New Insecticide Modes of Action: Whence Selectivity?

Size: px

Start display at page:

Download "New Insecticide Modes of Action: Whence Selectivity?"

Jemimah Ramsey
6 years ago
Views:

1 New Insecticide Modes of Action: Whence Selectivity? Joel Coats Professor of Entomology and Toxicology Iowa State University Ames, Iowa utline Selectivity New Insecticide asses Neonictinoids Fipronil Chlorphenapyr Sulfluramid Spinosads Buprofezin Diafenthiauron Indoxacarb Metaflumazone Pymetrozine 1

2 Where have we been? C 3 CH DDT 2

3 dieldrin lindane 3

4 Where are we now, and where are we headed? Neonicotinoids 4

5 N NH N No 2 N Imidacloprid Imidacloprid Mode of Action Binds irreversibly to postsynaptic nicotinic acetlycholine receptors. 5

6 Neonicotinoid: : Acetylcholine Agonist nerve axon Neo ACH Neo ACH NERVE SYNAPSE Neonicotinoids Thiamethoxam Control wide range of sucking / chewing pests like aphids, thrips, termites, weevils, beetles, wireworms, fire ants 6

7 Neonicotinoids-- --Thiamethoxam Toxicity to non-targets Rat oral LD 50 a.i. = 1,563 mg/kg Rat dermal LD 50 a.i. >2,000 mg/kg Water solubility = 4,100 mg/l Fipronil 7

8 fipronil - Regent Phenyl-pyrazole family fipronil - primary family member in production F 3 C N N H 2 N S F 3 C CN Fipronil Fipronil Mode of Action Acts as an inhibitor at the γ- aminobutyric acid (GABA) receptor as a noncompetitive blocker of the GABA- gated chloride channel (similar to lindane and cyclodienes) Chemical and biological activation producing equally toxic and sometime more persistent metabolites with same mode of action 8

9 Nerve Axon - - Na+ - K + - GABA-gated Chloride Channel Fipronil Mode of Action - - Fipr - Na+ - K + - Antagonist at GABA-gated Chloride Channel 9

10 Selective Toxicity of Fipronil Vertebrate Acute Mouse ral LD 50 = 41 mg/kg Insect Acute Housefly Contact LD 50 = 0.13 mg/kg Chlorfenapyr 10

11 Chlorfenapyr Br F 3 C N CH 2 C 2 H 5 CH 3 American Cyanamid product, now BASF Registered outside U.S. for cotton Broad-spectrum insecticidal action Chlorfenapyr, AC-303,630 Chlorfenapyr xidative Phosphorylation Chemiosmotic theory Electron flow through the electron transport chain is accompanied by a transfer of protons ATP synthesis driven by proton-motive force Electron transport train uses 2 as final electron receptor 11

12 Sulfluramid H F F F F F F F CH 3 CH 2 N S C C C C C C C F F F F F F F CF 3 sulfluramid 12

13 Spinosads New class of potent natural insecticides R R 1 N H R 7 H H H H H R 2 R 4 R 5 R 6 SPINSADS R 3 13

14 Spinosads Mode of action acts on the acetylcholine receptor to make it more excitable verstimulation of the nerve results. Hypothesis currently considered most plausible, although not really accepted as the last word Acetylcholine Receptor - Spinosads nerve axon ACH ACH ACH Spyn ACH NERVE SYNAPSE 14

15 Buprofezin S N NC(CH 3 ) 3 N CH(CH 3 ) 2 buprofezin Buprofezin Mode of Action Inhibits chitin synthesis/deposition Effect similar to benzoyl phenylureas Insects die when newly molted IGR 15

16 Diafenthiuron CH(CH 3 ) 2 H N C NHC(CH 3 ) 3 S CH(CH 3 ) 2 diafenthiuron Diafenthiuron- Mode of Action Inhibits ATPase in mitochondria Blocks utilization of energy (ATP) Thiourea compound 16

17 Indoxacarb N N N CH 3 C CH 3 indoxacarb CF 3 Indoxacarb Mode of Action Blocks sodium channel in nerve axon Inhibits propagation of nerve potential xadiazine compound 17

18 Indoxacarb effect on nerve axon Na + - Indox - K + - Nerve Potential Propagation Metaflumizone 18

19 Metaflumizone Putative mode of action blocks sodium channel in nerves Log P Pymetrozine HN N N N N pymetrozine 19

20 Pymetrozine Mode of Action Inhibits feeding of sucking insects Especially active on aphids Pyridine azomethine compound Conclusions A number of very new classes of insecticides have been developed, with new modes of action. Availability of products is changing, toward newer classes of insecticides. Selectivity is ever more important: to applicators, to livestock, pets, wildlife, environment, residues in food. 20

21 Conclusions Some of the new chemistry perpetuates non-selective insecticide toxicity. Some of it allows opportunities for safer, more selective insecticides. Questions How many and which modes of action should be screened for in non-target bioassays? High throughput assays? Can we predict which species will be most vulnerable and under what exposure (conc., timing)? 21

22 The First McKim Conference: Some Important Questions Best bioassays? Specificity and selectivity? Extrapolation? Metabolic detoxification or activation? If you re not part of the solution you re part of the precipitate. - Anon (C&EN) 22

23 Getting answers depends on the quality of the hired help. Steve Bradbury, circa

24 Part of Jim McKim s rich legacy 24

Insect Control Update for 2012:

Insect Control Update for 2012: an ever changing effort! David J. Shetlar, Ph.D. The BugDoc The Ohio State University, OARDC & OSU Extension Columbus, OH January 2012, D.J. Shetlar, all rights reserved