TOXICITY OF ABAMECTIN AND HYDRAMETHYLNON TO INSECTICIDE-SUSCEPTIBLE AND RESISTANT

STRAINS OF GERMAN COCKROACH (DICTYOPTERA: BLATTELLIDAE),

J. G. Scott Department of Entomology

Comstock Hall Cornell University

Ithaca, New York 14853-0999 USA

ABSTRACT

The toxicities of two new insecticides, hydramet.hylnon and abamectin, were evaluated against one susceptible and seven insecticide-resistant strains of 81attella gennanica. (L.) Both materials proved to be potent insecticides against the susceptible strain. There was no difference in toxicity, based on LTfoO values, of hydramethylnon between resistant and susceptible strains in a feeding bioassay. Likewise. there was no significant cross-resistance to abamectin (based on LOw values) detected in seven resistant strains by topical application. However, two strains did show significant cross-resistance to ablllnectin based on LD9!. values. These results suggest that in German cockroaches cross-resistance to hydramethylnon may be rare and cross-resistance to abamectin may be limited.

Key Words: Insecta, resistance, abamectin, hydramethylnon, German cockroach, Blattella gemwnica, Dictyoptera, Blattellidac.

J. Agric. EntomoL 8(2): 77-82 (April 1991)

Insecticide resistance is a severe problem that limits our ability to control cockroaches. The Cerman cockroach, Bia/lella germanica (L.) is the most important cockroach pest in the United States, and resistance has developed to many of the insecticides used to control it (Rust and Reierson 1978, Cochran 1982, 1989). One way to maintain control of German cockroaches is through lhe judicious use of new insecticides. Although cockroaches may eventually develop resistance to these new compounds, resistance could evolve more rapidly if cross-resistance to the new insecticides is present due to previous insecticide usc.

Two new insecticides, abamectin and hydramethylnon, hold promise for the control of German cochoaches. These insecticides have a mechanism of action that is dissimilar to currently used compounds (Olsen and Snowman 1985, Hollings­haus 1987) and, therefore, may he of value for use in insecticide resistance management schemes (Georghiou 1983). Abamectin and hydrnmethylnon are toxic to German cockroaches both by topical application and by ingestion (Hollingshaus and Little ]984, Cochran 1990). Hydramethylnon is commercially available as bait (Amdro). In order to evaluate the potential for resistance to evolve to these new insecticides (via cross·resistance), their toxicities to one susceptible and seven resistant strains of German cockroach that are variously resistant to organophosphate (OP), carbamate, chlorinated hydrocarbon, and pyrethroid insecticides, were evaluated.

, Received for publicotion 3 May 1990: nccepted 7 September 1990.

77

78 J. Agric. Entomol. Vol. 8, No.2 (1991)

MATERIALS AND METHODS

Insects. Eight strains of German cockroach were used: 1) CSMA, an insecticide­susceptible strain; 2) Ectiban-R, a pyrethroid-resistant strain possessing a kdr-type resistance mechanism (Scott and Matsumura 1981, (983); 3) Kenly, a multiresistant strain having piperooyl butoxide (PBO) and S,S,S,·tributylphosphorotrithioate (DEF) suppressible resistance to propoxur and bendioc81'b (Scott et a1. 1990); 4) Rutgers, a multiresistant strain having PHO suppressible bendiocarb and malathion resistance (Scott et al. 1990; 5) Dursban-R, a multiresistant strain having mono­oxygenase and hydrolase-mediated chlorpyrifos resistance (Siegfried et aI. 1990); 6) PYR, selected from the Kenly strain using pyrcthrins; 7) CHL, a chlorpyrifos. resistant strain supplied by B. Zeichner in 1989; and 8) Navy, a pyrethroid-resistant strain supplied by D. Cochran in 1989. Cockroaches were reared as described previously (Scott et a1. 1990), and provided with dog food and water ad libitum

Bioassay. Formulated hydramethylnon (Amdro~, 1.56% AI in bait formulation, American Cyanamid, Princeton, New Jersey) t.oxicity was evaluated (as LT50'S) with 10 male cockroaches in 470-ml mason jars. After starving t.he cockroaches for 48 h, a 3.6-cm wet dental wick and 0.2-0.5 g of Amdro were placed in each jar. Dog food was used in place of Amdro for the controls. Jars were held at 25°C and water was added daily. Mortality was assessed twice daily until all the Amdro-fed cockroaches were dead. Each test was replicated 4-15 times. Abamectin toxicity was evaluated (as LD50'S) against adult males by topical application in 0.5 ~I acetone as described by Scott et al. (1990). Abamectin toxicity by feeding to susceptible and resistant cockroaches has recently been reported (Cochran 1990). Bioassay data were analyzed by standard probit analysis (Finney 1971) as adapted for personal computer use by Raymond (1985).

RESULTS AND DISCUSSION

The toxicity of hydramethylnon to susceptible and resistant cockroach strains is shown in Table 1. None of the resistant strains displayed significantly different LTfiO values (or LT95 values) (data not shown) compared with the susceptible (CSMA) strain. This suggests that the previous selection of these different resistant strains, by several insecticides, has not conferred cross·resistance to hydramethylnon.

Although hydramethylnon resistance may develop if this compound becomes widely used, it appears that the evolution of resistance would not be commonly accelerated by existing cl'oss-resist.ance in the German cockroach, and that pre­existing physiological resistance mechanisms present in these strains do not affect hydramethylnon toxicity. \Vhile any survey of cross-resistance to new compounds could overlook an important mechanism, the major mechanisms of resistance in German cockroach are likely represented in this study. Mechanisms represented by these strains include: hdr-type pyrethroid and DDT resistance, monooxygenase­mediated chlorpyrifos resistance, hydrolysis-mediated chlol'pyrifos resistance, PBO suppressible malatllion resistance, as well as PBG and DEF suppressible resistance to bendiocarb and propoxur. Altered acetylcholinesterase did not appeal' to be a mechanism of resistance t.o organophosphate 01" carbamate insecticides in any of these strains (Siegfried and Scott 1990). Additionally, three othel' resistant strains were tested in which the mechanisms have not been studied.

SCO'l'T: New Insecticides for Resistant Cockroaches 79

Table I. Toxicity of hydramethylnon by feeding to eight strains of Gelman cochoach.

Strain n Slope (± SEl LT",' (95% CIl RRt CSMA 150 11 (1.4) 76 (74 - 79)

Ectiban-R 150 9.9 (0.6) 79 (77 - 83) 1.0

Kenly GO 13 (1.2) i2 (70 -75) 0_9

Rutgers GO II (1.0) 73 (70 - 76) 1.0

PYR GO 11 (1.0) 72 (69 - 74) 0.9

~a\'y GO 11 (1.0) 73 (70 -76) 1.0

CHL GO 12 (1.1) 71 (72 - 77) 0.9

Dursban·R 40 10 (1.1) 74 (71 - 78) 1.0

• EX(lressed as houl'!O t LTMl of resisulIlt slruin/L;I'.}O of Sllscel'lible lCSMA) sLrnin.

Toxicity of abameclin to the susceptible and seven insecticide-resistant strains is listed in Table 2. Abamcctin was highly toxic to the susceptible strain, being more toxic than eight of nine insecticides previously tested (Scott et al. 1990). None of the insecticidc-resistant strains showed LDf>O values that differcd significantly (based on nonoverlap of confidence intervals) from the susceptible strain when the different body size of each strain was taken into account (Table 2). These results are in agreement with those of Cochran (1990). who found no cross-resistance to abumectin in German cockroaches when it was incorporated into food. However, LDD5 values were signiJicantly greater (based on nonoverlap of confidence intervals) in the closely related Kenly and PYR strains compared with the susceptible strain. Therefore, it appears likely that the Kenly and PYR strains are unusually hetero­geneous in their response to abameetin and that these strains are cross-resistant t.o abamectin. The Kenly (and PYR) strains are multiresistant (Scott et al. 1990, Cochran 1989) and, therefore, it is difficult to determine the insecticide that selected for cross-resistance to abamectin. The only strains for which we have a reasonably complete spectrum of resistance are Kenly, Rutgers, and Dursban-R. Based on this very limited comparison, the only unusual feature of the Kenly strain is its higher level of resistance to propoxur compared with Rutgers or Dursban-R (Cochran 1989, Scott et at 1990, Siegried et at in 1990)_ Whether or not propoxur was the insecticide that selected for the cross-resistance to abamectin will require further study.

A recent report has demonstrated abamectin cross-resistance in permethlin­selected house flies (Scott 1989). Based on the partial synergism of the cross­resistance with piperonyJ butoxide, the genetic location of the cross-resistance factors (autosomes 2 and 3) and a pre\'ious report that found no abamectin cross­resistance in hdr-resistant house nies (Roush and Wright 1986), it was concluded that. the mechanisms responsible for abamectin cross-resistance were most likely decreased cuticular penetration and increased oxidative detoxication. The results of my current study suggest that pyrethroid induced cross-resistance to abamectin is probably rare in German cockroaches.

00 0

Table 2. Toxicity of abamectin by topical application to eight strains of German cockroach.

mg Body Weight Strain n Slnpe (± SE) LD",t (95% CL) RRt LTh,t (95% CLI RR§ (X ± SE)

CSMA 170 2.3 (0.3) 0.56 (0.40 - 0.74) 2.9 ( 1.8 ­ 5.9) 44.6 ± 0.8

Ectiban· R

Kenly

180

150

2.2 (0.:1)

1.2 (0.2)

0.89 (0.72 - 1.12)

1.18 (0.72 - 2.00)

1.6

2.1

3.5

:10

( 2.5­

(10

6.4)

290 )

1.2

10 • 46.6 ± 0.8

49.9 ± 0.9

~ ,.. ~ ,.

Rutgers

PYR Navy

170

120

120

2.4 (0.4)

1.2 (0.4)

2.0 (0.3)

0.39 (0.28 - 0.51)

1.29 (0.46 - 2.22)

0.91 (0.58 - 1.27)

0.7

2.3

1.6

1.8

30

9.3

( 1.2­ 3.6)

(II - 1200 )

( 5.3­ 28 )

0.6

10 • 3.2

56.6 ± l.:J

49.8 ± 1.0

5:1.6 ± l.:J

e

'" ~ 3 ~

Dursban-R 150 2.4 (0.5) 0.33 (0.27 - 0.58) 0.6 1.4 ( 0.9­ 3.8) 0.5 49.2 ± l.l ~ CHL 120 1.6 (0.4) 0.51 (0.28 - 0.77) 0.9 6.0 ( 2.8­ 41 ) 2.1 53.1 ± 1.0 SX'

t IJI>( insecticide per g body weigh!. Z 9

:j: LD~ rt'sistant strain/LD~o suscept.ible (CSMA) strain. ~

§ LD",·, resistant straill/LD~:. !'usceptible strain. • Significantly different from CSMA (p < 0.05) based on nonoverlap of confidence intervals. <0

~

81 SCOTT: New Insecticides for Resistant Cockroaches

In summary, no cross-resistance was detected to hydramethylnon in seven insecticide-resistant strains of German cockroach, while cross-resistance to abamectin was found in two (closely related) of the seven strains. This suggests that these insecticides (especially hydramethylnon) will be useful for the continued control of this pest. However, it appears that pre-existing cross-resistance to abamectin could facilitate the development of sbamedin resistance in some populations. Insecticide susceptibility is a resource, and these two new insecticides will need to be used with care in order to delay the evolution of resistance.

ACKNOWLEDGMENT

r thank N. Liu for technical assistance, F. Matsumura ror providing the CSMA strain. D. Cochran (or providing the Navy strain. and B. Zeichner (or providing the Dursban-R and CHL strains. I also thank B. Siegfried, D. Cochran. and one anonymous individual for their review or the manuscript. This study was supported in part by a grant from the U.S. Department of Agriculture and Hatch grant 139414.

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82 J. Agric. Entomol. Vol. 8, No.2 (1991)

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