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Diamondback Moth in North America A

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Diamondback Moth in North America A 50 Insecticide Resistance of Diamondback Moth in North America A. M. Shelton and J. A. Wyman¹ New York State Agricultural Experiment Station. Geneva. New York 14456. USA 'University of Wisconsin,. Madison, Wisconsin, 53706, USA Abstract The extent and geographic distribution of resistance to methomyl, permethrin and methamidophos in 44 populations of diamondback moth, Plutella xylostella (L.) from 19 states within the U.S., Mexico, Canada and Belize was determined in 1988. Widespread resistance to all three insecticides was confirmed. Resistance was generally highest in populations originating from southern states but scattered populations with high levels of resistance were also detected in northern states. In most instances where resistance was detected to one insecticide, there was also resistance to the other two. Highest levels of resistance were detected for methomyl. During 1989, diamondback moth was imported into New York on southern cabbage transplants (seedlings). During June, when most transplants arrived in New York, DBM infestations were as high as 12.8 insects per 100 transplants on an individual shipment. Compared to a standard susceptible field population, the diamondback moth which were collected from transplants had moderate to high (> 100-fold in one case) levels of resistance to permethrin and methomyl. In 1990, eleven diamondback moth populations were surveyed for susceptibility to two commercial formulations of Bacillus thuringiensis. High levels of resistance (in some cases > 200-fold) were found in populations which originated from Florida. Introduction The diamondback moth (DBM) Plutella xylostella (L.) (Lepidoptera:Yponomeutidae)is a key pest of cruciferous crops throughout the world. In tropical and subtropical areas, crucifer production has been seriously affected in recent years by DBM which has developed resistance to a wide range of insecticides (Sun et al. 1986). Georghiou (1981) has reported DBM resistance to 36 insecticides in 14 countries. In North America DBM has normally been considered a minor pest in the lepidopteran complex, but in the last 5 years entomologists in several states (including Florida, Georgia, North Carolina, Texas, Wisconsin and New York) have reported economic damage in crucifers as a result of their inability to control DBM. Such control failures may have been influenced by environmental factors (Harcourt 1986; Sastrodihardjo 1986), but when examined on a regional basis, insecticide resistance is the most tractable cause. Our studies on the extent and development of insecticide resistance in DBM within North America occurred in three phases. In 1988 we surveyed the level of susceptibility of DBM to three commonly used synthetic insecticides (methomyl, permethrin and methamidophos) representing the three major classes of insecticides (pyrethroids, carbamates and organophosphates) used within North America. As a result of information gathered in 1988 which indicated high levels of resistance in New York, we initiated a study in 1989 to determine if resistant DBM populations in New York were the result of importing DBM on plants grown in southern states. The third phase of this study surveyed the level of susceptibility of 11 DBM populations to two commercial formulations of Bacillus thuringiensis Berliner. 447 448 Shelton and Wyman Insecticide Resistance to Methomyl, Permethrin and Methamidophos In 1988, cooperators were asked to collect 50-150 DBM larvae and pupae from commercial or research cabbage fields in their respective areas. Collections were made in each area during the peak of DBM activity. Forty-four populations from 19 states within the U.S., Mexico, Canada and Belize (Tables 1-3) were evaluated using a leaf dip bioassay similar to Tabashnik et al. (1987) for susceptibility to permethrin (Ambush 2E), methomyl (Lannate 1.8L), and methamidophos (Monitor 4E). We attempted to test all field-collected populations in the first five generations; populations from Geneva, New York, Pulehu, Hawaii, and College Station, Texas, were laboratory colonies and were tested in later generations. Data were analyzed using the POLO procedure (Russell et al. 1977) to obtain LC values. Resistance ratios (RR), the ratio of the LC50 of a given population to that of the standard population, were calculated. The standard population originated from Geneva, New York, in 1988 and was laboratory-reared for 23 generations. DBM populations exhibited extreme variation in susceptibility to methomyl (Table 1). A colony from Greenville, North Carolina had the highest RR of 780, followed by RRs of 362 Table I. Susceptibility to methomyl of DBM larval populations. LC50-48h (95% CL) Region Population N Slope ±SE RRª me AI/ml East Lochwood. CT F4 238 0.960 (0.689-1.333) 2.32±0.28 9.06 Derry. NH F3 202 3.430 (2.284-5.072) 1.5 I 20.19 32.4 Litchfield. NH F2 220 3.805 (I.798-6.706) 1.21 20.21 35.9 Fairton. NJ F4 243 4.042 (2.424-5.699) I .87 + 0.34 38. I Albion, NY F5 24 2 36.28 (I5.61-195.4) 0.77±0. 15 342 Davie. NY F1 24 I 0.926 (0.529-1.394) 3.09 ± 0.57 8.74 Geneva, NY F23 242 0.106 (0.084-0.129) 3. 12±0.68 I .00 Long Island, NY F4 25 I 9.419 (7.104-12.51) 2.14±0.33 88.9 Ransomville. NY F3 24 3 9.299 (6.226-14.62) 1.30±0.19 87.7 Dover, DE F8 246 0.883 (0.430-1.722) I .84 ±0. I9 8.33 Midwest Celeryville, OH F3 219 1.176 (0.782-1.742) I .46 ± 0. I6 11.1 Fremont. OH F2 24 I 0.428 (0.144-0.964) 1. 19±0. 15 4.04 Simcoe. ONT F2 237 4.500 (3.152-6.150) 1 .82±0.25 42.4 Lake Co.. IN F2 214 3. I 19 (I.386-6.780) 1.28±0.15 29.4 Purdue, IN F2 240 0.389 (0.268-0.563) 1.90± 0.26 3.67 Holtz. MI F4 235 1.580 (0.841-2.567) 1.90±0.25 14.9 Stolz, MI F4 200 2.905 (I.741-4.507) 1.74±0.22 27.4 Arlington, WI F3 24 I 0.5 10 (0.33 1-0.755) 2.48±0.45 4.81 Funks E. S., WI F3 233 0.287 0.94±0.44 2.71 Funks M. S., WI F3 23 5 0.2 I7 (0.167-0.276) 3.78 ± 0.80 2.05 Heldings, WI F2 237 0.293 (0.I3 1-0.603) 1.84±0.27 2.76 Poynette, WI F2 24 3 3.995 (2.778-5.587) I .68 ± 0.2 I 37.7 Pacific Nakatani, HI F2 239 3.462 (I.925-5.739) 1.55±0.19 32.7 Pulehu, HI F86 206 0.563 (0.383-1.055) 3.07 ± 0.56 5.3 I Mt. Vernon, WA F2 213 0.284 (0.22 1-0.408) 3.25 20.72 2.68 Yakima. WA F4 208 0.424 (0.308-0.637) 2.49±0.4 I 4.00 b Southwest Belize, C.A. F1 239 38.39 7.65 ± 85. I 362 Bixby. OK F2 193 0.358 (0.250-0.545) 2.05 20.33 3.38 South Donna, TX F2 235 5.126 (4.098-6.309) 3.49±0.60 48.4 Tamu. TX F9 24 1 0.544 (0.369-0.908) 2.582 0.36 5.13 Weslaco, TX F1 232 2.500 (1.417-4.1 11) 1.87±0.23 23.6 South Zellwood, FL F1 248 4.039 (2.379-5.783) 2. I3± 0.36 38. I Tifton, GA F1 235 17.96 (12.15-31.37) I.44 ± 0.26 I69 Greenville, NC F1 240 82.73 (27.2-15680) 1.06±0.26 780 Painter, VA F5 235 0.507 (0.333-0.751) 1.43±0. 17 4.78 RR is the resistance ratio determined by dividing the LC50 for a population by the LC50 for the Geneva population. Neither the 95 nor 90% CL could be estimated because g > 0.5. Insecticide Resistance in North America 449 from Belize, and 342 from Albion, New York. When classified by levels of RR, 11% of the populations had an RR > 100, 6% from 50-99, 29% from 25 to 49, 8% from 10 to 24 and 46% < 10. Resistance ratios for permethrin were lower than for methomyl (Table 2). Resistance ratios for permethrin were highest in a population collected from Albion (80.8), followed by Belize, (78.4) and Tifton, Georgia (75.9). When classified by levels of RR, 17% of the populations had RRs > 50, 8% from 25 to 49, 19% from 10 to 24 and 56% < 10. The highest RR for methamidophos was 42.3 for the population collected from Belize (Table 3). When classified by levels of RR, none of the populations had an RR > 50, 3 % from 25 to 49, 13% from 10 to 24 and 83% < 10. Table 2. Susceptibility to permethrin of DBM larval populations. LC50-48h (95% CL) Region Population N Slope ± SE RRª mg AI/ml East Lochwood, CT F2 248 0.0 I9 (0.0 10-0.030) 1.24±0.20 0.58 Dover, DE F7 I98 0.541 (0.33 1-0.830) 1.66±0.24 16.4 Derry, NH F7 243 0.709 (0.44 I-1 ,003) 1.73±0.33 21.5 Litchfield. NH F2 238 0.452 (0.289-0.699) 1.2920.15 13.7 Fairton. NJ F3 24 3 0.26 1 (0.126-0.470) 2.02±0.24 7.91 Albion, NY F4 248 2.669 (1.949-3.810) 2.41 ±0.59 80.8 Davie.
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