Spodoptera frugiperda (J. E. Smith is a genus of Lepidoptera Noctuidae, Spodoptera, also known as autumn armyworm, originated in the Americas and is one of the main pests of maize production and one of the most destructive corn crop pests in Brazilian history. Its larvae feed on a variety of plants, which can harm corn, rice, sorghum, millet, sugarcane, vegetable crops and cotton, etc., and if not controlled in time, may cause significant yield losses. The insect is prone to generational overlap and has strong adaptability and migration capacity, which allows it to erupt in any area where conditions are suitable. There are two ecological typings associated with the host: the maize-type grassland moth prefers to feed on maize and sorghum, while the rice type prefers to eat rice. This difference is not limited to their preference for hosts, but also extends to their physiology, mating behavior, and sensitivity to pesticides.
Since 1996, the cultivation of genetically modified crops that express bacillus thuringiensis (Bt) insecticidal proteins has been promoted around the world for the control of lepidoptera pests, of which the grassland nightcrawler is one of the main control objects. However, the development of field resistance to the Bt protein by the grassland moth has threatened the sustainable use of trans-Bt crops. From 2010 to 2018, several papers have reported the field resistance of the grassland moth to the conversion of Cry1F, Cry1Ab, Cry2A and Vip3A gene crops, indicating that relying on trans-Bt crops alone is not enough to control the pest.
As an invasive alien species, the grassland nightcrawler entered Yunnan Province, China in January 2019, and has since been affected in Guangxi, Guizhou, Guangdong and Hunan, and has now spread to Anhui, China's main grain producing province. Due to the control of chemical pesticides and biopesticides in many countries, the specific resistance status of these invading Chinese grassland moths is still unclear, based on this, it is urgent to carry out a series of scientific and effective resistance monitoring and resistance mechanism studies for grassland moths. In 2019, Li Yongping and Cui Li discussed the current situation of drug resistance and chemical control technology of grassland nightcrawler, from the aspects of drug resistance and cross resistance, population genetics and key technologies of chemical control, which provided theoretical support for the chemical control of grassland nightcrawler in a timely manner. In this paper, we intend to review the history of the development of resistance monitoring of grassland moth and the progress of resistance mechanism research, in order to provide a reference for the current field control of grassland moth in China and the early implementation of its resistance monitoring and research.
1
Development of resistance to pesticides by the grassland moth
The keywords "fall armyworm" and "resistance" were searched in the PubMed literature database, and a total of 172 articles were retrieved, and from the statistical analysis from 1975 to 2016, the reports of drug resistance of the grassland moth showed a year-on-year trend (Figure 1). Taken together, the degree of dependence on insecticides and the frequency of use in different regions have led to different levels of resistance of the grassland moth in different regions. Before the transfer of Bt corn to promote planting, chemical control has been the main distribution of the grassland moth in the countries and regions such as the United States and Brazil and other necessary control methods, commonly used agents are mainly traditional organophosphorus, carbamates and pyrethroid insecticides, and its resistance to insecticides is also mainly concentrated in the above 3 types of agents, and the resistance occurrence areas are mostly concentrated in Florida, Puerto Rico and Mexico, Brazil and other places. In addition, there have been few reports of resistance of the grassland moth to amide insecticides such as chlorhexabenamide and flubenzamide.
Figure 1 Articles reported on resistance of the grassland moth from 1975 to 2016 in PubMed
1.1 Resistance of the grassland moth to organophosphorus insecticides
In the 1970s, organophosphorus pesticides began to be used as an alternative to DDT for the control of pests in the field. In 1981, Wood et al. reported the resistance of the nocturnal moth to methyl parathion (113 times) and enemy insects (trichlorfon, 31 times) in the Hammond area of the United States. In 1991, Yu et al. reported that compared with sensitive laboratory populations, the grassland moth in the corn field of northern Florida in the United States developed different degrees of resistance to commonly used organophosphorus insecticides, among which chlorpyrifos, methyl parathion, diazinphos (diazinon), methylpropiophos (sulprofos), Dichlorvos and malathion had medium to high resistance levels ranging from 12 to 271 times in the field; in 2003, they found that the resistance of the grassland moth collected from the Stella region of Florida to methyl parathion was as high as 354; and by 2007, the resistance level of the grassland moth to methyl parathion was reduced in the northern Florida cities of Gainesville and Stella. 30x and 39x, respectively. A 2019 study by Gutiérrez-Moreno et al. showed that the meadow moth in Sonora, Mexico, was 20 times more resistant to chlorpyrifos, while various puertorier populations had a 47 multiple of resistance, with higher resistance levels than Mexican populations.
The above development dynamics of the resistance of the grassland moth to organophosphorus insecticides can be taken as an example of methyl parathion, in the Stella region of Florida, where the grassland moth has developed high resistance to methyl parathion (354 times), other agents are used for control, and its resistance to methyl parathion is significantly reduced (39 times) after 3 years. At the same time, according to resistance monitoring reports, the grass moth has maintained a moderate resistance level (20 to 25 times) to chlorpyrifos. Therefore, in the drug strategy, it is necessary to pay attention to preventing the high resistance risk of the grassland night moth to chlorpyrifos and methyl parathion, and measures such as scientific discontinuation and rotation of drugs should be taken.
1.2 Resistance of the grassland moth to carbamate insecticides
Since Young et al. first reported in 1979 that the grass moth developed a moderate level of resistance to carbaryl in Georgia, the resistance of the grassland moth to carbaryl has been continuously reported. For example, Wood et al. reported in 1981 that the grassland moth in the Hammond area of the United States had 41 times the resistance to naphthalix; in 1991, Carpenter et al. monitored that the meadow moth on maize in Gil County, Florida, usa, produced a low level of resistance of 4.25 times to methomyl; in 1997, Adamczyk et al. monitored the resistance of the grassland moth in Louisiana, USA, and found that the grass moth harvested from pasture and corn was still more sensitive to antidovir, and the resistance multiple was between 0.01 and 1.97; in 1991, Yu et al. monitored the population of the grassland moth in the Gainesville area of Florida and found that its resistance to carbamate insecticides was between 14 and 192 , where resistance to thiodicarb and indovir was 26.1, respectively and 14.4 times, the resistance multiple to menavir is greater than 192; in 2003, Yu et al. monitored the resistance of the grass moth on the corn in the Sitrah area of Florida and found that its resistance to the methylnaphthalix was as high as 562 times; in 2007, they monitored two populations of the nocturnal moth collected from northern Florida (Gainesville and Sitra) and found that their resistance to naphthalax reached 1,159 times and 626 times, respectively. Comparing the above reports, it is found that from 1991 to 2007, the resistance of the grassland moth to naphthalix in the Gainves area of Florida increased by 6.04 times, an average of 0.38 times per year; between 2003 and 2007, The resistance of the grassland moth to mesnaphrine in the Citra region of the United States also increased by 1.11 times, an average of 0.28 times per year; the latest monitoring data in 2019 showed that the resistance multiples of the grassland moth to antidovir and sulfur suzephine in various regions of the United States were 223 and 124, respectively, and the resistance levels of high resistance had reached high resistance.
According to the above monitoring reports on the resistance of grassland moth to carbamate insecticides, the resistance of grassland moth to methylnaphthalix is the most prominent in the northern florida region of the United States, and since the first report in 1979, the grass moth has a moderate level of resistance to meranyl, and continued until 2007, the field resistance of the American grassland moth to meranyl has reached a peak, such as the field resistance of the grassland moth in the Gainves area is as high as 1,159 times. In addition, monitoring results showed that the grassland moth was capable of developing high levels of resistance to the traditional carbamate insecticides dodoviride and thioses. Therefore, when using such insecticides to control the grassland moth, the effective control dose should be clarified to avoid loss of crop quality and yield. At the same time, it can be seen from the development of resistance of carbamate insecticides in the United States that there are obvious differences in the development of resistance in the field in different regions, which may be mainly related to the local drug background.
1.3 Resistance of the grassland moth to pyrethroid insecticides
Pyrethroid pesticides appeared in the early 1980s, and by virtue of their wide insecticidal spectrum, high control efficiency and low toxicity, they quickly became the preferred agent for the control of agricultural pests, and played an important role in the control of grassland moth. However, with the promotion and application of pyrethroid insecticides in the field, their resistance problems have become increasingly prominent. Since Wood et al. first reported in 1981 that the grassland moth in hammond area of the United States had a 17-fold resistance to permethrin, in 1991, Yu et al. reported the monitoring results of the resistance of the corn field nocturnal moth to eight commonly used pyrethroid insecticides in northern Florida, including permethrin (13.9 times), cypermethrin (cypermethrin, 5.6 times), cypermethrin (cyhalothrin, cypermethrin, cypermethrin, cyhalothrin, cypermethrin, cypermethrin, cyperthrin, cyhalothrin, cypermethrin, cypermethrin, cyhalothrin, cypermethrin, cypermethrin, cypermethrin, 12.5 times), fenvalerate (1.7 times), tetrabromothrin (tralomethrin, 41.2 times), bifenthrin (29.4 times), tetramethrin (4.6 times) and fluvalinate (fluvalinate, 216 times). The results showed that the resistance level of the grassland moth to pyrethroid insecticides was between 2 and 216 times, respectively, of which the resistance to cypermethrin was the highest, and the resistance to cypermethrin remained the highest, while the sensitivity to cypermethrin remained. In 1997, Adamczyk et al. compared the sensitivity differences of field grassland moth populations collected from pasture and maize to highly efficient cypermethrin, and found that its resistance multiple was between 0.40 and 3.07, and the resistance of the maize field nocturnal moth was higher than that on the pasture. In 2013, the Mexican grassland moth population with the highest proportion of resistance was reported to have a resistance multiple of 19 permethrin, while the Mexican population of nocturnal moth collected at the same site in 2015 had lower resistance to permethrin (3 times).
In summary, it can be seen that the sensitivity of grassland moths feeding on different hosts in the same country and region is also different, so the resistance dynamics of grassland moths on different hosts should be monitored in a timely manner to provide a scientific basis for the selection of efficient and low-cost insecticides for field control.
1.4 Status of resistance of the nocturnal moth to other types of pesticides
As of 2017, the grassland moth in the Americas has developed resistance to at least 29 insecticides, including the chemical insecticides carbamates (subgroup 1A), organophosphorus (subgroup 1B), pyrethroids (group 3), and Bacillus thuringiensis Cry1F protein, which have a known mechanism of action. Huang et al.'s article pointed out that under the resistance management strategy of high doses combined with shelters in North America, 15 years after the use of Bt genetically modified crops to control Lepidoptera pests, some areas have detected the resistance of some target pests to Bt in the field, such as the grassland moth in Puerto Rico in the United States, the African stem borer Busseola fusca in South Africa, and the cotton red boll worm Petinophora gossypiella in India. For areas where Bt-resistant grassland moth has emerged, it is necessary to combine the use of insecticides of different mechanisms of action for control, so the problem of the interaction between the resistance of the grassland moth to Bt and its resistance to other pesticides is worthy of attention, according to Zhu Equal's 2015 report, the anti-Bt grass moth has a 19-fold cross resistance to acephataphos (acephate).
Belay et al. reported in 2012 that chlorantraniliprole, flubendiamide, polycycline (spinosad), ethyl polybactericide (spinetoram), and ethyl polybactericide (spinetoram) were used in the Santa Isabel area of Puerto Rico, usa. Agents such as indoxacarb and methoxyfenozide can effectively control the grassland moth. However, after only 6 years, Gutiérrez-Moreno et al. found in 2018 that the population of the Nocturnal Moth in the field of Puerto Rico in the United States has developed high levels of resistance to a variety of novel mechanisms of action insecticides, such as fluorobenzamide (500 times) and chlorantraniliprostamide (160 times), and moderate resistance to ethyl polybactericide (14 times), in addition to polycycide (8 times), methylamectin benzoate (emamectin benzoate, Abbreviated methylvidine salts, 7 times) and avermectin (abamectin, 7 times) are in the low level of resistance stage.
Chlorantraniliprox benzamide is a new generation of biamide insecticide developed by DuPont in the United States, which over-releases calcium ions stored in cells by activating insect fish nittin receptors, resulting in insect muscle contraction, incapacitation, and then death. The latest findings in 2019 show that the high level of resistance of the grassland moth to chlorpyrifosan benzamide (160 times) and flufluprone (500 times) has been monitored in parts of Puerto Rico in the United States; in the same year, Bolzan et al. found that there are different degrees of interaction resistance between the chlorine-resistant benzamide grass moth population (237 times) and other amide insecticides in parts of Puerto Rica, of which there is a low level of interaction resistance with bromocyanidamide (27 times), while there is up to 42% with fluorophenyl amide. 000 times the cross-resistance, so high attention should be paid to preventing the field resistance of the grassland moth to diamide insecticides.
In 2018, FAO officially reported the invasion of the grassland moth into the entire African continent. According to the latest sensitivity studies in Africa, the use of different commercial preparations at recommended field doses, chlorantranose benzamide, ethyl polybactericide and polycycidecin can be effective in the control of grassland nocturnal moth, but the 48-hour fatality rate of 85% methylnaphalox wettable powder (2 kg/hm2) and 50% malathion emulsion emulsion (2 L/hm2) is very low, only 13.9% and 32.8%, respectively, which is consistent with the above report that the grassland nocturnal moth has developed a high level of resistance to methylnaphalact and organophosphorus insecticides.
The above reports show that the grass moth also developed moderate to high levels of resistance to insecticides of some novel mechanisms of action, and its sensitivity baseline was very low, taking the sensitivity baseline of chloranthropite benzamide and fluorobendanamide as an example, its LD50 values were 0.001 and 0.003 μg/head, respectively. Therefore, with the deepening of the invasion of grassland moth, it is necessary to accelerate the study and establish a baseline of sensitivity to commonly used insecticides, and monitor the evolution of resistance of grassland moth in China as soon as possible to provide data support for its scientific and effective control.
2
Mechanism of resistance of the grass moth
The development of pest resistance is often related to the continuous pressure of field agent selection and the biological characteristics of the pest itself. Since the resistance of the grassland moth to mesnaphthalis was first reported in 1979, the research on the mechanism of resistance to the grass moth has increased year by year. At present, it is generally believed that the resistance mechanism of grassland moth to insecticides mainly includes the following three aspects: reduced epidermal penetration, enhanced detoxification effect and decreased target sensitivity, of which enhanced metabolic detoxification and decreased target sensitivity are the main mechanisms leading to the resistance of grassland moth to insecticides.
Mccord et al. studied the physiological mechanism of resistance of the grassland moth to methylnaphrine as early as 1987, and found that piperonyl butoxide (PBO) can reduce the resistance level of the grassland moth to methylnaphrine from 90 times to 6 times, and the synergistic effect is significant, indicating that cytochrome P450 multifunctional oxidase (P450s) may play a major role in the production of resistance. At the same time, ex vivo metabolic studies have shown that the oxidation and metabolism of methylnaphthalene in the resistant population is 5 times that of the sensitive population. In addition, epidermal penetration studies using 14C-labeled menaphalax showed that after 24 h of drip treatment, the penetration rate of the larval larvae of methylnaphane adversarial populations was only 45%, while the penetration rate of sensitive populations could reach 68%. It was revealed that the high resistance of the grassland moth to mefenacea was mainly formed by the two partial mechanisms of reduced epidermal penetration and enhanced oxidative metabolism (through hydroxylation and epoxidization).
Dumas et al. found in 1990 through baculovirus-mediated research that the phosphotriesterase (OPD) protein expressed in vivo can significantly improve the hydrolytic metabolism of paraoxon (paraoxon) of the grassland moth, and increase its resistance by 280 times, indicating that the enhancement of esterase hydrolytic metabolism is the main mechanism of the resistance of the grassland moth to paraoxon. Yu et al. (1996) found that the detoxification enzyme activity of the field population of the grassland moth was significantly increased, and the inducing effect of exogenous compounds on the multifunctional oxidases (MFO) and glutathione transferases (GSTs) activities of the field population was significantly reduced. Moreover, the inhibition effect of dichlorvos on sensitive population acetylcholinesterase (AChE) is significantly higher than that of field populations, and it is speculated that the broad-spectrum resistance of grassland nocturnal moth populations to insecticides may be caused by a combination of mechanisms, including microsomal multifunctional oxidase lines, enhancement of glutathione-S-transferase and esterase on the detoxification of insecticides, and decreased sensitivity to target sites (e.g., insensitive acetylcholinesterase). Similar detoxification metabolic resistance mechanisms related to organophosphorus and carbamate compounds are found in Spodoptera littoralis of the cotton moth, Nephotettix cincticeps, Plutella xylostella, Anopheles albimanus, and Locusta migratoria Pests such as manilensis have also been reported.
At present, the study of the mechanism of interaction resistance has become a hot topic in resistance research. Further studies by Zhu et al. found that the resistant populations of alkaline phosphatase (ALP), aminopeptidase (APN), glyphalase (APN), glyoxylates (1-Naspecific esterase) and naphthalene sulfonase (2-NA-specific) were found in the populations of highly resistant Cry1F transgenic maize Esterase), trypsin, and chymotrypsin activity were significantly reduced, while PNPA-specific esterase and glutathione-S-transferase activity were significantly increased, which is thought to be the metabolic resistance mechanism that causes the grassland moth to develop resistance to acetaminophos. Bolzan et al. found that fluorobenzamide and chlorhexate benzamide have a high level of cross-resistance risk, and the radiation ligand and protein binding tests have shown that although the two have different chemical structures, they can bind to insect fish nittin receptors and have common binding sites. Mutations in the insect fish nidine receptorS I4734M and G4946E have been found to be the main factors causing lepidoptera pests to develop resistance to chlorhexate benzamide. The latest study by Boaventura et al. on the mechanism of resistance to chlorpyrifosan benzamide by the grassland moth in 2019 showed that the use of different synergists to inhibit the activity of the detoxification metabolic enzyme of the grassland moth did not significantly improve the sensitivity of the resistance screening population to chlorhexate benzamide, indicating that detoxification metabolic resistance was not the main factor in the resistance of the grassland moth to chlorherode benzamide, and the sequencing of the fish nittin receptor gene showed that the mutation of the target receptor point was the main factor leading to its resistance. In addition, allele identification methods based on polymerase chain reaction (PCR) have been established to rapidly monitor the frequency of resistance genes of grassland moth to biamide insecticides such as chlorhexabenzamide.
In summary, the formation of insecticide resistance by the grassland moth is related to its enhanced activity of detoxification enzymes and reduced target sensitivity, while target receptor mutations often lead to high levels of resistance. Foreign research on the mechanism of resistance of grassland moth provides a theoretical basis for the prevention and control of drug resistance of grassland moth in China, and it is of far-reaching significance to carry out the risk assessment and mechanism of resistance risk assessment and mechanism of grassland moth to new drugs as soon as possible.
3
Discussion and outlook
The history of drug use in different regions is closely related to the resistance of pests to insecticides, and after the invasion of the grassland moth in China, due to the continuous selection of insecticides by various modes of action, it is bound to lead to the further development of its resistance to insecticides. Zhao Shengyuan et al. 2019 studies have shown that most traditional insecticides have a poor control effect on the newly invaded larvae of the grassland nightcrawler 2-year-old larvae that have recently invaded Yunnan Province, China, and relatively speaking, methylphenidate, chlorantraniliprostamide and ethyl polybactericide have very strong insecticidal activity. In 2007, Yu et al. found that the field population of the grassland nocturnal moth, which had developed resistance to carbamates and organophosphorus, did not have cross-resistance to indoxacarb, and indica had strong insecticidal activity against the field grassland night moth. Therefore, methylphenidate, chlorphenoxybenzamide and indigovirus, which do not have cross-resistance with traditional pesticides, can be considered as the preferred agents for the control of grassland moth populations to overcome the resistance of field grassland moth to traditional insecticides.
Grassland moths show different levels of resistance to pesticides in different countries, reflecting differences in pest control strategies between countries and regions. The latest research from 2019, such as Zhang Lei, shows that most of the grassland moths that invaded China's Yunnan Province are corn-type. Adamczyk et al. and Inber et al. report that different ecotypes of grassland moths have different sensitivities to agents, and corn-type resistance is higher. With the development of pest resistance to traditional insecticides, some new drugs have been promoted and applied, such as indivine is the first commercialized oxadiazine insecticide, mainly through touch killing and gastric poisoning into the insect body, has excellent insecticidal activity against lepidoptera pests, non-target biosecurity, is an alternative to organophosphorus and pyrethroid insecticide insecticides to control lepidoptera pests, chloranthramide benzamide is a new generation of biamide insecticides, its high efficiency, broad spectrum, has a good control effect on lepidoptera pests, It also controls a variety of non-Lepidoptera pests, and belvyline is a semi-synthetic, highly efficient, low-toxicity insecticide used in the control of crop pests such as vegetables, fruit trees and cotton. If a large number of such high-efficiency, low-toxicity insecticides are blindly used in the field in the short term, it is bound to increase the selection pressure of the agent on the target pest, bringing a great risk of drug resistance, so the resistance dynamics of the grassland moth in different areas should be monitored in a timely manner, and a reasonable pesticide rotation and compound drug strategy should be formulated as soon as possible to guide scientific medication to extend the service life of the insecticide in the field.
In view of the current chemical control needs faced by the outbreak of the grassland moth in China, it is necessary to learn from the existing registered agents and control experience abroad, and at the same time, combined with the research and establishment of the baseline of the sensitivity of the domestic grassland moth to the drug, reasonably carry out the field chemical control of the grassland moth, and timely carry out research on its resistance risk and resistance mechanism.
(Authors: Wang Qinqin1, Cui Li1, Wang Li1, Liang Pei2, Yuan Huizhu1*, Rui Changhui1*)
(Unit: 1. 2. Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Key Laboratory of Integrated Crop Pest Management, Ministry of Agriculture; Department of Entomology, China Agricultural University)
(Source: Journal of Pesticide Science, No. 4, 2019)