Resistance, Cross-resistance and Chemical Control of Diamondback Moth in Taiwan: Recent Developments

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1 52 Resistance, Cross-resistance and Chemical Control of Diamondback Moth in Taiwan: Recent Developments E. Y. Cheng, Ching-hua Kao and Chi-sung Chiu Taiwan Agricultural Research Institute, Wufeng, Taichung, Taiwan, ROC Abstract Except for the chlorinated insecticides, all traditional insecticides and newly introduced IGR-type compounds have been investigated for their modes of action in respect to the resistance in diamondback moth, Plutella xylostella (L.) in Taiwan. Diamondback moth has a very active, efficient, and inducible mixed function oxidases (MFO) system/ complex, which is responsible for the high level of resistance to carbamates, synthetic pyrethroids, and benzoylphenyl urea. Sublines of MFOs respond quickly to the selection pressure of a new type insecticide when its molecular structure fits the substrate for one of the many MFOs. So far, four sublines of MFOs have been found which are responsible for the resistance to common carbamates, carbofuran, all synthetic pyrethroids and benzoylphenyl ureas. The MFO-type resistance in DBM is the worst resistance for insecticides since it would respond indefinitely and render the insecticide useless at any dosage. By investigating the genetic background of different sub-lines of MFOs, a strategy of resistance management has been proposed for benzoylphenyl ureas due to the highly recessive nature of its genes. The same strategy cannot be applied to common carbamates and carbofuran since the responsible MFOs were not recessive. Tactics and strategies of DBM resistance management implementation are collectively discussed. Introduction Taiwan Agricultural Research Institute (TARI) initiated a research program on insecticide resistant diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera:Yponomeutidae), in The purpose was to rationalize the control strategy of this pest for implementation. Since 1985, two reviews on the resistance, cross-resistance and chemical control of DBM were prepared from the available literature. In the first review, sampling method, geographic distribution of resistance, resistance induction, and cross-resistance were carefully evaluated (Cheng 1986). The second review covered DBM resistance information from other Asia regions (Cheng 1988), which clarified the cross-resistance profile of different insecticide categories and suggested countermeasures. Up to 1988, most needed information concerning DBM resistance to traditional insecticides was available. The failure of insect growth regulators (IGRs) and the success of new Bacillus thuringiensis Berliner products represented recent developments in Taiwan. We are now assembling available DBM resistance management tactics for implementation. 465

2 466 Cheng, Kao and Chiu IGR resistance In 1987, the benzoylphenyl urea (BPU)-type IGRs were introduced into Taiwan for DBM control, and the possibility of IGR resistance has been of great concern because of sporadic reports on the IGR resistance in DBM in Thailand (Cheng 1988; Vattanatangum 1988). The DBM seems to possess a natural mixed function oxidase (MFO) with metabolic activity toward diflubenzuron and triflumuron (Cheng et al. 1988b), and a mild teflubenzuron resistance was induced in DBM by laboratory selection (Perng et al. 1988). The MFO degradation serves as the resistance mechanism for IGRs in houseflies and DBM (Pimprikar and Georghiou 1977; Lin et al. 1989). In Taiwan, sensitivity of field collected DBM to chlorfluazuron and teflubenzuron was mostly below 10 ppm (medium lethal concentration [LC50) before 1987 (Cheng et al. 1988). However, the susceptibility of Lu-chu DBM to chlorfluazuron had changed from 3.8 ppm in March to 924 ppm in December 1988, a 243-fold increase in resistance ratio (Cheng et al. 1990). By the end of 1989, DBM collected from five locations showed varied chlorfluazuron resistance as the LC50s were ppm, while the sensitivities to teflubenzuron ranged from to ppm (Cheng et al. 1990). The IGR resistance observed in Taiwan DBM populations was significantly affected by the action of piperonyl butoxide. The synergistic ratios (S.R.) were in three DBM populations for teflubenzuron (Cheng et al. 1990), while the S.R. in five IGR-resistant DBMs ranged from 2.6 to 16.3 for chlorfluazuron. The DBM collected from the Lu-chu area in December 1988 had a high IGR resistance, but the resistance declined from and 243-fold to only 6.5- and 3.1-fold for teflubenzuron and chlorfluazuron, respectively, after 17 selectionfree generations (Cheng et al. 1990). The IGR resistance in DBM could be greatly reduced by crossing with the susceptible strain (Cheng et al. 1990). This genetic manipulation causes greater reduction in IGR resistance than incorporation of piperonyl butoxide in spray. Without further crossing for three more generations, the IGR resistance almost totally diminished in the offspring of RxS populations as the sensitivities to both teflubenzuron and chlorfluazuron were restored to that of the susceptible strain (Fig. 1), while the IGR selection-free F1-F7s of R-strain were still 78- and 20-fold more resistant to teflubenzuron and chlorfluazuron, respectively. The genetic expression of IGR resistance would be considered as highly recessive. By testing the backcross of F1 to the susceptible and resistant strains as well as the F2 offspring did not fit the suggested pattern of single gene control, which may be attributed to the heterozygosity of field-collected DBM used as the R-strain (Cheng et al. 1990). No evidence of sex-linked (Russell 1986) relationship in IGR resistance could be found in the reciprocal cross between susceptible and two IGR-resistant DBM strains (Cheng et al. 1990). Evaluation of new B. thuringiensis products In recent years, the improvement in B. thuringiensis efficacy has proceeded rapidly either by selecting mutants with higher potency or combining the B. thuringiensis toxins in a formulation (Moar et al. 1986, McGaughey and Johnson 1987; Padua et al. 1987; Gardner 1988; Morris 1988). For example, SAN415 was introduced in Taiwan in 1989 and its DBM control efficacy in the field was significantly better than other long-standing B. thuringiensis products (Chen 1990). Some newly developed B. thuringiensis products were evaluated against three long-standing products, Thuricide, Bactospeine and Dipel in the field on their efficacies on DBM (Kao et al. 1990). Bactospeine gave the poorest results with % control, while Thuricide provided % control. On the contrary, new B. thuringiensis products are much more effective on DBM. For example, control efficacies of CGA was 61.0% and Florbac FC and Florbac- XLV were 63.8 and %, respectively, while Bactospeine-XLV is an exception among new B. thuringiensis products with only minimum improvement in DBM control efficacy. The dosage used profoundly affected the control rate as the results of two CGA treatments indicated.

3 Insecticide Resistance in Taiwan 467 TEFLURENZURON-R R.R. = (PPM) GENERATlONS GENERATlONS Fig. I. The decline in resistance to teflubenzuron (a) and chlorfluazuron (b) accelerated by crossing with the susceptible-dbm LC50s for teflubenzuron and chlorfluazuron (averaged over three tests of F1 to F5 of SC-strain with addition of piperonyl butoxide) ranged from to ppm and 25 I.0 to ppm. respectively. LC50s for teflubenzuron and chlorfluazuron (averaged over 7 determinations of F59 to F77 of susceptible IL-strain) ranged from to 4.47 ppm and 8.32 to I.68 ppm, respectively. Experimental chemicals A. Diafenthiuron (Polo R) A synthetic insecticide, diafenthiuron, gave extremely good control of both DBM and Spodoptera litura. The soluble concentrate (SC) formulation of diafenthiuron performed equally well for both pest species, while the wettable powder (WP) formulation was better on DBM than on S. litura (Kao et al. 1990). Diafenthiuron provided better and more stable control when compared to B. thuringiensis products. Since diafenthiuron was extremely effective against DBM in the field, its toxicity to both the susceptible and resistant DBM was further compared in the laboratory. Results showed that the multiple-resistant DBM had the same susceptibility (LC50) to diafenthiuron as the susceptible strain, i.e. 245 ppm (Table 1), therefore, there is no crossresistance from existing insecticides. The addition of piperonyl butoxide to diafenthiuron spray Table I. The susceptibility and synergistic tests of diafenthiuron on DBM for possible crossresistance from other insecticides. Insecticides or combinations LC50 (ppm) R.R. and S.R. Suscep. strain Resist. straina Diafenthiuron R.R. = I Diafenthiuron + piperonyl butoxide S.R. = I (1 :5) Resistant SC-strain (Cheng et al. 1990). Resistance ratio and synergistic ratio.

4 468 Cheng, Kao and Chiu caused no difference, demonstrating that diafenthiuron is not affected by the inherited and induced oxidative metabolism in DBM. Tridiphane (2-(3, 5-dichlorophenyl)-2-(2, 2, 2-trichloroethyl]oxirane, TDP) It has been found that TDP can increase atrazine toxicity to weeds. Zorner and Olson (1981) showed that TDP inhibited atrazine metabolism in giant foxtail, and their preliminary data also indicated that TDP inhibited enzymatic conjugation of atrazine with GSTase. Similar synergistic effects of TDP on insecticides was observed in insects (Lamoureux and Rusness 1987). Diazinon metabolism in the housefly was inhibited by either or both TDP and S-(tridiphane) GSH and this was probably the cause of synergism of diazinon. By incorporating tridiphane as the synergist, approximately 2-fold increase in synergistic ratio for some OP insecticides was obtained in both the susceptible and resistant DBM strains (Tables 2 and 3). Since the action of TDP is so far not specific to R-strain, the role of GSTase in OP-resistance has not been confirmed, but the utilization of TDP in practical spray is worth investigating. Table 2. The synergistic effect of TDP on two organophosphorus compounds in susceptible and resistant DBMs. Insecticides TDP synergistic ratio Susc. R1ª R2 R3 Mevinphos I I.7 Profenofos 1.3 I I.8 ªR1, R2. R3 are three resistant strains. Table 3. Synergistic ratios of TDP to several OPs in a resistant DBM strain. Insecticides TDP synergistic ratio Mevinphos I.7 Profenofos I.8 Methidathion I.6 Quinalphos > 2.0 Phenthoate I.6 Parathion 1.8 Methamidophos I.0 Diazinon I.0 Mephosfolan I.0 1. MFO resistance Update of DBM Resistance Mechanisms Resistance characteristics of DBM to different insecticides were extensively reviewed by Cheng (1988). With the additional information of IGR-resistance, oxidative metabolism obviously emerged as the most important detoxication mechanism in DBM. Chou and Cheng (1983) first noticed that DBM can develop carbofuran resistance, which acted independently from resistances of carbaryl, methomyl, synthetic pyrethroids and other insecticides. Hence, in the first International DBM Workshop, we objected to the term carbamate resistance being used in connection with DBM. To settle the argument, Cheng et al. (1986) demonstrated the specificity of MFOs for different insecticides. New lines of MFO for metabolizing IGRs again confirmed the diversity of MFOs in DBM. We have now concluded that MFO is a single and

5 Insecticide Resistance in Taiwan 469 most important biochemical complex for the resistance problem in DBM. From the investigation of carbamates, synthetic pyrethroids. IGRs and other experimental insecticides, the characters of MFO resistance in DAM are outlined as follows: (1) Naturally inherited MFO constituted the tolerance/resistance of DBM to certain insecticides such as carbaryl, methomyl and propoxur; (2) MFO resistance to carbofuran, synthetic pyrethroids and IGRs are inducible; (3) MFO possess a high diversity for different xenobiotics including experimental insecticides still being developed; (4) MFOs are either specific for a single compound. for example, carbofuran, or a chemical group, i.e. synthetic pyrethroids; and (5) MFOs arc genetically diverse. i.e. highly recessive for IGRs and intermediate for synthetic pyrethroids and carbofuran. while inheritable for carbaryl methomyl and propoxur. All these facts indicate that DBM has a very efficient, active and either inherited or inducible MFO complex. Once a xenobiotic molecule fits the substrate for one of the many hidden MFOs, DBM with this subline MFO would survive and propagate under the selection pressure. Hence a new type of MFO resistance appears. One general character of MFO-based resistance is that it would respond indefinitely in amplitude and eventually render the control chemical useless at any dosage. Carbaryl. methomyl, carbofuran, synthetic pyrethroids and IGRs have all met the same fare. 2. Glutathione-S-transferase involvement in organophosphorus resistance Organophosphorus (OP) insecticide is one exception to the detoxication of MFO, and the OP resistance in DBM is multifactorial as described by Cheng (1988). Although the role of glutathione-s-transferase (GSTase) has been a controversial subject (Kao et al. 1989), the synergistic effect of tridiphane on mevinphos, profenofos, quinalphos, methidathion, phenthoate and parathion (Tables 2 and 3) provide positive evidence of GSTase involvement in the metabolism of OP insecticides; the OP-resistant DBM possessed higher GSTase activity (Cheng et al. 1983). Whether this detoxication is universal or specific is still under investigation. 3. A summation of important mechanisms in DBM insecticide resistance The summation of important mechanisms are listed in Table 4. Resistance profile Stability Genetic expression Table 4. Important mechanisms in DBM insecticide resistance OPs Carbaryl, methomyl Carbofuran Synthetic IGRs Cartap and propoxur stable to unstable intermediate Resistance mechanism multifactorial involved Responsi ble insensitivity AChE biochemical GSTase entitle, carboxylesterase esterase Practical synergist TDP stable unstable unstable very unstable stable dominate or intermediate intermediate recessive additive inherited (proposed) monofactorial monofactorial monofactorial monolactorial monofactorial (proposed) MFOn MFOc MFOs MFOi broad spectrum esterase (proposed) piperonyl piperonyl piperonyl piperonyl butoxide butoxide butoxide butoxide

6 470 Cheng, Kao and Chiu Table 4. Continued. Re Resistance amplitude medium high high Comments for field OPs with unsta- Not recom- Not reusage ble resistance mended for commended are useful in use on for used on insecticide crucifers; fast-growing alternation pro- crucifers; gram occasionally used in early stage of crucifer to avoid residue problem amfoa, MFOc, MFOr and MFOi are different sublines of MFO high Strongly recommended for use in crucifers to control pests other than DBM high Can be used in a mosaic or alternation spraying program (still under development) mild Recommended for use in an insecticidealternation program except in seasons with high precipitation or dews due to its high water-solubility Proposed Tactics for DBM Resistance Management 1. Resistance monitoring Since the use of insecticides for crucifers is unavoidable in Taiwan, the resistance monitoring becomes essential for constructing and implementing a rational DBM resistance management program. Currently, the DBM resistance to insecticides is monitored by the method developed by Cheng (1981), and the result is reliable and satisfactory although it is laborious and lengthy. A simpler leaf dipping method is under development for the large-scale resistance monitoring program. Insecticide solutions at 0.75-, 1- and 2-fold levels of the recommended dosages are used for dipping, and the mortality observations are set at 24, 48 or up to 120 hours for different insect: :ides. The result will either verify the efficacy of recommended dosage or indicate possible development of resistance to an insecticide. 2. Genetic dilution The idea of using genetic dilution to combat resistance had been raised in a previous review (Cheng 1988). Resistance reduction by genetic dilution had been clearly demonstrated for carbofuran, fenvalerate and IGRs, and sometimes is more effective than the incorporation of synergist in spray. By utilizing the genetic dilution principle, two approaches, i.e., insecticide alternation and mosaic spray, are practical and possible. A. Alternation of insecticides: Chemical insecticides should be alternated between groups with no or minimum cross-resistance as we recommended previously (Cheng 1988), and alternated with microbial insecticide such as B. thuringiensis. The reintroduction of any synthetic insecticide should be based on the results of resistance monitoring. B. Mosaic spray management (proposed): The BPU-type IGR resistance in DBM is recessive and independent from other resistances. The IGR resistance of DBM in the field may be manageable if a sanctuary could be provided to harbor a portion of the DBM population free from the IGR selection. By mosaic spraying of IGR and B. thuringiensis in alternate rows, the dominant IGR-susceptible gene can be preserved in the field population. Genetic dilution would occur when the survivors of two different treatments mated, thus preventing or delaying IGR resistance. The proposed sanctuary in a mosaic spray should be designed in a way to provide maximum mixing for DBM adults, which in turn may depend on factors such as rate of dispersal.

7 Insecticide Resistance in Taiwan 47 1 The applicability of this strategy is currently being tested. Theoretically, mosaic sprays of IGRs and B. thuringiensis is desirable to minimize the possibility of producing cross-resistance, and both treatments also favor the survival of natural enemies. Preservation of natural enemies, sanctuaries for the dominant susceptible gene, and two insecticides free from cross-resistance should be considered as the most favorable combinations in an integrated pest management (IPM) scheme. If the IGR resistance continues to develop slowly in mosaic sprays of IGRs and B. thuringiensis, an insecticide such as mevinphos which causes only short-lived resistance (Cheng et al. 1985) can substitute as the control measure for a period of time to relieve the IGR selection. Two requirements are needed to conduct the mosaic spraying: (1) the farmers should be well educated and (2) the resistance should be closely monitored so that the needed adjustment can be made in time. 3. Synergists Three major chemical groups of insecticides encountered oxidative metabolic resistance from at least four sublines of MFO. There are many synergists to counter the oxidative metabolism, and piperonyl butoxide is already in commercial use. The consequence of utilizing piperonyl butoxide to counter the resistance has not been fully evaluated in DBM, which can also become resistant to piperonyl butoxide (Chen and Sun 1986). For some OP insecticides, the incorporation of tridiphane (TDP) resulted in a two-fold increase in control efficacy by inhibiting GSTase activity. It is still unclear how specific this synergist is to the OP resistance and physiological degradation. Some OP insecticides are still used in the alternation to manage the resistance, and the incorporation of this synergist in practice is worth consideration. 4. Natural enemies Although the importance of parasitic wasps had been ignored before, their continual presence in cabbage fields still constitutes a natural mortality factor for DBM despite the heavy insecticide spray. Serious biological/ecological information gathering and the modelling between DBM and natural enemies are needed for an integrated resistance management program (IRMP). Besides, screening insecticides with minimum impact on natural enemies is also needed. 5. Farmers education and participation Farmers education has nothing to do with the basic DBM resistance research, but is vital in implementing a DBM resistance management program. From the past experience, the traditional field demonstration tactic is a failure due to the free market practice of agrochemicals in Taiwan, which allowed farmers to receive both accurate and inaccurate information. The one pest, one chemical, one field and one morning demonstration session resulted in only minimal farmer involvement, and also was not realistic in dealing with the multiple pest situation of cruciferous fields. A complete diagnosis of field pest problems, followed by proper recommendations to control DBM and other pests, are essential to gain the farmers acceptance in future implementation programs. In other words, the extension agency cannot conduct a DBM resistance management program without incorporating the solutions for other important pests. Educational materials should also be aimed to protect the crucifers rather than to manage the DBM resistance only. It is also best to include the disease control information. Farmer participation is another important element. Multiseasonal participation is needed, and the aim is to encourage the participating farmers to be future field instructors for others.

8 472 Cheng, Kao and Chiu Constraints in DBM Resistance Management The management of DBM resistance depends on rational and orderly use of insecticides, which usually is not possible since farmers use various insecticides to control other insect pests, thus interfering with DBM resistance management. Geographical and seasonal differences in crop growth and pest abundance will affect the resistance management details. Price fluctuations and the quality demands for vegetables seriously affect the farmer s commitment to IRMP. The health hazard of pesticides to both farmers and consumers limits the insecticide selection and alternation. Proposed DBM Resistance Management Strategy Based on the above tactics and constraints, TARI has constructed a tentative strategy for the management of cruciferous pests with emphasis on DBM. This program which will last from July 1990 to June 1993, is carried out at two locations: Ten-chung and Pei-tou, with participation of six farms. It involves the following: Monitoring the insecticide resistance in DBM. Insecticides screened were: a. Permethrin (one synthetic pyrethroid is enough due to the cross resistance within the group). b. Mevinphos, profenofos, methidathion, actellic (other OP compounds are not recommended due to their stable resistance). c. Carbofuran (DBM has inherited tolerance to other carbamates). d. Cartap. e. Chlorfluazuron and teflubenzuron. After analyzing the screening results, mevinphos (633 ppm) and cartap (833 ppm) were chosen in the insecticide alternation program. Incorporating the newly developed B. thuringiensis: SAN 415 which is more effective than older products and acceptable to farmers is used. Its use can reduce the selection pressure of chemical insecticides. Selecting proper insecticides for controlling other important cruciferous pests: Bifenthrin (28 /ppm) is chosen to control Spodoptera litura, S. exigua, Trichoplusia ni and P. rapae. By combining the data from these three activities, an IRMP for cruciferous pests, with emphasis on DBM resistance, is constructed. Mevinphos, cartap, SAN 415 and bifenthrin were provided to six participating farmers for field comparison with their own control practices. Spray details were recorded for IRMP program analysis. No insect count is needed since the degree of satisfaction of farmers on their vegetable quality is of most concern. The discussion session is held once a month between farmers and researchers. Establishing the residue monitoring system. Less-educated farmers may ignore the safety aspects and use pesticides shortly before harvesting, hence residue control is needed. In Taiwan, we have established pesticide residue rapid bioassay stations in more than 40 farmers associations and wholesale markets to detect pesticide residues on vegetables (Chiu et al. 1991), and one station has participated in this program.

9 Insecticide Resistance in Taiwan 473 Field demonstration and implementation. The recommended IRMPs are conducted and constantly improved in experimental fields on a year-round basis for 3 years. Educational sessions for the participating farmers are held every 30 days to discuss not only the DBM but also the identification and control technologies of other pests as well. Currently, the four-insecticides package recommended in Ten-chung and Pei-tou experimental sites have received most favorable response, and the program will expand from 6 to 70 farmers in One advantage of this practical training is to keep the farmers away from the influence of profit-oriented agrochemical retailers who have been playing a major role in incorrect pesticide usage in Taiwan. Other farmer associations have easy access to inspect the IRMP experimental fields and can have discussions with the participating farmers at any time. Any interested farmer can start the IRMP practice with instruction from the extension service of a Farmers Association or from existing IRMP participating farmers. Recent R and D for DBM Resistance Management Two important scientific disciplines, genetics and biochemistry, have been brought together at TARI. 1. Selecting homozygous resistant strains for various insecticides: The OP insecticides are important in DBM resistance management programs since some of them are recommended in the alternation list. Since OP resistance is multifactorial, selection of genetically pure lines (monofactorial in biochemistry) with only one resistance mechanism hopefully will help to clarify the importance of individual mechanisms. The selection has been underway for more than a year now at TARI and the selection is quite successful. Similar progress has been obtained for carbofuran-resistant strain selection. However, the selection for synthetic pyrethroids and IGR-resistant strains was extremely difficult due to their recessive genetic nature. The overall results of various selections are similar to previous laboratory selections from the susceptible strain (Cheng et al and 1988b; Chou and Cheng 1983). 2. Clarifying responsible biochemical entities, and developing biochemical detection kits for resistance: Biochemistry is fundamental to the study of toxicology, resistance mechanisms and the action of synergists, etc. A better understanding of the biochemical reaction will not only help to identify the resistance mechanism and sort out relationships of crossresistance, but also facilitate the development of a rapid detection kit for resistance in the field. So far, the possible entities involved in DBM resistance are acetylcholinesterase, carboxylesterase, GSTase, MFOs, etc. Among them, GSTase has been a research subject in TARI for the past few years, and the effort has been concentrated on the purification and identification of various GSTase isozymes. Affinity chromatography has been used successfully to purify a major GSTase (Cheng et al. 1988a), two to three minor GSTases have been subsequently isolated by electrophoresis, and immunological investigation of GSTases has been initiated as well. AChE insensitivity test for different OP insecticides has also been initiated according to the method of Moores et al. (1988). References Chen, J. S., and Sun, C. N Resistance of diamondback moth (Lepidoptera:Plutellidae) to a combination of fenvalerate and piperonyl butoxide. J. Econ. Entomol., 79, Chen, W. S Annual report on COA Project of the Management of Diamondback Moth. Tainan District Agricultural Improvement Station, Tainan, Taiwan, ROC (in Chinese). Cheng, E. Y Insecticide resistance study in Plutella xylostella L. I. Developing a sampling method for surveying. J. Agric. Res. China, 30,

10 474 Cheng, Kao and Chiu Cheng, E. Y The resistance, cross resistance and chemical control of diamondback moth, In Talekar, N. S., and Griggs, T. D. (ed.) Diamondback Moth Management: Proceedings of the First International Workshop, Asian Vegetable Research and Development Center, Shanhua, Taiwan, Problems of control of insecticide-resistant Plutella xylostella. Pestic. Sci., 23, Cheng, E. Y., Chou, T. M., and Kao, C. H Insecticide resistance study in Plutella xylostella L. IV. The activities of glutathione-s-transferase in organophosphorus-resistant strains. J. Agric. Res. China, 33, Insecticide resistance study in Plutella xylostella L. VI. An experimental analysis of organophosphorus and synthetic pyrethroid resistance. J. Agric. Res. China, 34, Cheng, E. Y., Kao, C. H., and Chiu, C. S Insecticide resistance study in Plutella xylostella L. X. The IGR-resistance and the possible management strategy. J. Agric. Res. China, 39, Cheng, E. Y., Kao, C. H., and Tsai, T. C Insecticide resistance study in Plutella xylostella (L.) VIII. The specificity of oxidative detoxication mechanism in larval stage. J. Agric. Res. China, 35, Cheng, E. Y., Lin, D. F., Chiu, C. S., and Kao, C. H. 1988a. Purification and characterization of glutathione-s-transferase from diamondback moth, Plutella xylostella L. J. Agric. Res. China, 37, Cheng, E. Y., Lin, D. F., Tsai, T. C., and Kao, C. H. 1988b. Insecticide resistance study in Plutella xylostella L. IX. The selective metabolism of insecticides. J. Agric. Res. China, 37, Chiu, C. S., Kao, C. H., and Cheng, E. Y Rapid bioassay of pesticides residues (RBPR) on fruits and vegetable. J. Agric. Res. China, 40, Chou, T. M., and Cheng, E. Y Insecticide resistance study in Plutella xylostella The insecticide susceptibilities and resistance response of a native susceptible strain. J. Agric. Res. China, 32, Gardner, W. G Enhanced activity of selected combinations of Bacillus thuringiensis and beta-exotoxin against fall armyworm (Lepidoptera: Noctuidae) larvae. J. Econ. Entomol., 81, Kao, C. H., Chiu, C. S., and Cheng, E. Y Field evaluation of microbial and chemical insecticides for diamondback moth and other lepidopterous pests control on cabbage. J. Agric. Res. China, 39, Kao, C. H., Hung, C. F. and Sun, C. N Parathion and methyl parathion resistance in diamondback moth (Lepidoptera:Plutellidae) larvae. J. Econ. Entomol., 82, Lamoureux, G. L., and Rusness, D. G Synergism of diazinon toxicity and inhibition of diazinon metabolism in the house fly by tridiphane: inhibition of glutathione S-transferase activity. Pestic. Biochem. Physiol., 27, Lin, J. G., Hung, C. F., Sun, C. N Teflubenzuron resistance and microsomal monooxygenases in larvae of the diamondback moth. Pestic. Biochem. Physiol., 35, McGaughey, Wee, H., and Johnson, D. E Toxicity of different serotypes and toxins of Bacillus thuringiensis to resistant and susceptible indian-meal moth (Lepidoptera: Pyralidae). J. Econ. Entomol., 80, Moar, W. J., Osbrink, W. L. A., and Trumble, J. T Potentiation of Bacillus thuringiensis var. kurstaki with Thuringiensin on beet armyworm (Lepidoptera: Noctuidae). J. Econ. Entomol., 79, Moores, G. D., Devonshire, A. L., and Denholm, I A microplate assay for characterizing insensitive acetylcholinesterase genotypes of insecticide-resistant insects. Bull. Entomol. Res., 78, Morris, 0. N Comparative toxicity of delta-endotoxin and Thuringiensin of Bacillus thuringiensis and mixtures of the two for the bertha armtworm (Lepidoptera:Noctuidae). J. Econ. Entomol., 81,

11 Insecticide Resistance in Taiwan 475 Padua, L. E., Ebora, R. V., and Moran, D. G Screening of Bacillus thuringiensis against Asiatic corn borer, Ostrinia furnacalis (Guenee) and diamondback moth, Plutella xylostella (L.). FFTC Technical Bulletin No. 103, Taipei, Taiwan, ROC. 7 p. Perng, F. S., Yao, M. C., Hung, C. F., and Sun, C. N Teflubenzuron resistance in diamondback moth (Lepidoptera: Plutellidae). J. Econ. Entomol., 81, Pimprikar, G. D., and Georghiou, G. P Mechanisms of resistance to diflubenzuron in the house fly, Musca domestica (L.). Pestic. Biochem. Physiol., 12, Russell, P. J Genetics. Boston: Little, Brown and Company, Vattanatangum, A Recent problems on chemical control of Thailand agricultural insect pests related to insecticide resistance of diamondback moth and other major species. Report Meeting of the Joint Research Project: Insect Toxicological Studies on Resistance and Integrated Control of the Diamondback Moth. Department of Agriculture, Thailand, Zorner, P. S., and Olson, G. L The effect of Dowco 356 on atrazine metabolism in giant foxtail. In Proceedings of the North Central Weed Control Conference, Abstract, Vol. 36, 115.