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PubMed2007

Resistance and cross-resistance to imidacloprid and thiamethoxam in the Colorado potato beetle Leptinotarsa decemlineata.

One of the major challenges in managing the Colorado potato beetle, Leptinotarsa decemlineata (Say) is its remarkable ability to develop resistance to virtually every insecticide that has ever been used against it. Resistance is particularly common throughout northeastern USA as far north as Maine. The first instances of resistance to imidacloprid have already been reported from several locations in New York, Delaware and southern Maine. Rotating insecticides with different modes of action may delay insecticide resistance, but successful implementation of this technique depends on a good understanding of resistance and cross-resistance patterns in populations of target pests. LC(50) values were measured for imidacloprid and thiamethoxam in Colorado potato beetle populations from a variety of locations in the USA and Canada using diet incorporation bioassays. The field performance of imidacloprid, thiamethoxam and clothianidin against imidacloprid-resistant beetles on a commercial potato farm in southern Maine was also evaluated. Correlation between LC(50) values for imidacloprid and thiamethoxam was highly significant, even when populations previously exposed to thiamethoxam were excluded from the analysis. There was no statistically detectable difference in the LC(50) values between populations exposed to both insecticides and to imidacloprid alone. Applications of neonicotinoid insecticides at planting delayed build-up of imidacloprid-resistant beetle populations on field plots by 1-2 weeks but failed to provide adequate crop protection. Consistently with bioassay results, there was also substantial cross-resistance among the three tested neonicotinoid insecticides. Results of the present study support the recommendation to avoid rotating imidacloprid with thiamethoxam as a part of a resistance management plan.

Animals↗

PubMed2001

Structure and diversity of insect nicotinic acetylcholine receptors.

The nicotinic acetylcholine receptor (nAChR) is an agonist-regulated ion-channel complex responsible for rapid neurotransmission. The vertebrate nAChR, assembled from five homologous subunits, penetrates the synaptic membrane. Different subunit combinations lead to receptor subtypes with distinctive pharmacological profiles. In comparison with mammalian nAChRs, the insect receptor is poorly understood relative to functional architecture and diversity. Several genes for Drosophila, Locusta and Myzus encoding insect nAChR subunits have been identified, although the functional assembly and presence of different subtypes of these receptors are not defined. The insect nAChR is the primary target site for the neonicotinoid insecticides, thereby providing an incentive to explore its functional architecture with neonicotinoid radioligands, photoaffinity probes and affinity chromatography matrices. This review considers the current understanding of the structure and diversity of insect nAChRs based mainly on recent studies in molecular biology and protein biochemistry.

Animals↗

PubMed2002

Desnitro-imidacloprid activates the extracellular signal-regulated kinase cascade via the nicotinic receptor and intracellular calcium mobilization in N1E-115 cells.

Imidacloprid (IMI) is the principal neonicotinoid (the only major new class of synthetic insecticides of the past three decades). The excellent safety profile of IMI is not shared with a metabolite, desnitro-IMI (DNIMI), which displays high toxicity to mammals associated with agonist action at the alpha4beta2 nicotinic acetylcholine receptor (nAChR) in brain. This study examines the hypothesis that IMI, DNIMI, and (-)-nicotine activate the extracellular signal-regulated kinase (ERK) cascade via primary interaction with the alpha4beta2 nAChR in mouse neuroblastoma N1E-115 cells. These three nicotinic agonists induce phosphorylation of ERK (p44/p42) in a concentration-dependent manner with an optimal incubation period of 30 min. DNIMI (1 microM)-induced ERK activation is blocked by nicotinic antagonist mecamylamine but not by alpha-bungarotoxin and muscarinic antagonist atropine. This activation is prevented by intracellular Ca(2+) chelator BAPTA-AM but not by removal of external Ca(2+) using EGTA and Ca(2+)-free medium. 2-Aminoethoxy-diphenylborate, a blocker for inositol 1,4,5-trisphosphate (IP(3))-mediated Ca(2+) release from intracellular stores, inhibits DNIMI-induced ERK activation but a high level of ryanodine (to block ryanodine receptor-mediated Ca(2+) release) does not. The inhibitor U-73122 for phospholipase C (to suppress IP(3) production) prevents ERK activation evoked by DNIMI. Inhibitors for protein kinase C (PKC) (GF109203X) and ERK kinase (PD98059) block this activation whereas an inhibitor (H-89) for cyclic AMP-dependent protein kinase does not. Thus, neonicotinoids activate the ERK cascade triggered by primary action at the alpha4beta2 nAChR with an involvement of intracellular Ca(2+) mobilization possibly mediated by IP(3). It is further suggested that intracellular Ca(2+) activates a sequential pathway from PKC to ERK.

Animals↗

PubMed2006

Influence of light in acute toxicity bioassays of imidacloprid and zinc pyrithione to zooplankton crustaceans.

The acute toxicity of imidacloprid, a neonicotinoid insecticide, and zinc pyrithione (Zpt), a biocide used in anti-dandruff shampoos and protective antifouling paints, to three species of ostracods and two waterfleas, including Daphnia magna, was determined and compared under light and dark conditions. Under normal laboratory conditions, UV light had no significant influence on the outcome of toxicity bioassays, although in the case of imidacloprid both EC(50) and LC(50) calculated values were twice as high under the light as in the dark. No influence of UV light was observed on bioassays conducted with Zpt, in spite of the fast aqueous photolysis exhibited by this compound. Imidacloprid 48-h LC(50) for cladocerans (65-133mg/L) were two orders of magnitude higher than for ostracods (301-715microg/L); values of EC(50) for cladocerans and ostracods were 2-6mg/L and 3-16microg/L, respectively. Toxicity of Zpt to both ostracod and cladoceran species appears to be similar, with 48-h LC(50) in the range 137-524 and 75-197microg/L for ostracods and cladocerans, respectively, and similar values for EC(50)s. The mortality endpoint (LC(50)), however, is not a reliable predictor of the effects of imidacloprid under field situations (e.g. rice paddies), because the paralysis effect induced by this insecticide takes place at much lower concentrations than those required to cause the death of the animals: regardless of the taxa, differences as large as 100- or 600-fold were observed between the EC(50) and LC(50) for the same exposures. As a consequence, immobilization tests and EC(50) values are recommended for this class of compounds, while caution should be exercised in environmental risk assessments of this and possibly other related neonicotinoid insecticides with similar activity.

Animals↗

PubMed2004

Desensitizing and non-desensitizing subtypes of alpha-bungarotoxin-sensitive nicotinic acetylcholine receptors in cockroach neurons.

Two alpha-bungarotoxin-sensitive nicotinic receptor subtypes in cockroach neurons are identified as desensitizing (nAChD), selectively inhibitable with 100 nM imidacloprid, and non-desensitizing (nAChN), selectively inhibitable with 100 pM methyllycaconitine. Although the desensitization rate of nAChD receptors is highly variable, pharmacology is largely independent of desensitization rate. Because desensitized states tightly bind agonists, nAChD receptors are potently inhibited by neonicotinoids and specifically measured in radiolabeled imidacloprid binding assays. However, they are not usually detected in binding assays with radiolabeled alpha-bungarotoxin, which has a Kd for the resting state of 21 nM, but binds poorly to desensitized states often present in binding assays. In contrast, nAChN receptors are specifically measured in binding assays with radiolabeled alpha-bungarotoxin, which binds them with a Kd of 1.3 nM. nAChN receptors are activated by neonicotinoids at micromolar concentrations, and allosterically by spinosyn A, with an EC50 of 27 nM. Spinosyn A weakly antagonizes nAChD receptors -23% at 10 microM. The roles of the two nAChR subtypes in insecticide poisoning are discussed.

Acetylcholine↗

PubMed2005

Comparison of exclusion and imidacloprid for reduction of oviposition damage to young trees by periodical cicadas (Hemiptera: Cicadidae).

Insecticides are traditionally used to control periodical cicadas (Homoptera: Cicadidae) and to reduce associated injury caused by oviposition. However, research has shown that conventional insecticides have low or variable season-long efficacy in reducing injury caused by cicadas. New systemic neonicotinoid insecticides provide excellent levels of control against a variety of sucking insects. We compared the efficacy of a neonicotinoid insecticide, imidacloprid, and a nonchemical control measure, netting, to reduce cicada injury. Netted trees sustained very little injury, whereas unprotected trees were heavily damaged. Fewer eggnests, scars, and flags were observed on trees treated with imidacloprid compared with unprotected trees; however, the hatching of cicada eggs was unaffected by imidacloprid.

Animals↗

PubMed2007

Nicotinic acetylcholine receptors: targets for commercially important insecticides.

Nicotinic acetylcholine receptors (nAChRs) are major excitatory neurotransmitter receptors in both vertebrates and invertebrates. In insects, nAChRs are the target site for several naturally occurring and synthetic compounds that exhibit potent insecticidal activity. Several compounds isolated from plants are potent agonists or antagonists of nAChRs, suggesting that these may have evolved as a defence mechanism against insects and other herbivores. Nicotine, isolated from the tobacco plant, has insecticidal activity and has been used extensively as a commercial insecticide. Spinosad, a naturally occurring mixture of two macrocyclic lactones isolated from the microorganism Saccharopolyspora spinosa, acts upon nAChRs and has been developed as a commercial insecticide. Since the early 1990s, one of the most widely used and rapidly growing classes of insecticides has been the neonicotinoids. Neonicotinoid insecticides are potent selective agonists of insect nAChRs and are used extensively in both crop protection and animal health applications. As with other classes of insecticides, there is growing evidence for the evolution of resistance to insecticides that act on nAChRs.

Animals↗

PubMed2005

Pharmacological profiles of recombinant and native insect nicotinic acetylcholine receptors.

Nicotinic acetylcholine receptors (nAChRs) are targets for insect-selective neonicotinoid insecticides exemplified by imidacloprid (IMI) and mammalian-selective nicotinoids including nicotine and epibatidine (EPI). Despite their importance, insect nAChRs are poorly understood compared with their vertebrate counterparts. This study characterizes the [(3)H]IMI, [(3)H]EPI, and [(3)H]alpha-bungarotoxin (alpha-BGT) binding sites in hybrid nAChRs consisting of Drosophila melanogaster (fruit fly) or Myzus persicae (peach-potato aphid) alpha2 coassembled with rat beta2 subunits (Dalpha2/Rbeta2 and Mpalpha2/Rbeta2) and compares them with native insect and vertebrate alpha4beta2nAChRs. [(3)H]IMI and [(3)H]EPI bind to Dalpha2/Rbeta2 and Mpalpha2/Rbeta2 hybrids but [(3)H]alpha-BGT does not. In native Drosophila receptors, [(3)H]EPI has a single high-affinity binding site that is independent from that for [(3)H]IMI and, interestingly, overlaps the [(3)H]alpha-BGT site. In the Mpalpha2/Rbeta2 hybrid, [(3)H]IMI and [(3)H]EPI bind to the same site and have similar pharmacological profiles. On considering both neonicotinoids and nicotinoids, the Dalpha2/Rbeta2 and Mpalpha2/Rbeta2 receptors display intermediate pharmacological profiles between those of native insect and vertebrate alpha4beta2 receptors, limiting the use of these hybrid receptors for predictive toxicology. These findings are consistent with the agonist binding site being located at the nAChR subunit interface and indicate that both alpha and beta subunits influence the pharmacological properties of insect nAChRs.

Animals↗

PubMed2006

Exploring the pharmacological properties of insect nicotinic acetylcholine receptors.

Insect nicotinic acetylcholine (nACh) receptors are molecular targets of insecticides such as neonicotinoids that are used to control disease-carrying insects and agricultural pests. To date, several insect nACh receptor subunits have been identified, indicating different nACh receptor subtypes and pharmacological profiles. Because of the difficulty in expressing functional insect nACh receptors in heterologous systems, new research tools are needed. Studies on insects resistant to the insecticide imidacloprid and on laboratory-generated hybrid and chimaeric nACh receptors in vitro have provided information about the molecular basis of receptor diversity, neonicotinoid resistance and selectivity. Additionally, recent results indicate that the sensitivity of insect nACh receptors to imidacloprid can be modulated by intracellular phosphorylation mechanisms, which offers a new approach to studying insect nACh receptor pharmacology.

Animals↗

PubMed2003

Microarray analysis of cytochrome P450 mediated insecticide resistance in Drosophila.

Insecticide resistance in laboratory selected Drosophila strains has been associated with upregulation of a range of different cytochrome P450s, however in recent field isolates of D. melanogaster resistance to DDT and other compounds is conferred by one P450 gene, Cyp6g1. Using microarray analysis of all Drosophila P450 genes, here we show that different P450 genes such as Cyp12d1 and Cyp6a8 can also be selected using DDT in the laboratory. We also show, however, that a homolog of Cyp6g1 is over-expressed in a field resistant strain of D. simulans. In order to determine why Cyp6g1 is so widely selected in the field we examine the pattern of cross-resistance of both resistant strains and transgenic flies over-expressing Cyp6g1 alone. We show that all three DDT selected P450s can confer resistance to the neonicotinoid imidacloprid but that Cyp6a8 confers no cross-resistance to malathion. Transgenic flies over-expressing Cyp6g1 also show cross-resistance to other neonicotinoids such as acetamiprid and nitenpyram. We suggest that the broad level of cross-resistance shown by Cyp6g1 may have facilitated its selection as a resistance gene in natural Drosophila populations.

Animals↗

PubMed2006

Establishment of baseline susceptibility data to various insecticides for Homalodisca coagulata (Homoptera: Cicadellidae) by comparative bioassay techniques.

Homalodisca coagulata Say, adults from three locations in California were subjected to insecticide bioassays to establish baseline toxicity. Initially, two bioassay techniques, petri dish and leaf dip, were compared to determine the most useful method to establish baseline susceptibility data under laboratory and greenhouse conditions. Comparative dose-response data were determined by both techniques to endosulfan, dimethoate, cyfluthrin, and acetamiprid. Toxic values were similar to some insecticides with both techniques but not for all insecticides, revealing susceptibility differences among the three populations of H. coagulata. In subsequent tests, the petri dish technique was selected to establish baseline susceptibility data to various contact insecticides. A systemic uptake bioassay was adapted to estimate dose-mortality responses to a systemic insecticide, imidacloprid. A 2-yr comparison of toxicological responses showed all three populations of H. coagulata to be highly susceptible to 10 insecticides, including chlorpyrifos, dimethoate, endosulfan, bifenthrin, cyfluthrin, esfenvalerate, fenpropathrin, acetamiprid, imidacloprid, and thiamethoxam. In general, two pyrethroids, bifenthrin and esfenvalerate, were the most toxic compounds, followed by two neonicotinoids, acetamiprid and imidacloprid. The LC50 values for all insecticides tested were lower than concentrations used as recommended field rates. Baseline data varied for the three geographically distinct H. coagulata populations with the petri dish technique. Adult H. coagulata collected from San Bernardino County were significantly more susceptible to select pyrethroids compared with adults from Riverside or Kern counties. Adults from San Bernardino County also were more sensitive to two neonicotinoids, acetamiprid and imidacloprid. The highest LC50 values were to endosulfan, which nonetheless proved highly toxic to H. coagulata from all three regions. In the majority of the tests, mortality increased over time resulting in increased susceptibility at 48 h compared with 24 h. These results indicate a wide selection of highly effective insecticides that could aid in managing H. coagulata populations in California.

Animals↗

PubMed2006

Use of residue profile analysis to identify modes of insecticide activity contributing to control of plum curculio in apples.

Residue profile analysis techniques were developed, along with laboratory and field-based bioassays to describe the modes of insecticidal activity responsible for the control of the plum curculio, Conotrachelus nenuphar (Herbst), in apples (Malus spp.). Adult plum curculios were treated in laboratory topical bioassays to determine acute contact activity and lethal time for five insecticides. Azinphosmethyl had the highest levels of toxicity and shortest lethal time values, followed by the neonicotinoids thiacloprid, thiamethoxam, and imidacloprid, whereas indoxacarb had the highest LD50 and LT50 values for topical exposure. Field-based residual activity bioassays assessed adult mortality, and fruit and leaf injury from plum curculio exposed to 4 h, 7 d, and 14 d field-aged residues. All compounds caused significant levels of mortality to plum curculio when adults were exposed to fruit clusters 4 h post-application. Thiacloprid, thiamethoxam, and imidacloprid showed oviposition deterrence, antifeedant, and repellency effects in the 7- and/or 14 d residual bioassays and protected fruit in the absence of significant lethal activity. Indoxacarb maintained lethal activity throughout the study intervals, with the incidence of plum curculio feeding, suggesting that ingestion is an important mode of entry. For the neonicotinoids thiacloprid, thiamethoxam and imidacloprid plum curculio mortality was highly correlated with fruit and leaf surface residues. As surface residues declined, sublethal effects such as oviposition deterrence and antifeedant effect remained. The value of the plant-insect-chemistry triad model for describing the temporal dimensions of insecticidal modes of activity and understanding a compound's critical performance characteristics is discussed.

Animals↗

PubMed2003

Biological and chemical control of the Asiatic garden beetle, Maladera castanea (Coleoptera: Scarabaeidae).

The efficacy of chemical and biological control agents against larvae of the Asiatic garden beetle, Maladera castanea (Arrow), in turfgrass under laboratory, greenhouse, and field conditions were determined. In field trials where insecticides were applied preventively against eggs and young larvae, the molt-accelerating compound halofenozide and the neonicotinoids imidacloprid and thiamethoxam were ineffective, whereas another neonicotinoid, clothianidin, provided 62-93% control. In greenhouse experiments against third instars in pots, the carbamate insecticide carbaryl was ineffective, whereas the organophosphate trichlorfon provided 71-83% control. In laboratory, greenhouse, and field experiments, the entomopathogenic nematode Heterorhabditis bacteriophora Poinar and Steinernema glaseri Steiner (not tested in the field) were ineffective against third instars, whereas S. scarabaei Stock & Koppenhöfer provided excellent control. In microplot field experiments at a rate of 2.5 x 10(9) infective juveniles per ha, H. bacteriophora provided 12-33% control and S. scarabaei 71-86% control. Combinations of S. scarabaei and imidacloprid did not provide more control of third instars compared with S. scarabaei alone.

Animals↗

PubMed2001

Imidacloprid-induced facilitation of the proboscis extension reflex habituation in the honeybee.

Imidacloprid is a new insecticide from the family of the neonicotinoids, which interact with the insect nicotinic acetylcholine receptor. The effects of imidacloprid at a dose that does not affect sensory or motor functions are studied on non-associative learning abilities in the honeybee. The behavioral procedure is the habituation of the proboscis extension reflex (PER). Imidacloprid topically applied on the thorax (1 microl) at the doses of 5, 10, and 20 ng/bee induces an increase of the gustatory threshold defined as the lowest concentration of a sucrose solution applied to the antennae able to elicit the PER. The ability of the honeybee to move in an open-field-like apparatus is impaired at the doses of 2.5, 5, 10, and 20 ng/bee. These effects are amplified with time and reach a maximum 60 min after application. The lowest dose of 1.25 ng/bee has no effect on the gustatory function but increases the motor activity and facilitates the PER habituation independently of time. This result fits our hypothesis that a slight activation of the cholinergic system with a low dose of imidacloprid can facilitate a simple form of learning in the honeybee.

Animals↗

PubMed2005

Synergism and stability of acetamiprid resistance in a laboratory colony of Plutella xylostella.

The involvement of metabolic enzymes in the resistance of a laboratory colony of diamondback moth, Plutella xylostella (L), to the neonicotinoid insecticide acetamiprid was determined with the synergists piperonyl butoxide (PBO), which suppresses the activity of cytochrome P-450 monooxygenases, and S,S,S-tributyl phosphorotrithioate (DEF), an inhibitor of esterases, using the leaf-dipping method. Both PBO and DEF enhanced the insecticidal activity of acetamiprid significantly in the resistant P. xylostella strain but not in a reference strain, suggesting that cytochrome P-450 monooxygenases and esterases play an important role in the resistance of P. xylostella to acetamiprid. The resistant P. xylostella strain was also reared without further exposure to acetamiprid to determine the stability of resistance. Maintaining the resistant strain for seven generations in the absence of selection pressure resulted in a drop in resistance ratio from 110 to 2.42, indicating that acetamiprid resistance in P. xylostella is not stable.

Animals↗

PubMed2006

Identification of a high-affinity binding site for dinotefuran in the nerve cord of the American cockroach.

The binding of the neonicotinoid insecticide dinotefuran to insect nicotinic acetylcholine receptors (nAChRs) was examined by a centrifugation method using the nerve cord membranes of American cockroaches and [3H]dinotefuran (78 Ci mmol-1). The Kd and Bmax values of [3H]dinotefuran binding were estimated to be 13.7 nM and 14.8 fmol 40 microg-1 protein respectively by Scatchard analysis. Epibatidine, an nAChR agonist, showed a rather lower affinity to the dinotefuran binding site (IC50=991 nM) than dinotefuran (IC50=5.02 nM). Imidacloprid and nereistoxin displayed lower potencies than dinotefuran but higher potencies than epibatidine. The potencies of five dinotefuran analogues in inhibiting the specific binding of [3H]dinotefuran to nerve cord membranes were determined. A good correlation (r2=0.970) was observed between the -log IC50 values of the tested compounds and their piperonyl butoxide-synergised insecticidal activities (-log LD50 values) against German cockroaches. The results indicate that a high-affinity binding site for dinotefuran is present in the nerve cord of the American cockroach and that the binding of ligands to the site leads to the manifestation of insecticidal activity.

Animals↗

PubMed2006

Potential of imidacloprid to control four species of psocids (Psocoptera: Liposcelididae) infesting stored grain.

The effectiveness of the neonicotinoid insecticide imidacloprid was evaluated against four psocid pests of stored grain. This research was undertaken because of the growing importance of psocids in stored grain and the need to identify methods for their control. The mortality and reproduction of adults of Liposcelis bostrychophila Badonnel, L. entomophila (Enderlein), L. decolor (Pearman) and L. paeta Pearman in wheat treated with imidacloprid were determined. There were five application rates (0.5, 1, 2, 5 and 10 mg AI kg(-1) grain) and an untreated control. There were significant effects of application rate on both adult mortality and reproduction for all four species, but the effect of imidacloprid was sometimes more pronounced on reproduction. Imidacloprid was most effective against L. bostrychophila, with 100% adult mortality after 7 d at 5 mg AI kg(-1), 14 d at 2 mg AI kg(-1) and 28 d at 0.5 and 1 mg AI kg(-1). No live progeny were produced at 2 mg AI kg(-1). For L. decolor, there was 100% adult mortality after 28 d at 10 mg AI kg(-1) and no live progeny were produced at 2 mg AI kg(-1). For L. entomophila, there was 100% adult mortality after 14 d at 10 mg AI kg(-1) and 28 d at 2 and 5 mg AI kg(-1). No live progeny were produced at 10 mg AI kg(-1). At 10 mg AI kg(-1) there was 100% mortality of L. paeta adults after 28 d exposure and no live progeny developed. Because reproduction at some application rates occurred only in the first 14 d of exposure, it is concluded that the application rate leading to population extinction was 1 mg AI kg(-1) for L. bostrychophila, 2 mg AI kg(-1) for L. decolor and L. entomophila and 5 mg AI kg(-1) for L. paeta. This study shows that imidacloprid has potential as a grain protectant to control all four Liposcelis species in stored grain.

Animals↗

PubMed2002

Interaction of dinotefuran and its analogues with nicotinic acetylcholine receptors of cockroach nerve cords.

To investigate the action of dinotefuran (MTI-446, 1-methyl-2-nitro-3-(tetrahydro-3-furylmethyl)guanidine), a recently developed insecticide, on insect nicotinic acetylcholine receptors (nAChRs), we determined the potencies of the compound and 15 analogues in inhibiting the specific binding of [3H]epibatidine (EPI), a nAChR agonist, and [3H]alpha-bungarotoxin (alpha-BGT), a competitive nAChR antagonist, to the nerve cord membranes of American cockroaches (Periplaneta americana). Racemic dinotefuran inhibited [3H]EPI binding with an IC50 of 890 nM and [3H]alpha-BGT binding with an IC50 of 36.1 microM. Scatchard analysis indicated that the dinotefuran inhibition of [3H]EPI binding was a competitive one. Slight structural modification caused a drastic reduction in potency; only four analogues were found to be equipotent to or more potent than dinotefuran. Chloropyridinyl and chlorothiazolyl neonicotinoid insecticides displayed two or three orders of magnitude higher potency than dinotefuran. There was a good correlation between the IC50 values of tested compounds obtained with [3H]EPI and those obtained with [3H]alpha-BGT. A better correlation was observed between 3-h knockdown activities (KD50) against German cockroaches (Blattella germanica) and IC50 values obtained from [3H]EPI assays than between 24-h lethal activities (LD50) and IC50 values. While the results indicate that dinotefuran and its analogues interact with the ACh-binding site in cockroach nAChRs, it remains to be elucidated why they displayed lower potencies than those expected based on their insecticidal activities.

Animals↗