in Rhipicephalus microplus larvae using a new in vitro evaluation method

ABSTRACT The study assessed the acaricidal properties of 20 compounds derived from essential oils against the Rhipicephalus microplus tick, a significant menace to tropical livestock with considerable economic losses. A novel methodology was devised, involving the determination of mortality times for R. microplus larvae upon direct contact with these compounds. Mortality times were compared against a negative control (soybean oil) and two positive controls (commercial pour-on products). Tests were conducted in 48-well polyethylene plates, with around 100 larvae immersed in 200 µl of oil (at a 100% dose). The 10 compounds exhibiting the shortest mortality times were subsequently diluted in soybean oil at varying concentrations. Notably, thymol exhibited potent acaricidal activity, with the lowest effective dose (1.56%) resulting in larval mortality within 15 minutes, whereas positive controls necessitated over 66 minutes. A correlation was established between the molecular structure of the compounds and their acaricidal efficacy, indicating that cyclic compounds containing 10 carbon atoms demonstrated heightened lethality compared to acyclic counterparts. This innovative methodology enables the rapid identification of substances with substantial acaricidal potential in vitro, yielding results within minutes, in stark contrast to the traditional larval immersion test, which demands a minimum of 24 hours for conclusive outcomes.

Acaricidal activity of methanolic extract of leaves of Cleistanthuscollinus(Roxb.) Benth. Ex Hook.f

Ticks are parasitic haematophagus arthropods playing a major role in disease transmission among human and animals. Effective tick control is mainly accomplished through widespread use of chemical acaricides, which have a negative impact on environment, humans, and animals due to their toxicity and indiscriminate use leads to resistance developement. So, there arise an essentiality for development of safer, eco-friendly methods for control of acarine parasites. The present study was conducted to identify phytochemicals in methanolic extract of leaves of Cleistanthus collinus. and its acaricidal activity against Haemophysalis bispinosa. Leaves of C. collinus were harvested at the College of Veterinary and Animal Sciences Mannuthy campus in Thrissur, Kerala, India. They were shade-dried, ground into a powder, and extracted using methanol. A rotary vacuum evaporator was used to concentrate extract, and FTIR, GCMS, and qualitative phytochemical screening were carried out. Acaricidal activity was determined by adult immersion assay by accounting for various entomological parameters such as per cent adult mortality, index of egg laying and percent inhibition of fecundity using various concentrations of extract. Phytochemical analysis detected presence of steroids, alkaloids, glycosoides, flavonoids, terpenoids, in methanolic extract of C.collinus leaves. GC–MS analysis confided presence of Dianhydromannitol,Diethyl phthalate, Cyclooctasiloxane, Benzophenone, Dodecanoic acid, Tetradecanoicacid, Hexadecenoic acid, among many compounds. FTIR analysis ascertained presence of various functional groups like aldehydes, sulfoxides, phenol, vinyl ether and aliphatic ketones. There was cent per cent mortality of ticks in all doses tested. Index of egg laying was found to be zero and maximum inhibition of fecundity was observed in higher concentrations. IC50 found to be 30.84 mg/mL. From results, it was clear that methanolic extract of leaves of C.collinus induced very early adult tick mortality. It was apparent that methanolic extract of C.collinus leaves flaunted potent acaricidal activity against H. bispinosa and can be used to develop a potent ectoparasiticide.

Acaricidal activities of paeonol from Moutan Cortex, dried bark of Paeonia × suffruticosa, against the grain pest mite Aleuroglyphus ovatus (Acari: Acaridae).

Aleuroglyphus ovatus (Acari: Acaridae) is a major pest mite of stored grains that is distributed worldwide. Paeonol, a phenolic component of the essential oil extracted from the Chinese herb Paeonia moutan, possesses a range of biological activities, including antiviral, antifungal and acaricidal activity. This study investigated the bioactivity of paeonol against A. ovatus and its effect on the activity of detoxification enzymes. The bioactivity of paeonol against A. ovatus was determined by contact, fumigation and repellency bioassays, and the mechanism was preliminarily explored via morphological observation of the color changes of mite epidermis and determination of the changing trend of some important enzymes associated with acaricidal efficacy in the mites. The results showed that the median lethal concentration (LC50) in the contact and fumigation bioassays was 9.832μg/cm2 and 14.827μg/cm3, respectively, and the acaricidal activity of paeonol was higher under direct contact than under fumigation. Dynamic symptomatology studies registered typical neurotoxicity symptoms including excitation, convulsion and paralysis in A. ovatus treated with paeonol. The enzyme activity of catalase (CAT), nitric oxide synthase (NOS) and glutathione-S-transferase (GST) was higher, whereas the activity of superoxide dismutase (SOD) and acetylcholinesterase (AChE) was lower, compared to the control group. CAT, NOS and GST were activated, whereas SOD and AChE activities were inhibited after paeonol intervention. Our findings suggest paeonol has potent acaricidal activity against A. ovatus and thus may be used as an agent to control the stored-product mite A. ovatus.

Syntheses of (+)-costic acid and structurally related eudesmane sesquiterpenoids and their biological evaluations as acaricidal agents against Varroa destructor.

Synthesis of (+)-costic acid, isolated from Dittrichia viscosa (L.) W. Greuter as a natural acaricidal sesquiterpenoid, was achieved in 16 steps from (R)-carvone with an overall yield of 4.8%, involving the radical cyclization of selenoester to construct a decalone framework as the key step. Other structurally related natural products, (+)-costal, (+)-costol, and (+)-β-selinene, were also synthesized. The acaricidal activities of these four natural products and some synthetic intermediates were also evaluated against Varroa destructor. Among them, (+)-costal especially exhibited potent acaricidal activity.

Construction and agrochemical efficacy of novel indolo[2,3-b]andrographolide derivatives

To find new pesticide candidates, by using of a natural product andrographolide as the precursor, a series of novel indolo[2,3-b]andrographolide derivatives were semisynthesized by Fischer-indole rearrangement reaction. Their structures were identified by 1H NMR, IR, mp, and HRMS, and the steric configuration of compound Ic was further determined on single-crystal analysis. Compounds If and IIb showed 5.9 and 7.0 times potent acaricidal activity compared to andrographolide against Tetranychus cinnabarinus. Compound Ib displayed 4.2 folds higher aphicidal activity compared to andrographolide against Eriosoma lanigerum. In addition, the pronounced insecticidal activity of compound IIc against Aphis citricola was 4.2 folds of that of andrographolide. Scanning electron microscopy revealed that compound IIb can destroy the epidermis of T. cinnabarinus. These results can provide a basis for future research on botanical agrochemicals.

Green synthesis, characterization, acaricidal, larvacidal, and repellent activities of copper nanoparticles of Astragalus sinicus against Hyalomma anatolicum

Objective: To green synthesize and characterize copper nanoparticles (CuNPs) using Astragalus sinicus, as well as evaluate the acaricidal, larvacidal, and repellent activities of CuNPs against Hyalomma anatolicum (H. anatolicum), one of the most prevalent ticks infesting cattle in Saudi Arabia. Methods: CuNPs were green synthesized by adding the Astragalus sinicus extract to a copper sulfate solution. The acaricidal, larvicidal, and repellent activities of CuNPs against H. anatolicum were assessed via the adult immersion test, the larval packet test, and the vertical movement behavior of tick larvae, respectively. The effects of CuNPs on acetylcholinesterase as well as oxidative enzyme activities were examined. Results: The green synthesized CuNPs displayed a spherical form with a size range of 15-75 nm. After exposure of adult H. anatolicum to different concentrations of CuNPs, the viability rate of adult H. anatolicum and the mean number, weight, and hatchability of eggs were noticeably reduced, in comparison to the control group (P<0.001). In addition, the viability rate of larvae considerably declined (P<0.001) with the LC50 and LC90 values of 11.30 and 20.34 μg/mL, respectively. The maximum repellent activity of CuNPs was observed at 50, 100, and 200 μg/mL with complete repellent activity after 60, 120, and 180 min of exposure, respectively. CuNPs, mainly at ½LC50 and LC50 concentrations, markedly suppressed the acetylcholinesterase activity of the larval stage of H. anatolicum (P<0.001). Moreover, CuNPs, mainly at LC50 dose, significantly elevated malondialdehyde level while declining glutathione-S-transferase level in H. anatolicum larvae (P<0.001). Conclusions: CuNPs show potent acaricidal, larvicidal, and repellent activities against adults and larvae of H. anatolicum. However, further studies must be performed to clarify the precise mechanisms and the efficacy of CuNPs in practical use.

Target identification and acaricidal activity difference of amitraz and its metabolite DPMF in Tetranychus cinnabarinus (Boisduval).

Amitraz is a broad-spectrum formamidine acaricide proven to be effective against mites in all development stages. Under acidic conditions, amitraz is hydrolyzed to N2 -(2,4-dimethylphenyl)-N1 -methyformamidine (DPMF), an active metabolite for mite control. Octopamine and tyramine receptors are well known targets of amitraz. Until now, no research has been conducted about the amitraz target in Tetranychus cinnabarinus. This study aimed to identify the target genes of amitraz in T. cinnabarinus and reveal the mechanisms behind the differential acaricidal activities of amitraz and DPMF. Analysis of the toxicity, stress expression, target sensitivity and binding site of amitraz against T. cinnabarinus showed that TcOctβ2R was the main target gene of amitraz. DPMF had more potent acaricidal activity against T. cinnabarinus and was more effective at activating TcOctβ2R than amitraz. Furthermore, the three synergists had no significant effect on amitraz and DPMF, indicating that the detoxification metabolism was not related to the difference in acaricidal activity. In this study, TcOctβ2R was identified as the main target gene of amitraz against T. cinnabarinus. The divergence of target binding was responsible for the difference in acaricidal activity between amitraz and DPMF. The results also revealed the physiological and pharmacological functions of octopamine receptors (OARs) in T. cinnabarinus and could provide a basis for the design of new acaricides, with OARs as a special target. © 2023 Society of Chemical Industry.

High Value-Added Application of Natural Products in Crop Protection: Semisynthesis and Acaricidal Activity of Limonoid-Type Derivatives and Investigation of Their Biocompatible O/W Nanoemulsions as Agronanopesticide Candidates.

The increasingly serious resistance of Tetranychus cinnabarinus Boisduval to a wide range of insecticides/acaricides poses a major challenge to their control. The citrus processing industry generates a huge quantity of various wastes that contain many limonoids. To effectively utilize these byproducts and discover more potent green acaricidal molecules as sustainable alternatives for traditional resistant pesticides, various limonoid-type derivatives (halogenated/seven-membered lactam derivatives of obacunone and halogenated/oxime esters/oxime ethers/seven-membered lactam derivatives of limonin) were synthesized based on a diversity-oriented synthetic strategy. The key steric configurations of 10 derivatives were further confirmed by X-ray crystallography. Compound 9m, which displayed greater than 9.7-fold potent acaricidal activity of limonin, was of preeminence. In addition, some interesting structure-activity relationships were observed. Moreover, a biocompatible O/W nanoemulsion delivery system was used to prepare the limonin-based agronanoacaricide, which exhibited pronounced control efficiency against T. cinnabarinus Boisduval in the greenhouse. This systematic investigation will provide valuable information and guidance for future value-added applications of novel eco-friendly natural product-based nanopesticides.

Determination of Avermectins Residues in Soybean, Bean, and Maize Using a QuEChERS-Based Method and Ultra-High-Performance Liquid Chromatography Coupled to Tandem Mass Spectrometry

Soybean, maize, and bean are crops of great economic importance, but in recent years have suffered with infestations of the caterpillar Helicoverpa armigera, with the main reason being the resistance of this pest to most pesticides. Avermectin emamectin benzoate was recently released to control this pest. Other avermectins, like abamectin, doramectin, eprinomectin, and ivermectin are used in large scale because they potent acaricidal, anthelmintic, and insecticidal activities. Thus, a simple and fast method for the determination of avermectins in these crops based on a quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction procedure and ultra-high performance liquid chromatography with tandem mass spectrometry (UHPLC-MS/MS) analysis was developed and validated. For extraction, water followed by acetonitrile:isopropanol and a partition step with salts was stablished. With the clean-up step using activated EMR-Lipid, limits of detection of 1.2 μg kg−1 for abamectin, doramectin, emamectin benzoate, and ivermectin, and of 2.4 μg kg−1 for eprinomectin were achieved. The validation showed satisfactory results and the method was successfully applied to commercial samples, indicating that it is suitable for routine analysis.

High value-added application of a renewable bioresource as acaricide: Investigation the mechanism of action of scoparone against Tetranychus cinnabarinus

IntroductionInvestigation into the action mechanisms of plant secondary metabolites against pests is a vital strategy for the development of novel promising biopesticides. Scoparone (isolated from Artemisia capillaris), a renewable plant-derived bioresource, displays potent acaricidal activities against mites, but its targets of action remain unclear. ObjectivesThis study aimed to systematically explore the potential molecular targets of scoparone against Tetranychus cinnabarinus and provide insights to guide the future application of scoparone as an agent for the management of agricultural mite pests worldwide. MethodsThe mechanism and potential targets of scoparone against mites were investigated using RNA-seq analysis; RNA interference (RNAi) assays; bioassays; and [Ca2+]i, pull-down and electrophysiological recording assays. ResultsRNA-seq analysis identified Ca2+ signalling pathway genes, specifically 5 calmodulin (CaM1–5) genes and 1 each of L-, T-, N-type voltage-gated Ca2+ channel (VGCC) genes, as candidate target genes for scoparone against mites. Furthermore, RNAi and electrophysiological data showed that the CaM1- and L-VGCC-mediated Ca2+ signalling pathways were activated by scoparone. Interestingly, by promoting the interaction between CaM1 and the IQ motif (a consensus CaM-binding domain of L-VGCC), CaM1 markedly enhanced the activating effect of scoparone on L-VGCC. Pull-down assays further demonstrated that CaM interacted with the IQ motif, triggering L-VGCC opening. Importantly, mutation of the IQ motif significantly weakened CaM1 binding and eliminated the CaM1-mediated enhancement of scoparone-induced L-VGCC activation, indicating that the effect of scoparone was dependent on the CaM1–IQ interaction. ConclusionThis study demonstrates, for the first time, that the acaricidal compound scoparone targets the interface between CaM1 and L-VGCC and activates the CaM-binding site, located in the IQ motif at the L-VGCC C-terminus. This work may contribute to the development of target-specific green acaricidal compounds based on L-VGCC.

Possible acaricidal activity of Jatropha curcas and Ricinus communis seed oils on Alcea rosea

Field evaluation for the acaricidal activity of jatropha Jatropha curcas and castor bean oils Ricinus communis against the nymph and adult stages of the two-spotted spider mite, Tetranychus urticae on Alcea rosea L. were studied. The field trial was conducted out in May 2016 on A. rosea in the experimental farm of Faculty of Agriculture, Suez Canal University, Ismailia, Egypt. The fatty acids constituents of the two essential oils were identified by gas chromatography (GLC) analysis. The acaricidal activity of castor bean oil was recorded higher than that of jatropha oil where the total population reduction rate of jatropha oil was 74.12% for adults while it was 75.19 % for nymphs. Whereas, total population reduction rate of castor bean oil was 77.32% for adults while it was 82.91% for nymphs on A. rosea leaves. Regarding the flowers, the total population reduction rate of jatropha oil was 68.74 % for adults while it was 73.94 % for nymphs but population reduction rate of castor bean oil was 72.33% for adults while it was 76.02% for nymphs. The major constituents of fatty acids identified by using GLC analysis in jatropha and castor bean oils were erucic (44.34%) and ricinoleic acid (41.75%), respectively. The results of this study revealed that the essential oil of J. curcas and R. communis exhibited potent acaricidal activity against T. urticae which may be attributed to the presence of different bioactive compounds which may affect alone or in synergism.

Two New 5-Oxomilbemycins Possessing an Unusual 3,27-Epoxy Bond from the Genetically Engineered Strain Streptomyces bingchenggensis BCJ60

Two undescribed milbemycin derivatives, milbemycin P (1) and milbemycin Q (2), were isolated from a culture of the genetically engineered strain Streptomyces bingchenggensis BCJ60. Their structures were elucidated through the interpretation of NMR and HR-ESI-MS spectroscopic data, as well as comparison with previous reports. Their acaricidal and nematocidal activities against Tetranychus cinnabarinus and Bursaphelenchus xylophilus were tested. The results showed that compounds 1–2 possessed potent acaricidal and nematocidal activities.

Spirodiclofen ether derivatives: semisynthesis, structural elucidation, and pesticidal activities against Tetranychus cinnabarinus Boisduval, Aphis citricola Van der Goot and Mythimna separata Walker.

Spirodiclofen is a spirocyclic tetronic acid-type acaricidal agent. Nowadays, serious pests resistance to spirodiclofen and cross-resistance to other acaricides has appeared. To overcome pests resistance and discover new potential agrochemicals, a series of ether derivatives were prepared based on spirodiclofen as a lead compound. Their pesticidal activities were investigated against three typically agricultural pests, Mythimna separata Walker, Aphis citricola Van der Goot and Tetranychus cinnabarinus Boisduval. Four steric structures of compounds 5e, 5f, 5i and 5j were determined by single-crystal X-ray diffraction. Against T. cinnabarinus, compounds 5b, 5f and 5l exhibited potent acaricidal activity, and their good control effects in the glasshouse were observed when compared with spirodiclofen, especially the control efficiency of compound 5b was comparable to that of spirodiclofen; against M. separata, compound 5j showed > 1.8-fold potent insecticidal activity of spirodiclofen; against A. citricola, compounds 5d and 5j displayed > 2.0-fold potent aphicidal activity of spirodiclofen. The relationships between their structures and agricultural activities were also discussed. Compounds 5b and 5d could be further studied as acaricidal and aphicidal agents, respectively; compound 5j can be considered as a lead compound for the insecticidal and aphicidal activities. This will pave the way for future application of these derivatives as pesticide substitutes for spirodiclofen. © 2021 Society of Chemical Industry.

Construction of oxime ester derivatives of osthole from Cnidium monnieri, and evaluation of their agricultural activities and control efficiency.

In order to discover natural-product-based pesticidal candidates, a series of coumarin-like derivatives containing oxime ester fragments at the C-8 position were prepared by structural modification of osthole, a natural plant product isolated from Cnidium monnieri. Their pesticidal activities were evaluated against two typically fruit trees/crop-threatening agricultural pests, Mythimna separata Walker and Tetranychus cinnabarinus Boisduval. Osthole was regioselectively oxidized by selenium dioxide to give the E-isomer, (2'E)-3'-formaldehydylosthole (2). Four key steric structures of 2, (2'E, 4'E)-(o-chloropyrid-3-ylcarbonyl)oximinylosthole (4o), (2'E, 4'E)-(styrylcarbonyl)oximinylosthole (4t), and (2'E, 4'E)-(acetyl)oximinylosthole (4w) were undoubtedly confirmed by X-ray crystallography. Against T. cinnabarinus, it is noteworthy that (2'E, 4'E)-(p-chlorophenylcarbonyl)oximinylosthole (4c) exhibited over three-fold more potent acaricidal activity of the precursor osthole, with especially good control efficiency observed in the glasshouse. Against M. separata, compounds 4c and (2'E, 4'E)-(p-nitrophenylcarbonyl)oximinylosthole (4f) showed the most pronounced growth inhibitory activity. The relationships between their structures and agricultural activities also were studied. These results demonstrate that compound 4c could be further structurally modified as pesticidal agents. It will lay the foundation for future application of osthole derivatives as pesticides. © 2020 Society of Chemical Industry.

Two new 13-hydroxylated milbemycin metabolites from the genetically engineered strain Streptomyces avermitilis AVE-H39

Two new milbemycin metabolites, 13α-hydroxymilbemycin β 13 (1) and 26-methyl-13α-hydroxymilbemycin β 13 (2), were isolated from the fermentation broth of a genetically engineered strain Streptomyces avermitilis AVE-H39. Their structures were determined by the comprehensive spectroscopic data, including 1 D, 2 D NMR, MS spectral analysis and the comparison with data from the literature. Compounds 1 and 2 not only exhibited potent acaricidal activities against Tetranychus cinnabarinus, but also had nematocidal activity against Bursaphelenchus xylophilus.

Two new milbemycin derivatives from a genetically engineered strain Streptomyces bingchenggensis

Two new milbemycin derivatives, milbemycin M (1) and milbemycin N (2), were isolated from the culture of a genetically engineered strain Streptomyces bingchenggensis BCJ60. Their structures were elucidated through the interpretation of NMR and HR-ESI-MS spectroscopic data, as well as comparison with previous reports. The acaricidal and nematicidal activities of them against Tetranychus cinnabarinus and Bursaphelenchus xylophilus were tested. The results showed that compounds 1–2 possessed potent acaricidal and nematocidal activities.

Two new sixteen-membered macrolides from the genetically engineered strain Streptomyces avermitilis MHJ1011

Two new sixteen-membered macrolides, Δ2,3-tenvermectin A (1) and 13α-hydroxy milbemycin β11 (2), were isolated from the fermentation broth of the genetically engineered strain Streptomyces avermitilis MHJ1011. Their structures were determined based on extensive spectroscopic analysis and comparison with related known compounds. Compounds 1 and 2 exhibited potent acaricidal activity against Tetranychus cinnabarinus.

Development of essential oil-based phyto-formulations to control the cattle tick Rhipicephalus microplus using a mixture design approach

The cattle tick Rhipicephalus (Boophilus) microplus is one of the most important ectoparasites for livestock in tropical and subtropical areas around the world. This tick economically impacts cattle production by reducing weight gain and milk production. Moreover, it is a vector of pathogens causing diseases such as babesiosis and anaplasmosis. Conventional tick control relies mainly on the use of chemical acaricides; however, their intensive use has led to the rapid appearance of resistant tick populations. It is therefore necessary to look for alternative tick control products. In that sense, plant extracts might represent a promising source of new acaricides. Previously, we reported a significant acaricide effect of essential oils from selected plant species. In the present study, we used a mixture design approach to develop phyto-formulations by combining individual essential oils. We produced several mixtures at 10% containing different proportions of individual essential oils (ranging from 0 to 1) from cinnamon (Cinnamomum zeylanicum), cumin (Cuminum cyminum) and allspice (Pimenta dioica) and tested their acaricidal activity against R. microplus ticks by means of larval packet test (LPT) and adult immersion test (AIT) assays. The optimal mixture predicted against R. microplus was composed of 66%, 17% and 17% of essential oils from C. zeylanicum, C. cyminum and P. dioica, respectively. We generated an estimated response surface contour plot that estimates 80%–100% acaricidal efficacy. In the optimal mixture 34 compounds were identified, which represent 98.65% of the total composition, with cinnamaldehyde (37.77%), β-caryophyllene (13.92%), methyl eugenol (12.27%) and cuminaldehyde (8.99%) being the major components. Next, we developed emulsions by combining the optimal mixture with several surfactants and determined particle size, Zeta potential, stability and bioactivity. Emulsions containing 2% and 5% Tween 20 or Tween 80 remain stable after 14 days at 54 °C. Finally, optimized emulsion retained a high acaricidal activity against larval and adult R. microplus ticks. Taken together, our findings showed the usefulness of mixture design method for the development of essential oil mixtures with potent acaricidal activity. These formulations have the potential to successfully control tick infestations.

Semisynthesis of novel N-acyl/sulfonyl derivatives of 5(3,5)-(di)halogenocytisines/cytisine and their pesticidal activities against Mythimna separata Walker, Tetranychus cinnabarinus Boisduval, and Sitobion avenae Fabricius.

To discover novel natural product-based pesticidal agents for crop protection, a series of N-acyl/sulfonyl derivatives of 5(3,5)-(di)halogenocytisines/cytisine were prepared by structural modifications of cytisine. Their pesticidal activities were evaluated against three typically crop-threatening agricultural pests, Mythimna separata Walker, Tetranychus cinnabarinus Boisduval, and Sitobion avenae Fabricius. Compound 5f exhibited the promising pesticidal activities against three tested pests. All N-phenylsulfonylcytisine derivatives showed potent acaricidal activity. Compound 5j exhibited 2.5-fold more potent acaricidal activity than cytisine, and showed good control effects. Intermediates 2, and 3/3' displayed pronounced aphicidal activity. Some interesting results of structure-activity relationships were also obtained. These results demonstrate that compounds 5f and 5j could be further modified as pesticidal agents. © 2019 Society of Chemical Industry.

Isolation and Characterization of New 16-Membered Macrolides from the aveA3 Gene Replacement Mutant Strain Streptomyces avermitilis TM24 with Acaricidal and Nematicidal Activities.

Polyketides represent an important class of biologically active and structurally diverse compounds found in nature. They are biosynthesized from acyl CoA precursors by polyketide synthases (PKSs). The use of combinatorial biosynthesis to form hybrid PKSs is considered to be an excellent approach for the development of novel polyketides. Here, 10 new 16-membered macrolide compounds were isolated from the broth of the genetically engineered strain Streptomyces avermitilis TM24, in which the PKS gene aveA3 was seamlessly replaced by the milbemycin PKS gene milA3. Their structures were elucidated on the basis of NMR and MS spectroscopic analyses. The acaricidal and nematicidal activities of them against Tetranychus cinnabarinus and Bursaphelenchus xylophilus were tested. The results indicated that compound 1 had potent acaricidal activity against adult mites with an LC50 value of 0.0022 mg L-1, while compounds 5 and 7 possessed potent nematicidal activity with LC50 values of 4.56 and 4.30 mg L-1, respectively.