Non-Woven Obstructive Barriers for Control of Insect Pests - Final Report

Disclaimer

This report was prepared by an EPA assistance agreement recipient and represents only the views of the author rather than EPA.

Project Coordinator

Michael P. Hoffmann
Joel M. Baird
Department of Entomology
Cornell University
Insectary Building
Ithaca, NY 14853, USA

Abstract

Alternatives to conventional insecticides are needed. Many arthropod pests have become resistant to insecticides, environmental and health hazards have been documented and non-target organisms have been adversely affected. In addition, the potential loss of many insecticides due to enactment of the Food Quality and Pesticide Act will further decrease the insecticide options available to protect crops from insect pests. We investigated non-woven fiber barriers, a novel mechanical control that holds considerable potential as an alternative to conventional insecticides. Non-woven barriers consist of arrangements of minute fibers in "web" form or loosely intertwined like very porous "cotton candy". Results from a series of experiments demonstrated that non-woven fiber barriers significantly reduce egg laying by major agricultural insect pests on several different crops. The pests we tested included the imported cabbageworm (pest of cruciferous crops), whitefly (wide ranging greenhouse and field crops pest), corn earworm (pest of corn, tomatoes and cotton) and cabbage and onion maggot (pests of cruciferous crops and onions, respectively). Results showed that the effectiveness of fiber barriers varied depending on the type and density of fiber barrier and how it was configured on the plant. At least with the colors we tested, fiber color did not consistently have a significant affect on control of the insect pests. We also tested delivery systems for fiber barriers including electrostatic spinning and melt extrusion. Both of these technologies are widely used in the textile industry and elsewhere. We found them to be very adaptable to our needs for generation of non-woven fiber barriers. Fiber barriers generated with both of these systems were effective in reducing or preventing egg laying by insect pests. In its present state, electrostatic spinning is most applicable in controlled environments, such as greenhouses, whereas melt extrusion is more portable and functions well under field conditions. Further modifications of these technologies will no doubt expand their range of application. Results with insects that feed directly on plants were less encouraging. The non-woven fiber barriers tested against Colorado potato beetles, flea beetles and cucumber beetles were only partially effective. Further optimization of barriers may yet show that non-woven barriers can also control these types of insects.

This research has greatly advanced the concept of non-woven barriers for insect control. It has also resulted in spin off research into the value of non-woven barriers for avian and vertebrate pest management. In their final form, we expect non-woven fiber barriers to be a cost-effective and environmentally safe alternative to insecticides. Barriers would successfully suppress insect infestations, degrade at a specific time to non-polluting compounds and not interfere with plant growth or pollination. We tested non-woven fiber barriers against several key insect pests and obtained very encouraging results. This technology has a wide range of potential uses against other insect pests in other agricultural systems.

Background/Justification

Alternatives to conventional insecticides for control of insect pests are required. Over 500 arthropod pests have become resistant to insecticides, environmental and health hazards have been documented and non-target organisms have been adversely affected. Alternatives to conventional insecticides, and tactics promoted by the integrated pest management (IPM) strategy, include biological, cultural, physical and mechanical controls. Mechanical controls, or specifically mechanical barriers, the subject of this project, reduce insect populations by affecting them directly or radically altering their physical environment (Pfadt 1978). Barriers that prevent insect pests from reaching the crop are not new, but most investigated to date have been of a solid design (i.e., sheets of woven material, plastic mulches, etc.) (Chalfant et al. 1977, Schalk et al. 1979, Wells and Loy 1985, Perring et al. 1989, and Conway et al. 1989). Although often effective, current barriers are cost-prohibitive, labor intensive, difficult to dispose of and/or pose problems for plant development and pollination. This project investigated novel non-woven barriers consisting of arrangements of minute fibers that a-re intended to prevent egg laying or damage by insects without the disadvantages of existing barrier technologies as noted above. Important advantages of non-woven fiber barriers is that they can be made from biodegradable compounds with adjustable longevity and can be applied using existing technology such as electrostatic extrusion and/or melt extrusion.

Prior to submission of this proposal we had conducted preliminary tests with various commercial fibers and demonstrated that at least for some insects, fiber barriers held considerable potential. Building on these earlier encouraging results we focused on three general types of pest/vegetable crop situations which should be amenable to control by fiber barriers: 1) moths and butterflies which lay their eggs directly on the plant surfaces, 2) maggot adults (flies) which lay their eggs in soil at the base of the plants, and 3) beetles which feed directly on the newly emerged foliage. Examples of each type follow.

The corn earworm is a good example of a moth whose egg-laying behavior on plant tissue can potentially be modified through the use of fiber barriers. Because the females deposit up to 85% of their eggs directly on the silks of corn, it is very difficult to control the larval stage, which quickly bore through the silks and into the ear where they are protected from most insecticides. Frequent applications of insecticides (i.e., at 2-3 day intervals) are required to kill larvae during the 2 to 3 week period when ears are susceptible to damage (e.g., 12-14 insecticide applications on Long Island, NY and up to 20 in Florida (Mitchell 1978)). Because of the high use of insecticides in sweet corn and the resulting economic and environmental costs, fiber barriers may be an economically viable alternative to frequent application of insecticides.

Pests which lay their eggs at the base of the plant and whose larvae feed on the roots of seedlings are particularly troublesome to growers and usually require prophylactic treatment with synthetic insecticides. 'Me main pest complex, which attacks vegetable roots, are the various species of maggots. An example is the cabbage maggot which feeds on a host of cruciferous crops (broccoli, cabbage, cauliflower) and whose damage may result in death of the plant, diminished yields, or unmarketable roots (e.g. turnips). Because of the similar size and behavior of these maggot pests, it is likely that one type of fiber barrier would be suitable for a host of crop/pest situations and may constitute a large market.

Cucumber beetles are the most important direct feeding pests of cucurbits (cucumber, squash, pumpkin, etc.). They are especially difficult for organic growers to control because of limited control options. Our goal was to develop fiber barriers that would disrupt the beetle's ability to find or feed on the plants.

Objectives (as listed in proposal):

Overall: To reduce insecticide inputs by using environmentally benign biodegradable fiber barriers to protect crops from insect pests.

Optimize fiber types and configurations (e.g., density per unit area, distance from plant tissue, color, reflectivity) of obstructive barriers.
Optimize the delivery system(s) for fiber applications to crops.
Test both the fiber barrier and delivery system under field conditions for its efficacy in preventing pest injury, its biodegradability (field-life), and the ease and efficiency with which the barrier can be applied.
Test fiber barriers and delivery systems for efficacy against additional pest/crop combinations to determine the breadth of possible uses and benefits.

Methods and Materials

Experimental Insects

Non woven fiber barriers were tested for efficacy against insects that lay their eggs on or near crop plants, these included imported cabbageworm, com earworm, silverleaf whitefly, cabbage maggot, onion maggot and fungus gnats. Prevention of egg laying would result in a reduction in damage from the immature stages of the pest. We also evaluated fiber barriers against insects that feed directly (damage) on crop plants. These included cucumber beetles, Colorado potato beetles and flea beetles.

Commercially Available Fiber Treatments

As a first step to determine the feasibility of non-woven fiber barriers, several commercially available fiber types were evaluated. These fibers would not necessarily be practical in field applications, but were used in initial tests to determine if the non-woven fiber barrier concept had potential. Commercial fibers included 900 denier polyester (Allied Signal Corporation, Petersburg, VA), graphite (Hercules Fibers, Washington, DE), 840 denier polyester in white, red, blue, burgundy, green and yellow, (Allied Signal Corporation, Petersburg, VA), 1280 denier, black Unitaka polyester fiber (Unitaka), fiberglass, G fiber, 750 yds./lb., (Owens-Coming Fiberglass Corp., Waxahachie, TX), cosmetic cotton balls (Topco Associates, Inc., Skokie, ]IL) and elastic acrylic web (Rubie's Costume Co, Inc., Richmond Hill, NJ).

AR commercially available fibers used in trials were applied by carefully teasing apart a tow of a specified length. A "tow" consists of multiple continuous fiber filaments. A 5 cm length of tow was our standard measure of fiber for trials. For example, a density of 3, consists of three 5 cm lengths of tow. Densities tested included 3, 6, 9, and 12. Commercially available fibers were applied in a two dimensional, interlaced layer at the base of the host plant (broccoli or onion seedling). The radius of the barriers around the plant stem was approximately 7.5 cm.

In Situ (sprayed on) Fibers

Because trials with commercially available fibers showed potential, we proceeded to evaluate non-woven barriers generated in situ. We selected two types of in situ fiber production methods, electrostatic spinning and melt extrusion, both of which are widely used in the textile industry (Walczak 1977). The elecrostatically spun fibers were made from polyvinyl alcohol (PVA) (ICN Pharmaceuticals, Inc., Costa Mesa, CA) and melt extrusion fibers from ethylene vinyl acetate (EVA) (Elvax 200W or 205W, Dupont Polymers, Wilmington, DE).

For initial trials we fabricated small-scale prototype apparatus to generate fibers by either method. Electrostatically spun fibers were generated by charging (+ positive) an -8% PVA water solution (contained in a I ml glass syringe) and drawing it to a plant (- negative) through a small orifice (needle on syringe). The differential charge between the solution (+) and the plant (-) provided the force to draw small fibers from the orifice to the plant. This apparatus generated non-uniform fibers 0.05 to 2.0 pm in diameter. The distance between the needle and the plant was approximately 7 cm. To obtain complete coverage, the plant (e.g., broccoli seedling) was rotated during the application process. Approximately, 1 gm of PVA fibers were applied per seedling. The resulting barrier was fine, light-reflective and translucent, much like a cobweb, and enveloped the entire seedling.

To generate fibers by the melt extrusion process, hydraulic pressure was used to extrude molten EVA through a small orifice. Resulting fibers were carried to the target by a stream of air. The prototype melt extrusion apparatus consisted of a metal reservoir (16 cm H, 10 cm dia.) that was heated to -150-180 C and pressurized to -172.4 kPa with C02 gas.

The pressure forced the molten EVA through a 2 mm ID nozzle orifice located near the base of the reservoir. Fibers from this prototype unit ranged from -20-250 pm in diameter.

The fibers generated by both prototype electrostatic and extrusion apparatus were found to be effective. Consequently, we obtained commercially-available equipment to generate melt extrusion fibers for more extensive and larger scale field trials. The unit consisted of a Dynamini™ adhesive supply unit, 3.7 m Dynaflex™ hose (ITW Dynatec, Hendersonville, TN) and Dynagun™ hot melt applicator MODEL 155 with a 0.787 mm nozzle orifice (GracoLTI, Monterey, CA). The unit and 5.5 hp compressor was powered in the field by a 5000 watt generator. All of which was mounted on a flat bed trailer. The unit was designed to apply hot melt glue (ethylene vinyl acetate) in industrial settings, however we selected it for our trials because it allowed us to easily generate a range of fiber characteristics by varying temperature, pressure and nozzle configuration. It also permitted us to produce fibers made from various compounds and of various colors. Blue, yellow, red and black fibers were created through the addition of Colormatch plasticizer pigments (Plasticolors, Inc., Ashtabula, OH) at a rate of 4g plasticizer/450g EVA.

When used in trials, fibers produced by the Dynamini™ unit were applied directly to the soil around the plant's base (maggot trials) or applied directly onto plants for control of moth and butterfly pests. Rates of application varied depending on the pest being controlled. The fibers generated were 5-50 pm in diameter. A third, but minor method of fiber creation involved the use of a "cotton candy" machine to generate sucrose fibers.

Experimental Protocols - Greenhouse Trials

Both choice and no-choice trials were conducted. No choice (one treatment per arena) arenas consisted of 21 soda bottles modified to permit placement of soil and a plant in the bottom and to allow introduction of test insects. Choice trials were conducted in 30.48 x 30.48 x 30.48 or 45.7 x 45.7 x 45.7 cm wire mesh containers containing multiple plants each with a different treatment. Some trials were conducted in a small greenhouse containing treated plants. Insects were released directly into the greenhouse. Control plants received no treatment while experimental plants received a treatment of a specified number and length of commercially available fiber tow or, in the case of in situ fibers, applied for consistent time periods per plant or until full coverage was attained. Under no choice conditions, a single insect was placed in the arena, whereas in choice trials several insects were released into the arena.

The effect of fiber barriers on egg laying was assessed by recording the number of eggs laid on the plants, on fibers or in the soil (maggot pests). Trials typically were conducted for 24 to 72 hrs, depending on the rate of oviposition or damage to plants. Damage to plants was compared among fiber treatments by quantifying the leaf area damaged by the pest insect.

Experimental Protocols - Field Trials

Trials were performed at the Homer C. Thompson Vegetable Research Farm (Cornell University, Department of Entomology) Freeville, NY. Depending on the insect being tested, trials were either conducted in PVC framed 60.9 x 91.4 x 60.9 cm cages covered with fine netting or in large walk-in cages (approximately 3.0 x 3.8 x 2.3 m). Plants (broccoli) were transplanted into cages or cages were placed over field grown plants (sweet corn). Plants treated with fiber barriers were arranged within cages randomly, generally with each plant or groups of plants being considered replicates. As with greenhouse trials, plants Were searched and eggs recorded by location (e.g., top, bottom of leaf) on plant. Additional trials were conducted with plants exposed to natural infestations of pests.

Experimental Design and Statistical Analysis

AR the experiments were arranged in either a completely randomized or a complete randomized block design and data analyzed using SuperAnova™ (Abacus Concepts, Inc. 1989) or SigmaStat (Jandel Scientific 1993). Within no choice and choice experiments, treatments were replicated 3-10 times. In experiments repeated on different days with different plants and insects (e.g., corn earworm), data were pooled across dates. Data were square root transformed and proportions arcsin square root transformed prior to analyses as needed. Actual means are presented with their standard errors. Mean separation was performed with Fisher's LSD (p = 0.05). AR references to "significantly different" reflect a P value of <0.05.

Results and Discussion

Imported Cabbageworm

In all but one trial, fiber barriers significantly (P < 0.05) reduced egg laying by the imported cabbageworm on broccoli seedlings/plants (Table 1). In the earliest trials under no choice greenhouse conditions, and using commercial fibers placed on broccoli plants, EVA, graphite, polyethylene all significantly reduced egg laying (Table 1a). EVA was the most effective of the materials tested. In subsequent trials, under field or greenhouse conditions, sprayed on EVA significantly reduced egg laying in two of the three trials (Table 1b, c, d). Although the various densities of EVA applied (based on duration of application with the Dynamini unit) were not significantly different, there were definite trends (Table 1e, f, g). For example, a 3-fold increase in EVA fiber applied (15 vs 5 s) resulted in a >20 fold reduction in the number of eggs laid per plant (Table 1e). Lastly, fiber color did not have a significant effect on egg laying by imported cabbageworm. No differences were recorded among broccoli plants treated with sprayed on red, black or clear EVA (Table 1h). AR colors and the clear were however, significantly different from the control.

Corn Earworm

Results with corn earworm were also encouraging and showed that fiber barriers reduced the proportion of eggs laid on silks of ears of sweet corn (Table 2). Female corn earworm lay most of their eggs directly on the silks so reductions in egg laying in this area could result in reduced damage. In the first test where EVA was applied to the ear zone, 7% of all eggs on the plant were laid on silks vs 22% with no treatment (Table 2a). In the second trial, fibers reduced the proportion of eggs on silks from 36.3 (control) to 15.2 % (EVA) (Table 2b). In the third trial, both a broadcast (draped over corn plants) and directed (ear zone) application of EVA significantly reduced the percentage of eggs laid on silks (Table 2c). Although it varied among experiments, the results suggest that application of EVA may also cause a general reduction in the number of eggs laid on the entire plant. This was most apparent in second trial and with the broadcast application in the third trial.

The imported cabbageworm is a major pest of cruciferous crops in the US and elsewhere. The corn earworm, also known as the tomato fruitworm and cotton bollworm is a major insect pest of sweet corn, tomatoes and cotton. Results of these studies with nonwoven fiber barriers were very encouraging and indicate that such fiber barriers hold considerable potential. Additional trials need to be conducted to further optimize fiber types, colors and configurations on crop plants. These studies have taken us well beyond the feasibility stage. We have shown efficacy and that technologies exists to deliver fibers.

Silverleaf Whitefly

Silverleaf whitefly, is a pest of many crops, especially those gown in greenhouses, was also suppressed by fiber barriers. In an initial trial, all commercial fibers tested reduced egg laying by female whiteflies on squash plants (Table 3a). Of the three fibers tested, cotton fibers were the most effective. In another trial, the number of eggs laid by female whitefly on squash cotyledons decreased with increasing density of graphite fibers (Table 3b). In general, elecrostatically applied PVA significantly reduced egg laying on squash plants (Table 3c, d). Although the number of eggs laid directly on plant surfaces was greatly reduced a large number of eggs were laid on the fibers themselves (non-leaf). Eggs laid directly on fibers and larvae emerging from these eggs would be exposed to additional environmental stress and incur higher mortality than if laid directly on plant surfaces. Additional research is required to determine to quantify the extent to which damage from whitefly is reduced by fiber barriers.

Given that whiteflies are ubiquitous pests, especially in high value greenhouse systems where vegetables and flowers are produced, non-woven fiber barriers should be cost effective. We also conducted preliminary trials with fungus gnats, another pest of greenhouses that reproduce in potting soil. Fiber barriers sprayed over the soil resulted in a barrier that greatly reduced egg laying by female flies. Again, in the high value greenhouse system non-woven fiber barriers may hold potential for control of this pest as well.

Cabbage and Onion Maggots

Initial tests with various commercial fibers provided evidence that non-woven fiber barriers would reduce egg laying at the base of cruciferous plants by the cabbage maggot. All applications of different types of commercial fibers reduced egg laying (Table 4a). Likewise, tests of various commercial fibers against the onion maggot showed significant reductions in egg laying. Acrylic web and polyethylene proved to be the most effective at reducing egg laying near the base of onion seedlings (Table 4b). Increasing density of graphite fibers did not result in a corresponding decreasing number of eggs laid by female flies (Table 4c). Fiber color, whether applied by hand or sprayed on (EVA) did not have a significant effect (Table 4d, f, g). However, in all tests, sprayed on EVA significantly reduced the number of eggs laid (Table 4e, f, g).

The cabbage maggot is a major insect pest of cruciferous crop whereas the onion maggot is a serious pest of Allium crops. The results reported herein for management of these two pests with non-woven fiber barriers are very encouraging. ne recently enacted Food Quality and Protection Act is likely to seriously affect the availability of insecticides widely used to control maggot pests. In particular, soil applied insecticides such as chlorpyrifos (Lorsban) are at risk. Non-woven fiber barriers could provide an excellent alternative if this and other compounds are lost. There is also an ongoing threat of insecticide resistance, especially in onion maggot where in New York for example, all onion fields are treated with the same at-planting insecticide each year. Availability of an effective alternative such as non-woven fiber barriers would eliminate this potential problem. We do not envision, insects developing "resistance" to barriers.

Cucumber beetles, Colorado Potato Beetle and Flea Beetles

Initial tests were conducted with these insect pests but results were not as encouraging as with the insects discussed above (data not presented). The larger beetle pests (cucumber and potato beetle) were typically able to break through the non-woven fiber barriers and access the plant. Flea beetles were able to penetrate most of the fibers tested and feed on the test plants. Non-woven fiber barriers may be effective for these types of pests, but additional research is needed to optimize fiber type and configuration on plants.

Summary

We have shown that non-woven fiber barriers hold considerable potential for management of insect pests. We have also shown that technologies to deliver fibers to target crop plants in the field are available. Initially, obstructive fiber barriers and their application may be more expensive than insecticide applications. However, as technology improves and the market becomes wider, their cost will decrease and they should become more economically competitive. We have initially focused on controlling insects infesting high value crops (vegetables, greenhouse), but if economical, this technology also has the potential for use on many other crops. Potential modifications could create more applications including the addition of an adhesive agent to the fibers (i.e., spider web-like) and using larger fibers to simulate oviposition substrates (i.e., corn silk). In fact, at the present and in cooperation with wildlife managers, we are evaluating the use of capsaicin (hot pepper) impregnated EVA fibers for control of deer on urban ornamentals. We are very optimistic that this technology will contribute to improved pest management and reduction in need for conventional insecticides. All of which will be beneficial to the environment.

Literature Cited

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