Incidence and mechanisms of resistance in Bemisia tabaci with special reference to biotype Q

Transcription

1 Incidence and mechanisms of resistance in Bemisia tabaci with special reference to biotype Q R. auen, J. Benting, A. Elbert, D. Rogers, and I. Denholm* Bayer CropScience AG, Research Insecticides, Monheim, Germany *Rothamsted Research, Harpenden, UK

2 Two important biotypes of Bemisia tabaci Bemisia tabaci (sweetpotato whitefly) Q-type B-type Two important biotypes are B- and Q-types. The most dominant biotype world-wide is B, whereas Q is to a greater or lesser extent restricted to the Mediterranean basin (e.g. Almeria Spain). Esterase banding pattern to differentiate biotypes

3 Resistance monitoring in Almeria, Spain Almeria, Spain Mortality, % SUD-S ALM-2 ESP-6 ESP-98 ESP ppm Imidacloprid Thiamethoxam Acetamiprid auen et al. (22) Pest. Manag. Sci. 58

4 Spread of neonicotinoid resistance and Q-biotypes in the Mediterranean basin Bemisia tabaci

5 Biochemistry of neonicotinoid resistance Bemisia tabaci Target site insensitivity Resistance enzyme levels Esterases Glutathione S-transferases Monooxygenases Synergism Metabolism in vivo

6 Biochemistry of imidacloprid resistance in whiteflies (negative systems) Bemisia tabaci Target site insensitivity Resistance enzyme levels Esterases GST s Monooxygenases Synergism Metabolism in vivo % Total binding 1 9 Receptor binding log[imidacloprid], M SUD-S E99-2 IT-99 ESP- GER-1 USA-B ISR-2 md/min/µg protein SUD-S USA-B E99-2 IT-99 ESP- Esterases GER-1 VE-2 ISR-2 1-A 1-B fluorescence/2 min/µg protein Glutathione S-transferases SUD-S USA-B ALM-99 IT-99 ESP- GER-1 VE-2 ISR-2 Rauch & auen (23) Arch Insect Biochem Physiol. 54

7 Monooxygenases confer neonicotinoid resistance in Bemisia tabaci Bemisia tabaci ADPH+H +, 2 H 5 C 2 - H 2 H + H 3 C CH RF pmol/3min/mg protein SUD-S USA-B E99-2 IT-99 ESP- GER-1 VE-2 ISR-2 > Ethoxycoumarin--deethylase activity is a biochemical marker linked to neonicotinoid resistance in Bemisia tabaci Rauch & auen (23) Arch. Insect Biochem. Physiol. 54

8 Elevated Cyt P-45 activity confers neonicotinoid cross resistance Cl H 2 Cl S CH 3 2 Cl CH 3 CH 3 C pmol/3min/mg protein R2 =.89, LC imidacloprid, ppm 5 pmol/3min/mg protein R2 =.82, LC thiamethoxam, ppm 5 pmol/3min/mg protein R2 =.75, LC acetamiprid, ppm 5

9 Synergism + 1 ppm PB + 16 ppm IMI 1 2d Mortality, % ppm [Imi, conc.] 4ppm P Imidacloprid Imi + PB Imi + PPP Inhibitors of monooxygenases

10 nly one biochemical mechanism of resistance to neonicotinoid insecticides was found in five years of research: Microsomal monooxygenases SUD-S ESP- GER-1 I 5, nachr Cl H nm 2ml glass vials 5, dpm coated Transfer of 5 adults 24h exposure Homogenisation Centrifugation Supernatant TLC IMI Cl H H 2 23 nm Rauch & auen (23) Arch Insect Biochem Physiol. 54

11 Biochemistry of neonicotinoid resistance molecular analysis of B. tabaci P45 genes identified cyp6a14a levels linked to neonicotinoid resistance* Cyp6A 14A-Expression 12, 1, RF = 16 RF >1 8, 6, 4, RF = 4 2,, USA ISR JMB MEX2 Kreta-res Crete *Data kindly provided by Dr. Juergen Benting (Bayer CropScience, Monheim, Germany)

12 Acetamiprid-selected whiteflies are highly cross-resistant to thiamethoxam, but not vice versa! Cl Acetamiprid (ippon Soda) Me Me C Cl S Thiamethoxam * (Syngenta) 2 Me Cl S H Clothianidin * (SumiTake / Bayer AG) H Me 2

13 Insecticide cross-resistance in several strains of Bemisia tabaci Strain rigin Date Host plant Biotype CRE4-1 Crete 24 Tomato Q BR-JM3 Brazil 23 Tomato B ISR-2 Israel 22 rnamentals B MEX3-2 Mexico 23 Tomato B TUC-3 USA 23 Melon B ESP- Spain 2 Pepper Q ALM-1 Spain 1994 Tomato Q 12 (!) different whitefly insecticides (i.e. covering all relevant chemical classes commercially available) were tested in a leafdip bioassay (3-4d) against all strains,

14 Strain SUD-S (insecticide susceptible) * nymphs

15 Strain ESP- (Q-type) * nymphs

16 eonicotinoid cross-resistance in Bemisia tabaci IMI = Imidacloprid TMX = Thiamethoxam DTF = Dinotefuran IMI 3 2 ALM-1 (1994) DTF 3 DTF y = 1,4592x - 54,2 R 2 =,9289 TMX y =,472x + 23,26 R 2 =,79 IMI y =,6622x + 186,2 R 2 =,748 TMX Q-type B-type Correlated are efficacy indices for the compounds displayed. An efficacy index results from mortality figures scored at different concentrations and subsequently summarized.

17 Alignment of DFT/BP/SVP/CSM optimized geometries of neonicotinoids The alignment was done by minimization of the mutual spatial distance of three pharmacophoric points, namely (i) the positively charged C-atom connected to the - 2 and -C moiety (ii) the nitro/cyano groups themselves (iii) the nitrogens of the aromatic rings Dinotefuran

18 Pymetrozine is clearly cross- resistant to neonicotinoids in Bemisia tabaci as results from leaf-dip bioassays revealed IMI = Imidacloprid PYM = Pymetrozine 5 4 PYM y = 1,2786x - 144,3 R 2 =, IMI Correlated are efficacy indices for the compounds displayed. An efficacy index results from mortality figures scored at different concentrations and subsequently summarized.

19 Efficacy of spiromesifen and endosulfan against Bemisia tabac is not correlated w/ neonicotinoid resistance as leaf-dip bioassays revealed SPM 3 2 EDS y =,16x + 333,49 IMI IM I R 2 =,7316 Correlated are efficacy indices for the compounds displayed. An efficacy index results from mortality figures scored at different concentrations and subsequently summarized. IMI = Imidacloprid SPM = Spiromesifen EDS = Endosulfan

20 Spiromesifen* is highly active against neonicotinoid resistant whiteflies and a new chemical tool in IRM Active against whitefly nymphs (all stages) Active against adults at high concentrations Bemisia tabaci * Reduction of adult fecundity (fewer eggs) Transovarial effects on egg hatch ew IRAC MoA Group 23

21 Summary There is cross-resistance between all neonicotinoid insecticides in field-collected strains of B. tabaci, i.e. selecting with one will impact performance of all others Pymetrozine seems to be cross-resistant to neonicotinoids eonicotinoids are most likely detoxified by oxidative metabolism as elevated P45 levels, synergist studies and in vivo metabolism experiments revealed eonicotinoid resistance in B- and Q-biotypes is conferred by different cytochrome P45 s o target site insensitivity yet found Spiromesifen is a new chemical option and tool for whitefly resistance management