- Author: Surendra K. Dara
The diamondback moth (DBM), Plutella xylostella, is a small plutellid moth of European origin that has been in North America for nearly two centuries. It is currently present in many parts of the world feeding exclusively on cruciferous hosts such as broccoli, cabbage, and cauliflower. DBM has multiple generations per year and can cause significant yield losses when populations are not controlled. Increasing temperatures that shorten pest life cycle, changing climatic patterns and milder winters in many areas, the ability of adult DBM to disperse, and the presence of cultivated and wild cruciferous crops year-round are worsening the pest problem and require continuous application of pesticides and other control options. Insecticide resistance is also a common problem in DBM where very high levels of resistance to some commonly used pesticides in field populations were reported. Although DBM infestations are common in cruciferous vegetable production, many parts of California and Arizona have seen a significant increase in DBM populations in the past few months. Year-round production of cruciferous vegetables supports DBM populations with as many as 12 generations per year and requires regular application of pesticides. Frequent pesticide applications can lead to insecticide resistance, ineffective pest suppression, and higher yield losses. A good integrated pest management (IPM) strategy is critical to address a pest like DBM.
Biology: A female moth deposits an average of 150 eggs over about 10 days (Capinera, 2018). Eggs are deposited in small batches in depressions on leaf surfaces. Small, green larvae actively feed on the foliage, first instars in mines and the remaining three on the surface. Pupation usually occurs on the lower side of the leaf surface in a loosely spun cocoon. Adult moths are slender, greyish brown with conspicuous antennae. The light-colored diamond pattern on the wings when the moth is resting gives the name diamondback moth.
Damage: Larval feeding on foliage and growing parts of young plants causes skeletonization of leaves. Larvae can also bore into the heads and flower buds resulting in the failure of head formation and stunting of plant growth. Uncontrolled populations cause significant yield losses.
A sound IPM strategy involves regular monitoring of pest infestations, a good understanding of the pest life cycle, and using multiple tactics that target one or more life stages (Dara, 2019). The following recommendations are developed based on the new IPM model and its different components.
A. Pest Management: Some pests can be effectively controlled by one or two tactics, but a difficult pest like DBM with its increasing threat needs a variety of tactics to achieve maximum control.
i) Host plant resistance: Planting cultivars that tolerate or resist DBM damage is the first line of defense. For example, cabbage cultivars with glassy leaves (Dickson et al., 1990) and a specific glucosinolate profile (Robin et al., 2017) are resistant to larval damage. On glassy leaf surfaces, larvae spend less time feeding and more time searching for a suitable spot to feed. The presence or higher levels of glucobrassicin, glucoiberin, and glucoiberverin and the absence or lower levels of 4-hydroxyglucobrassicin, glucoerucin, glucoraphanin, and progoitrin showed resistance to larval feeding in cabbage (Robin et al., 2017).
ii) Cultural control: Maintaining a brassica-free period or rotating with non-brassica crops will help break the pest cycle. Removal of weedy hosts can also reduce the source of infestation, but DBM adults can disperse in search of their hosts. Good agronomic practices can ensure optimal plant health and compensate for potential yield losses when infestations are low. Certain biostimulants can induce systemic resistance or strengthen plant tissues and further contribute to the plant health under pest attack.
iii) Biological control: Various species of natural enemies contribute to the control of DBM (Sarfraz et al., 2007). The egg parasitoid Trichogramma pretiosum and the larval parasitoids Cotesia plutellae, Diadegma insulare, Diadromus subtilicornis, and Microplitis plutellae, predatory ground beetles, hemipterans, syrphid fly larvae, and spiders are some of the natural enemies of DBM. Depending on the availability, parasitoids of other Cotesia spp. and Oomyzus spp. can also be used. Conserving these natural enemies by providing strips of insectary plants in the field along with releasing commercially available natural enemies will provide the necessary biological control of DBM.
iv) Behavioral control: Mating disruption with sex pheromone is the most effective behavioral control tactic for DBM. Using pheromones confuses the male moth in finding its female mate, reduces mating, and thus the next generation individuals. A recent study in a commercial Brussels sprouts field demonstrated the potential of mating disruption with a sprayable pheromone (Dara, 2020). Studies conducted in different countries explored the potential of various antifeedants against DBM larvae and when commercially available, such materials can contribute to DBM IPM. A triterpenoid saponin from the crucifer Barbarea vulgaris in Japan (Shinoda et al., 2002), momordicine I and II from the cucurbit Momordica charantia in China (Ling et al., 2008), and the extracts of Acalypha fruticosa (family Euphorbiaceae) in India (Lingathurai et al., 2011) are some examples of the antifeedant materials investigated against DBM.
v) Physical control: Depending on the field size, crop stage, and affordability, row covers can be used to exclude DBM.
vi) Microbial control: DBM is susceptible to naturally occurring bacterial, fungal, and viral pathogens, but biopesticides based on the bacterium Bacillus thuringiensis and the bacterial toxin spinosad are the most common microbial control options for DBM in the United States. Baculovirus-based products are available for DBM control in other countries.
vii) Chemical control: Application of chemical pesticides of natural and synthetic origin is the most commonly used tactic for DBM control. Azadirachtin, pyrethrins, and synthetic pesticides from different mode of action groups can be used against DBM. Studies conducted in Ethiopia (Begna and Damtew, 2015), India (Devi and Tayde, 2017), and Thailand (Kumrungsee et al., 2014) explored the potential of various botanical extracts against DBM with varying levels of efficacy. Vegetable oils, mineral oils, neem oil, and others can also be used as both ovicides and larvicides.
B. Knowledge and Resources: The most important aspect of IPM is to develop a good understanding of the pest life cycle, seasonal trends, host preference, feeding behavior, response to environmental conditions, and biotic and abiotic stressors. This knowledge helps to identify vulnerable stages of the pest and develop appropriate control strategies. For example, mating disruption to target adults, biocontrol agents against multiple life stages, especially eggs and larvae, oils as ovicides, and other pesticides against larvae and other life stages can tackle each stage effectively. Modern tools such as smart traps to monitor pest populations and drones for releasing natural enemies can also help improve the IPM program.
C. Planning and Organization: Since insecticide resistance is a common problem with DBM, rotating pesticides (both biological and synthetic) among different mode of action groups and avoiding repetitive application of the same or a similar pesticide are critical for resistance management. Making appropriate treatment decisions based on infestation levels and the life stage of the pest, regularly monitoring for potential resistance issues, and keeping track of combination and rotation programs that worked well are all a part of effective planning and information management that improve pest control efficacy. If necessary, aggressive area-wide management plans should be developed using one or more control options.
D. Communication: When dealing with an important pest such as DBM, effective communication will help address the knowledge gaps and contribute to effective pest management. Pest control professionals and growers can explore new DBM control options by contacting researchers, attending extension meetings, or reading various articles that can be accessed through internet, university resources, or local governmental agencies. Growers can also exchange information and develop IPM strategies that best suit their situation through a collaborative effort.
Since the field conditions, infestation levels, resistance in DBM populations, and availability and affordability of control options vary, growers should customize their IPM program to suit their local needs.
Begna, F. and T. Damtew. 2015. Evaluation of four botanical insecticides against diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae) on head cabbage in the central rift valley of Ethiopia. Sky J. Agrl. Res. 4: 97-105. http://www.skyjournals.org/sjar/pdf/2015pdf/Aug/Begna%20and%20Damtaw%20pdf.pdf
Capinera, J. L. 2018. Diamondback moth. Featured Creatures, University of Florida Publication EENY-119. https://entnemdept.ufl.edu/creatures/veg/leaf/diamondback_moth.htm
Dara, S. K. 2019. The new integrated pest management paradigm for the modern age. JIPM 10: 12, 1-9. https://doi.org/10.1093/jipm/pmz010
Dara, S. K. 2020. Mating disruption as an IPM tool in diamondback moth management. UCANR eJournal of Entomology and Biologicals. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=44160
Devi, H. D. and A. R. Tayde. 2017. Comparative efficacy of bio-agents and botanicals on the management of diamondback moth (Plutella xylostella Linn.) on cabbage under Allahabad agroclimatic conditions. Int. J. Curr. Microbiol. App. Sci. 6: 711-716. https://doi.org/10.20546/ijcmas.2017.607.088
Dickson, M. H., A. M. Shelton, S. D. Eigenbrode and M. L. Vamosy. 1990. Selection for resistance to diamondback moth (Plutella xylostella) in cabbage. HortSci. 25: 1643-1646. https://doi.org/10.21273/HORTSCI.25.12.1643
Kumrungsee, N., W. Pluempanupat, O. Koul, and V. Bullangpoti. 2014. Toxicity of essential oil compounds against diamondback moth, Plutella xylostella, and their impact on detoxification enzyme activities. J. Pest Sci. 87: 721-729. https://doi.org/10.1007/s10340-014-0602-6
Ling,B., G.-c. Wang, J. Ya, M.-x. Zhang, and G.-w. Liang. 2008. Antifeedant activity and active ingredients against Plutella xylostella from Momordica charantia leaves. Agrl. Sci. China 7: 1466-1473. https://doi.org/10.1016/S1671-2927(08)60404-6
Lingathurai, S., S. E. Vendan, M. G. Paulraj, and S. Ignacimuthu. 2011. Antifeedant and alrvicidal activities of Acalypha fruticosa Forssk. (Euphorbiaceae) against Plutella xylostella L. (Lepidoptera: Yponomeutidae) larvae. J. King Saud Univ. Sci. 23: 11-16. https://doi.org/10.1016/j.jksus.2010.05.012
Robin, A.H.K., M. R. Hossain, J.-I. Park, H. R. Kim and I.-S. Nou. 2017. Glucosinolate profiles in cabbage genotypes influence the preferential feeding of diamondback moth (Plutella xylostella). Fron. Plant Sci. 8: 1244. https://doi.org/10.3389/fpls.2017.01244
Sarfraz, M., A. B. Keddie, and L. M. Dosdall. 2007. Biological control of the diamondback moth, Plutella xylostella: a review. Biocon. Sci. Tech. 15: 763-789. https://doi.org/10.1080/09583150500136956
Shinoda, T., T. Nagao, M. Nakayama, H. Serizawa, M. Koshioka, H. Okabe, and A. Kawai. 2002. Identification of a triterpenoid saponin from a crucifer, Barbarea vulgaris, as a feeding deterrent to the diamondback moth, Plutella xylostella. J. Chem. Ecol. 28: 587-599. https://doi.org/10.1023/A:1014500330510
- Author: Surendra K. Dara
The diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) is an important pest of broccoli, Brussels sprouts, cabbage, cauliflower, collards, kale, and other cruciferous crops. It exclusively feeds on cultivated and weedy crucifers and has a worldwide distribution. Larvae feed on foliage and growing parts of young plants or bore into the heads or flower buds resulting in skeletonization of leaves, stunting of the plants, or failure of head formation in some hosts. In warmer areas, the diamondback moth has up to 12 generations per year. While multiple species of parasitoids and predatory arthropods provide some level of natural control, insecticidal applications are a primary means of diamondback moth management. Although several synthetic and biological pesticides are effective against the diamondback moth, resistance to Bacillus thuringiensis (Ferré et al. 1991), abamectin (Pu et al. 2009), emamectin benzoate, indoxacarb, and spinosad (Zhao et al. 2006), pyrethroids and other pesticides (Leibee and Savage 1992; Endersby et al. 2011) has been well-known from around the world. Excessive use of any kind of pesticide leads to resistance problems (Dara 2020; also see a video presentation) to an individual pesticide or multiple pesticides. Integrated pest management (IPM) strategy encourages the use of various control options both for maintaining pest control efficacy and reducing the risk of resistance development (Dara 2019). Regularly monitoring the pest populations to make treatment decisions, rotating pesticides with different modes of action, exploring the potential of biocontrol agents, and other non-chemical control approaches such as mating disruption with pheromones are some of the IPM strategies for controlling the diamondback moth. While sex pheromones effectively used to manage several lepidopteran pests and are proven to be a critical IPM tool, mating disruption is not fully explored for controlling the diamondback moth. A study was conducted in Brussels sprouts to evaluate the efficacy of a sprayable pheromone against the diamondback moth and to enhance the current IPM strategies.
The study was conducted on a 10-acre Brussels sprouts field in Santa Maria. Cultivar Marte was planted in early July 2020 with expected harvesting in mid to late December. A typical diamondback control program includes monitoring diamondback moth populations with the help of sticky traps and lures and applying various combinations of biological and synthetic pesticides at regular intervals. This study evaluated the efficacy of adding CheckMate DBM-F to the grower standard practice of monitoring the diamondback moth populations with traps and lures and applying pesticides. Treatments included i) grower standard pesticide program (Table 1) and ii) grower standard pesticide program with two applications of 3.1 fl oz of CheckMate DBM-F on 9 August and 11 September. Treatment materials were applied by a tractor-mounted sprayer using a 100 gpa spray volume and necessary buffering agents and surfactants. Each treatment was 5 ac and divided into four quadrants representing four replications. In the middle of each quadrant, one Suterra Wing Trap was set up with a Trécé Pherocon Diamondback Moth Lure. Lures were replaced once a month in early September and early October. Sticky liners of the traps were replaced every week to count the number of moths trapped. Traps were placed on 1, 12, and 24 August, 1, 11, 18, and 27 September, and 6 October and the moth counts were taken from respective traps on 8 and 20 August, 1, 11, 18, and 27 September, 6 and 15 October. CheckMate DBM-F was applied at 3.1 fl oz/ac on 9 August and 11 September. The number of larvae and their feeding damage on a scale of 0 to 4 (where 0=no damage, 1=light damage, 2=moderate damage, 3=high damage, 4=extensive/irrecoverable) were recorded from 25 random plants within each replication on 30 August and 6 and 18 October. Data were subjected to analysis of variance using Statistix software and significant means were separated using Tukey's HSD test. The retail value of various pesticides was also obtained to compare the cost of treatments.
Table 1. Pesticides, buffering agents, and surfactants, their active ingredients, rates/ac (along with the IRAC mode of action groups), and retail pricing for those applied in the grower standard diamondback moth control program.
When CheckMate DBM-F [(Z)-11-Hexadecenal (3) , (Z) - 11 - Hexadecen-1-yl Acetate (1)] was applied the first time on 9 August, Dibrom 8 Emulsive was replaced with Warrior II, the buffering agent Quest was not used, and the surfactant Dyne-Amic was replaced with Induce (dimethylpolysiloxane) to avoid potential compatibility issues. The impact of this substitution is expected to be negligible within the scope of this study. The retail cost of 3.1 fl oz CheckMate DBM-F is $45.60. The cost of lures and traps would be about $4-8 per acre for a six-month crop like Brussels sprouts.
Results and Discussion
Moth populations: Traps in replication 4 in both treatments on 8 August and replication 1 in the grower standard were missing, probably knocked down by a tractor. The day before CheckMate DBM-F was first applied, the mean number of adult diamondback moths caught were 227 in the grower standard and 271 in the plots that would receive the pheromone application. There was a gradual decline in moth counts during the rest of the observation period in both treatments. However, the decline was higher in the plots that received CheckMate DBM-F. The number of moths per trap were about 19% higher in the pheromone-treated plots compared to the grower standard before the study but were nearly 98% lower by the end of the study. The reduction in moth populations from mating disruption was significant on 18 September (P =0.039) and 15 October (P = 0.006).
Larval populations: The mean number of larvae per 25 plants in a replication was zero on all observation dates except for 0.01 on 30 August in the plots that received CheckMate. Four insecticide applications by the time the study was initiated, and the remaining six applications effectively suppressed larval populations.
Damage ratings: Larval feeding damage ratings were consistently low (P < 0.0001) in the plants that did not receive CheckMate DBM-F. The damage was limited to the older leaves at the bottom of the plants and must have been from early feeding before the initiation of the study. The lack of larvae and the evidence of new feeding damage also confirm that the crop remained healthy and pest-free.
Since frequent pesticide applications effectively suppressed larval populations and prevented their feeding damage, the effectiveness of mating disruption in reducing yield losses could not be determined in this study. Since larval counts were not made weekly or between pesticide applications, those that were probably present between the pesticide applications could not be determined. Moths found in the traps probably developed from the larvae in the field or could have been those that flew in from other areas. However, lower moth populations in CheckMate DBM-F treatment demonstrated the overall influence of mating disruption and pest suppression.
It is common to make about 10-12 pesticide sprays during the 6-month crop cycle of Brussels sprouts. The cost of each application varied from about $73 to $192 depending on the materials used with an average cost of about $128 per application in this study. The cost of two CheckMate DBM-F applications is $91. If diamondback moth populations could be reduced with mating disruption, it is estimated that 2-3 pesticide applications could be eliminated. That results in $164 to $292 of saving for the pesticide costs and additional savings in the application costs per acre by investing $91 in the mating disruption. Since the diamondback moth can develop resistance to several chemical and natural pesticides, eliminating some applications as a result of mating disruption also contributes to resistance management along with potential negative impact of pesticides on the environment. Compared to other mating disruption strategies, a sprayable formulation compatible with other agricultural inputs is easier and cost-effective to use.
This study demonstrated that mating disruption with CheckMate DBM-F will significantly enhance the current IPM practices by reducing pest populations, contributing to insecticide resistance management, and reducing pest management costs. Additional studies, with fewer pesticide applications that allow larvae to survive and cause some damage, might further help understand the role of mating disruption where pest populations are not managed as effectively as in this field.
Acknowledgments: Thanks to the PCA and the grower for their research collaboration, Tamas Zold for his technical assistance in data collection, Ingrid Schumann for market research of pesticide pricing, and Suterra for the financial support.
Dara, S. K. 2019. The new integrated pest management paradigm for the modern age. J. Int. Pest Manag. 10: 12.
Dara, S. K. 2020. Arthropod resistance to biopesticides. Organic Farmer 3 (4): 16-19.
Endersby, N. M., K. Viduka, S. W. Baxter, J. Saw, D. G. Heckel, and S. W. McKechnie. 2011. Widespread pyrethroid resistance in Australian diamondback moth, Plutella xylostella (L.), is related to multiple mutations in the para sodium channel gene. Bull. Entomol. Res. 101: 393.
Ferré, J., M. D., Real, J. Van Rie, S. Jansens, and M. Peferoen. 1991. Resistance to the Bacillus thuringiensis bioinsecticide in a field population of Plutella xylostella is due to a change in a midgut membrane receptor. Proc. Nat. Acad. Sci. 88: 5119-5123.
Leibee, G. L. and K. E. Savage. 1992. Evaluation of selected insecticides for control of diamondback moth and cabbage looper in cabbage in Central Florida with observations on insecticide resistance in the diamondback moth. Fla. Entomol. 75: 585-591.
Pu, X., Y. Yang, S. Wu, and Y. Wu. 2009. Characterisation of abamectin resistance in a field-evolved multiresistant population of Plutella xylostella. Pest Manag. Sci. 66: 371-378.
Zhao, J-Z., H. L. Collins, Y-X. Li, R.F.L. Mau, G. D. Thompson, M. Hertlein, J. T. Andaloro, R. Boykin, and A. M. Shelton. 2006. Monitoring of diamondback moth (Lepidoptera: Plutellidae) resistance to spinosad, indoxacarb, and emamectin benzoate. J. Econ. Entomol. 99: 176-181.