Toxicology of spinosad:

Transcription

1 Toxicology of spinosad: Discovery, mode of action, current uses, and detection of resistance Andy Lima, Clarke Entomologist of the Eastern Region Virginia Mosquito Control Association Hampton, VA February 6 th, 2013

2 Discovery and Description Mode of Action Chemical Classification Use in Agriculture Use in Public Health Resistance Development Resistance Management Overview

3 Discovery of a new soil-dwelling organism (1982) unknown bacterial actinomycete isolated from soil collected in Caribbean. Dr. John Mynderse Insecticidal properties detected and screened through the 1980s. (1989) merger of Eli Lilly and Dow-Elanco formed Dow Agrosciences.

4 (1990) Mertz and Yao described Saccharopolyspora spinosa Detected novel metabolites exhibiting unusual activity. Gram-positive soil-dwelling actinomycete Differentiated into substrate and aerial hyphae Spore chains with beadlike appearance Saccharopolyspora = sugar-loving many spores spinosa = spiny Refers to the spore sheath, covered in spines. Description

5 Mode of action for spinosyns Neurotoxins Spinosyns bind to nicotinic acetylcholine receptor (nachr) and GABA receptors Mimic acetylcholine acting as agonists to activate the nachr. Creates action potentials (electric signals) that convey impulses along neurons. Acts on central nervous system via neuron hyper-excitation mechanisms. Involuntary muscle contractions/convulsion Prostration with tremors paralysis Death

6 Synaptic junction in insect nervous system

7 Chemical Classification Insecticide Resistance Action Committee (IRAC), Category 5 the nicotinic acetylcholine receptor allosteric activators Spinosyns the natural and semi-natural derivatives of the fermentation of Saccharopolyspora spinosa. Spinosad Active components are spinosyns A and D Spinetoram Active components are spinosyns J and L

8 What makes spinosad special? New class of insecticide Unique mode of action No cross-resistance with other classes of insecticide Highly active on target pests, low toxicity to nontargets OMRI certification reduced risk by EPA Does not leach, bioaccumulate, volatilize or persist in the environment First new A.I. in a mosquito larvicide in more than 2 decades

9 A new active ingredient for agriculture DAS found that S. spinosa was effective against a variety of pests, including mosquitoes Pursued agricultural formulations instead of public health Hoped to create one of the world s most successful crop protection agents

10 Commercial Use (Agriculture) Spinosad was registered in 1997 under the trade name Tracer Control phytophagous crop pests OMRI certification Favorable environmental profile First pesticide classified as reduced risk by the EPA Received Presidential Green Chemistry Award in 1999

11 Widespread use in agriculture Formulations of spinosad in 73 countries, >250 crops Control of pests in the insect orders Lepidoptera, Diptera, and Thysanoptera. Also Coleoptera and Orthoptera that consume large amounts of foliage

12 The path to mosquito control (2002) Academic labs began testing serial dilutions of agricultural products against mosquitoes. Dow Agrosciences partners with Clarke Mosquito Control to develop mosquito larvicide

13 Recent studies using spinosad in field and laboratory efficacy trials Author Year Formulation (concentration) Larval mosquito species Location (habitat) Bond et al Tracer Naturalyte Insect Control (480 g AI/L) Ae. aegypti An. albimanus Cx. spp Cetin et al Conserve SC (120 g AI/L) Cx. pipiens Darriet et al Technical material of spinosad Darriet and Corbel 2006 Technical material of pyriproxyfen and spinosad Romi et al Laser (4.8% EC) Perez et al Tracer Naturalyte Insect Control (480 g AI/L) Ae. aegypti Cx. quinquefasciatus An. gambiae Ae. aegypti Ae. aegypti An. stephensi Cx. pipiens Ae. aegypti Sadanandane et al (0.5% granule, 12% SC) Cx. quinquefasciatus Mexico (lab, plastic tubs outdoors) Turkey (lab, septic tanks) (lab) (lab) (lab) Mexico (lab, black plastic containers in graveyard) India (cesspits, drains, disused wells) Thavara et al (direct application tablet, 0.5% granules) Ae. aegypti Thailand (earthen water-storage jars) Jiang and Mulla 2009 Technical material of spinosad (90.4% vs. 120 SC 11.6% AI) Anderson et al Natular XRT (6.25% spinosad) Culex spp. Cx. pipiens Cx. restuans Oc. japonicus California (lab, plastic tubs) Connecticut (catch basins)

14 A challenge for Clarke scientists (2003) Goal: create 6 OMRI-certified formulations using spinosad as A.I. (2008) Result: NATULAR Marie Saunders, chief formulation scientist

15 2004 Research and Development

16 2009 Natular on the market 5 formulations certified for use in organic operations in the U.S. 1 formulation certified for use in potable water internationally 2/6 designed for singlebrood 4/6 designed for multiple broods (30 to 180-day extended release) Production occurs in LEEDcertified facility, 100% organic

17 It ain t easy bein green Dow Agrosciences Presidential Green Chemistry Award 1999 (spinosad for agricultural use) 2008 (spinetoram for agricultural use Clarke Presidential Green Chemistry Award 2009 (spinosad for public health)

18 Reports of resistance in agricultural pests 6 species have exhibited resistance to the spinosyns in the field, most under intense selection pressure Diptera (2) House fly Lepidoptera (3) Diamondback moth Tobacco budworm Thysanoptera (1) Western flower thrip

19 Resistance in mosquitoes Su and Cheng (2012) recent AMCA publication Goal: examine resistance to spinosad in Culex quinquefasciatus in a laboraory environment. Utilized wild-caught and lab-reared mosquitoes under intense selection pressures Exposed larvae to sublethal doses of Natular G (2.5% spinosad), rearing surviving progeny Results: spinosad tolerance in F 1-9 generations, moderate resistance at F generations.

20 Mechanism of resistance to spinosyns No cross-resistance to other insecticide classes Share target sites, but mode of action is different Single recessive gene/incomplete locus? In-line with presence of a target site-based resistance mechanism. Better than metabolic pathways, the most widespread resistance mechanism Mutation in the nachr subunit gene Produces transcripts with premature stop codons Leads to insensitivity of nachr to spinosad Most recent presumed resistance mechanism

21 Insecticide Resistance Management (IRM) Decrease in susceptibility of an insect population due to a genetically controlled mechanism repeated failure of a product to achieve the expected level of control when used according to the label recommendation for that pest species Altered binding site, modified metabolism, behavioral change Multiple mechanisms may be present Spinosad's unique mode of action, lack of cross resistance, selectivity that leaves predacious insects, and moderate residual profile result in a low probability of resistance development. DAS products and Clarke products containing spinosyns as the A.I. have incorporated IRM recommendations directly on label. Extend life of Class 5 insecticides

22 What s next for the spinosyns? The first formulations utilizing spinetoram have recently become available from DAS DAS received Presidential Green Chemistry Award in 2008 for synthesis Delegate and Radiant Semi-natural derivative of S. spinosa Spinosyns J and L modified for toxicity by a chemical reaction.

23 Questions???