E-510 September 1940 tJHRARY SOME DETERRENTS AS A CONTROL FOR THE MELONFLY By Ralph H. Marlowe, i Division of Frii.itfly Investigations The melonfly (Dacus cucurbitae Coq.) is one of the most important insect pests of cucurbits grown in the Hawaiian Islands. The destruction of the host crops by this species has caused some growers to abandon the growing of tomatoes, y/atermeions, gourds, cucumbers, pumpkins, squashes, cantaloupes, and other cultivated hosts in many localities, as it is neces- sary to cover each fruit or vegetable with screen or paper for protection, Oviposition by the fly often causes deformities of the fruit, and the development of the larvae not only destroys the fruit, but in seme cases maggots are found living in the young plant tissues of the host. The writer has found that spraying small plots with a stomach poison does not give a good control, especially in localities where there is a high population of the melonfly. Although the fly population in an area may be reduced, the migrating females, which are usually sexually mature, may cause a high infestation of the crgp before the flies obtain a toxic dose of the poison spray. Under such conditions a repellent spray may give sufficient protection for control of tho melonfly in commercial plantings. Laboratory Results A neutral stable emulsion was prepared by dissolving coumarina in 1,4-dioxane, then mixing the coumarin-dioxane with white oil and adding this mixture to a solution containing the emulsifier, diglycol oleate. 1 The writer wishes to extend his appreciation to the Hawaii Agricultural Experiment Station for its cooperation on this project. He is indebted to J. E. Welch and the personnel at the Branch Station at Waipahu, Oahu, for the aid which they gave him by cultivating and irrigating the plots and assisting in spraying and harvesting the crop. 2 CaHeO^. Coumarin was first determined as a repellent to the melonfly in laboratory tests by Donald Starr. Monthly Report, Honolulu Laboratory, July 1936. - 2 - This emulsion gave better protection to cucumber material from oviposition by the melonfly than any of the other coumarin emulsions tested. Laboratory tests of feeding preference have shown bordeaux mixture to be repellent, as melcnflies do not like to feed on a sweet spray con- taining the fungicide. Also, a molasses spray containing nicotine sulfate was repellent. The addition of nicotine sulfate to some of the neutral diglycol emulsions caused the emulsions to break down. The emulsions remained stable when free nicotine was added. A neutral emulsion was preferable as a carrier for nicotine, since the alkaloid is more volatile in an alkaline medium. Of the nicotine-oil emulsion combinations which were tried, the emulsion formed by the addition of a mixture containing white oil and a solution of 40 percent free nicotine to the emulsifying solution gave the best protection to cucurbit material against the oviposition of the melonfly. Field Results with Deterrents The deterrents, or repellents, which were used in the field v,fork for control of the melonfly were as follows: (1) Red cuprous oxide (Cuprocide- 54) 3 pounds, nicotine sulfate solution (40% nicotine) 1 quart, v/ater 100 gallons; (2) nicotine sulfate solution (40% nicotine) 1 quart, bordeaux mix- ture (4:4:50) 100 gallons; (3) nicotine sulfate solution (40% nicotine) 1 pint, proprietary pyrethrum insecticide (Foliofume) 1 pint, water 100 gal- lons; (4) emulsion containing bentonite 4 pounds, nicotine sulfate solution (40% nicotine) 1 quart, white oil 1 gallon, water 100 gallons; (5) emulsion containing free nicotine solution (40% nicotine) 1 quart, white oil 1 gaxlon, diglycol oleate 1 quart, water 100 gallons; (6) emulsion containing coumarin 1/4 pound, dioxane 1 quart, white oil 1 gallon, diglycol oleate 1 quart, water 100 gallons; and (7) a dust made by adding 5 pounds of nicotine sulfate solution (40% nicotine) to 95 pounds of lime. The white oil used in the sprays had a Saybolt viscosity of 185-1S5. All sprays v/ere applied with a power sprayer at a pressure of 100 to 150 pounds. The deterrents were applied on a field of cucumber plants, the plots of which were laid out on the Latin square plan. The total area of the eight plots given each treatment was 3,456 square feet, or approximately C.079 acre. There were eight applications of spray between June 15 (appear- ance of bloom) and July 20, 1939. The results of the application of the deterrents are presented in table 1. Table 1. — Percentage of noninfested cucumbers and yield (in pounds) on plots to which different deterrents, or repellents, had been applied for control of the melonfly. : Percent of : Pounds of : Pounds of : cucumbers : noninfested : noninfested Deterrent :not infested : cucumbers : cucumbers :per 0.079 .-per acre acre : (calculated^ Bordeaux mixture + nicotine sulfate 76.1 611-7/8 7.712 Red cuprous oxide -f- nicotine sulfate 62.6 546-3/4 6,891 Nicotine sulfate, lime dust 61.1 : 344-3/8 4,341 Free nicotine, oil emulsion 57.4 : 329-1/2 4,153 Pyrethrum + nicotine sulfate 57.8 319-1/8 4,022 Coumarin, dioxane, oil emulsion 53.8 : 237-3/8 2,992 Bentonite, nicotine sulfate, oil emulsion 56.2 217-3/4 2,745 Check (not sprayed) 32.4 117-7/8 1.486 The infestation of the check (67.6 percent) was less than expectation, as this work follov/ed a previous experiment in v/hich tartar emetic was used. The average infestation of the tartar emetic check was 96.6 percent. The difference in infestation probably was due to the difference in the ex- perimental set-up. The unsprayed check in the tartar emetic experiment was located approximately 200 feet from the sprayed plots, while the check plots in the work on deterrents were surrounded by sprayed plots and thus received a certain amount of protection. In many small commercial plantings the infestation of the crop by the melonfly is 100 percent. Of the seven deterrents used, the bordeaux-nicotine sulfate gave the best protection against the melonfly. More clean fruits were produced by the plots sprayed with bordeaux-nicotine sulfate than by the plots sprayed with any of the other six materials. The bordeaux plots produced 1,198 clean cucumbers which weighed 611-7/8 pounds, or an approximate production of 7,712 pounds of noninfested cucumbers per acre. The treatment which rated second to the bordeaux-nicotine sulfate in protection was red cuprous cxide plus nicotine sulfate. The production was 546-3/4 pounds, or ap- proximately 6,891 pounds per acre. The deterrent which gave the next best control v/as the nicotine sulfate-lime dust. The plants which were dusted produced 344-3/8 pounds of cucumbers, or approxiraately 4,341 pounds per acre. The data were treated statistically by the method of analysis of variance. It was found that the ratio of the treatment variance to the error variance was 41.9 for the data in which the sampling unit was the percentage of noninfested cucumbers per plot and 28.01 for the data in which the sampling unit v;as the number of pounds of noninfested cucumbers per plot. Since the corresponding ratio found in the table of F (Snedecor) 3 is 3.10 for odds of 99 to 1, the ratios of this experiment may be regarded as highly significant, indicating that some real differences existed between the results of the treatments, the check, of course, included. Downy mildew appeared on a few plants in all the plots at the end of the experiment. The effect of fungus on the results of the experiment was negligible, as the infestation was light and scattered throughout the plots. The appearance of downy mildew on cucurbits toward the end of harvest is not uncommon, and the effect of the fungus on the plants is not so severe as when the plants are young and starting to bear fruit. The plants sprayed with the two copper-nicotine sulfate sprays showed no in- jury and were more vigorous and sturdy than the other plants. Effect of Aphid Infestation on the Results In Hawaii it is necessary to control aphids on curcubits in order to produce a good crop. To control the aphids all the plots were sprayed with nicotine sulfate at weekly intervals previous to the first application of the deterrents. After the second application of the deterrents the plots which had been treated with the two copper-nicotine sulfate sprays, the nicotine-oil emulsion, and the nicotine sulfate-lime dust were free from aphids except for a few winged forms. The rest of the plots were infested with aphids. All the plots were sprayed once more with nicotine sulfate. At the end of the experiment (July 20) the checks and the plots sprayed with the coumarin-oil emulsion were heavily infested with aphids. Winged forms and some nymphs were found in the plots dusted with nicotine- lime. Winged forms were found in the plots sprayed with either the nicotine- cil emulsion or the nicotine bentonite emulsion. No aphids were found in the plots sprayed with pyrethrum-nicotine sulfate, bordeaux-nicotine sulfate, or the red cuprous oxide-nicotine sulfate spray. Without a doubt the presence of aphids cut down the production in the check. Therefore the difference in production between the unsprayed 3 Snedecor, G. W. Statistical Methods. Collegiate Press, Inc., Ames, Iowa. 1938. - 5 - plants and those sprayed with the two copper sprays was not entirely due to the control of the melonfly but also to the control of the aphids. As the aphids were controlled in plots sprayed with the nicotine sulfate- pyrethrum and partly controlled in those sprayed with the nicotine-oil emulsion or dusted with the nicotine sulfate-lime, the difference in pro- duction between the plots treated with the last three mixtures and those sprayed with the copper sprays was due principally to the control of the melonfly. The plots sprayed with the bordeaux-nicotine sulfate mixture and those sprayed with the red cuprous oxide-nicotine sulfate spray produced approximately 419 percent and 364 percent more noninfested cucumbers, respectively, than the plots which were not sprayed. The revenue derived from the plots sprayed with the various insecti- cide mixtures and the approximate cost of the spray materials, respectively, are as follows: Red cuprous oxide-nicotine sulfate, $38.27, $4.49; bordeaux- nicotine sulfate, $42.83, $3.50; check, $8.25, 0; pyrethrum-nicotine sul- fate, $22.34, $3.08; bentonite-nicotine sulfate-oil emulsion, $15.24, $3.38; nicotine-oil emulsion, $23.07, $5.53; coumarin-dioxane-oil emulsion, $16,62, $6.97; and nicotine sulfate-lime dust, $24.11, $1.24. UNIVERSITY OF FLORIDA llllliiilllli 3 1262 09224 7716