Y BOARD July 1949 E-783 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine INSECT- PROOFING COTTON BAGS By Richard T. Cotton and Justus C. Frankenfeld, Division of Cereal and Forage Insect Investigations, Bureau of Entomology and Plant Quar- antine, and Winston B. Strickland, Southern Regional Research Lab- oratory, Bureau of Agricultural and Industrial Chemistry. Insect infestation of milled cereal products after they have been bagged or packaged is a matter of great concern to manufacturers, marketers, and consumers of such products. Insects readily enter paper bags and fiber-board packages through small openings at the point of closure, through needle holes in sewn bags, or by boring directly through the paper or fiber board. The resistance of fabric bags to insect entry depends on the kind of fabric. The coarser the weave the more easily the fabric is penetrated. Adult insects may thrust their ovipositors through the fabric and deposit their eggs in the food material within, or the small larvae may crawl through needle holes along the seams and at the top of the bags, or directly through the meshs of the fabric. Search for a Suitable Repellent It was thought that the method of insect-proofing bags offering most promise was impregnation of the material with a chemical repellent. In 1940 tests were made with a number of repellents at the Manhattan, Kans., laboratory of the Bureau of Entomology and Plant Quarantine. Paper impregnated with a 1-500 nicotine solution or a 2-percent solu- tion of sodium silicofluoride showed excellent resistance to penetration. Both paper and cotton bags impregnated with various concentrations of nicotine sulfate were tested, with varied effectiveness. In experiments since 1940 many chemicals have been applied to paper and fabric bags by dipping or by incorporation in sizing or coating materials. Toxic materials such as DDT were found to give excellent protection, but were not considered suitable for use with fabric bags because it was difficult to combine them with the fabric in such a manner that they would not contaminate the packed product. A repellent that was nontoxic to warm-blooded animals appeared to be necessary. In 1943 paper impregnated with pyrethrum extract was found to be an excellent insect repellent. - 2- In June 1946 various mixtures of pyrethrins with piperonyl butoxide or piperonyl cyclohexanone were obtained for testing. Two formula- tions- -0.5 percent of pyrethrins plus 5 percent of piperonyl butoxide and 0.25 percent of pyrethrins plus 5 percent of piperonyl cyclohexanone- - both in deodorized kerosene with an emulsifier added, were used to impregnate both paper and cotton bags. These formulations were used both at full strength and in dilutions in water at 1 to 9 and 1 to 14 parts by volume. Both kinds of bags treated with these mixtures at full strength gave excellent resistance to pentration for a long time. Impregnated cotton Dags filled with insect-free flour were exposed to heavy infestation from July 1946 to July 1947. On examination the bag treated with the pyrethrins -piperonyl butoxide formulation contained 2 dead flat grain beetles ( Laemophlocus minutus (Oliv.)) and the bag treated with the pyrethrins -piperonyl cyclohexanone formulation con- tained 1 dead confused flour beetle ( Trifolium confusum Duv.). An un- treated bag contained 182 live flour beetles and 26 live flat grain beetles. Baking tests conducted by the Milling Department of Kansas State College in July 1946 showed no ill effect of the chemicals on the baking qualities of flour packed and stored in the treated bags. Development of Methods of Impregnating Bags Tests with cotton bags were continued to determine minimum ef- fective dosages and to perfect commercially practicable methods of application. The material for the bags was prepared at the Southern Regional Research Laboratory of the Bureau of Agricultural and Indus- trial Chemistry, at New Orleans, La. Unbleached sheeting having 48 yarns per inch in both warp and filling was impregnated with water dispersions of a 1-10 pyrethrins -piperonyl butoxide mixture in connection with the usual padding process, of such strengths that the finished cloth contained 5, 2.5, or 1.25 mg. of pyrethrins per square foot. To insure complete and uniform penetration, a wetting agent of the sulfated fatty- alcohol type was used, and the padding mixture was heated to boiling. The treated cloth was then dried in a hot-air drier at 212° F. Bags 5 by 8 inches made from the treated cloths were filled with insect-free flour and exposed to insect infestation for 8 months. Good protection was obtained with bags treated at the highest dosage but not at the two lower dosages. In another series of tests bags made from unbleached cotton cloth treated with different dosages of 1-10 mixture of pyrethrins and pip- eronyl butoxide and also with pyrethrins alone were filled with insect- free flour and exposed for 7 months to continuous infestation by the -3- confused flour beetle, the cadelle ( Tenebroides mauritanicus (L.)), and the Mediterranean flour moth (ffphestia kuehniella Zell.). At the end of the second, fourth, and seventh months the bags were examined and the number of insects recorded, and the bags refilled with insect-free flour. The data given in table 1 indicate that satisfactory protection against these insects for a 7-month period was afforded by pyrethrins used alone or in combination with piperonyl butoxide, at all the dosages tested. Table 1.- -Resistance of cotton bags treated with various dosages of pyrethrins, with and without piperonyl butoxide, to penetration by insects. Dosage of repellent (milligrams per square foot of cloth) Number of bags treated Average number of insects per bag after- - Pyrethrins Piperonyl butoxide 2 months 4 months 7 months 10 7. 5 10 20 50 Untreated 00 4 1.75 75 4 1 1. 25 50 4 . 25 2 3 1 3 1 3 0.33 1 60 60 443 The pyrethrins deteriorate rapidly when exposed to light. To de- termine whether the repellency of treated cotton bags would also be affected by exposure to light, bags made of cloth treated with the 1-10 pyrethrins -piperonyl butoxide formulation at the rate of 10 mg. of pyrethrins per square foot were filled with insect-free flour and exposed to insect infestation in darkness, in indirect light, and in direct sunlight. When the flour was examined at the end of 7 months, it was found that the insect repellency was retained under all con- ditions. In the investigation of techniques for applying the repellent to cotton cloth, the 1-10 pyrethrins -piperonyl butoxide formulation was applied to warp yarn during the sizing operation. The sizing con- sisted of 15 ounces of 40-fluidity thin boiling cornstarch per gallon of water, cooked by boiling with an open steam line for 1 hour, to which 6 percent of emulsified beef tallow, based on the weight of the starch, was then added. The insect repellent was also added after the starch was cooked. The cooking of the starch and the sizing operation were UNIVERSITY OF FLORIDA -4- 3 1262 09239 2363 carried out in the laboratory under conditions similar to those in mill practice. The sized warp was wound on a loom beam and woven into sheeting 12 3/4 inches wide, with untreated filling. The cloth weighed approximately 5 1/2 ounces per square yard, and contained 46 by 50 yarns per square inch. The dosages of the pyrethrins-piperonyl butoxide mixture were such as to give 8 and 4 mg. of pyrethrins per square foot. Identical cloth was woven for bags from yarns containing no repellent. It should be emphasized that in the treated cloth only the warp yarns contained the repellent. If both warp and filling had been treated, the dosages would have been about twice as heavy. The cloth was made into bags which were filled with insect-free flour and tested over a 4- month period. At the end of this time no insects were found in four replicate bags treated at the higher dosage, and only 1 insect in one of the four bags treated at the lower dosage. To test the persistence of the treatment on unfilled bags, treated bags were stored for 5 months and then filled with flour and exposed for 2 months to an extremely heavy infestation of Mediterranean flour moths, confused flour beetles, cadelles, and lesser grain borers ( Rhyzopertha dominie a (F.)). No insects penetrated any of the bags that had been treated at either dosage, whereas untreated bags exposed to the same infestation contained so many insects that it was impractical to count them. During the test period insects were seldom seen on the treated bags, whereas large numbers crawled over the untreated bags. There was little mortality of flour beetles forced to remain on treated cloth for long periods. Conclusion These experiments show that bags made from cotton that has been treated with the extremely light dosages of pyrethrins, alone or mixed with piperonyl butoxide, as discussed above, will protect flour packed therein from insect infestation for at least 7 months. These chemicals are of a comparatively low order of toxicity to warm-blooded animals, and it seems unlikely that at the rates and methods of application used in these experiments they will contaminate products packed in treated bags. Further work is needed, however, to settle this question and to determine the minimum effective dosages. Treated cloth is not materially changed in appearance. Pyrethrins give it a slight though not objectionable odor. At present prices the cost of the treatment is low enough to make commercial application practicable. Manufacturers of fabrics for cotton bags may find it possible to treat warp yarns during sizing at no additional cost other than that of the chemicals.