IMlMlStalM 0(^MHllMntOf A#lcultur« Ecological Impact Agicultural R^earch Service Of Parathlon Technical BulMin NufTitoer1Ô6& In Soybeans A4 ^'/'^ cO ■-0 Vegetative Fauna (Part I) Abstract Marston, N. L, and Hennessey, M. K. 1982. Ecological Impact of Parathion in Soybeans.—Vegetative Fauna. U.S. Department of Agriculture, Technical Bulletin 1665.28 p. An application of ethyl parathion to flowering soybeans reduced populations of predatory arthropods by 66 percent 6 days posttreatment. Egg and lan/al parasites of the green cloverworm, Plathypena scabra (F.), the most abundant caterpillar species, also were reduced. The green cloven/vorm population decreased by 83 percent 6 days after the applica- tion. Populations of secondary pests and detritus feeders similarly were affected. Most species made a remarkable comeback and reached checkf ield levels or higher 4 weeks after treatment. The population of green cloven/vorms increased to a maximum level 2.3 times higher than in the check field during pod fill, apparently caused by decreased prédation and parasitism of eggs and early instars. Survival of the resurgent population was low, however, and few 6th instars were noted in either the treated or check fields. Percent defoliation and yield did not differ in the two fields. KEYWORDS: soybeans, arthropods, insecticides, biological control, ecology, parathion. Acknowledgments We want to express our thanks to D. A. Current, G. E. Boutz, and Barbara Campbell for their help in conducting the experiment and counting the insects. We also thank J. S. Williamson for the use of his fields. (See also abstract and acknowledgments for Soil Arthropod Fauna on page 8.) Although the research for this publication was completed ¡n the midseventies, the results are as appropriate today as when the tests were conducted. No other studies have been conducted and published that duplicate the results published here. This publicaltion reports research involving pesticides, it does not contain recommendations for their use nor does it impiy that the uses discussed here have been registered. Ali uses of pesticides must be registered by appropriate State and/or Federal agencies before they can be recommended. í/4ep44á<!¿a!e4^44¿a FOLLOW THB LABBL M.S. DtMITMINT Of AIIICVlTUlf CAUTION: Pesticides can be injurious to humans, domestic animals, beneficial insects, desirable plants, and fish or other wildlife—if they are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended practices for the disposal of surplus pesticides and pesticide containers. Trade names and the names of commercial companies are used in this publication solely to provide specific information. Mention of a trade name or manufacturer does not constitute a guarantee of warranty of the product by the U.S. Department of Agriculture or an endorsement by the Department over other pro- ducts not mentioned. Ill Contents Vegetative Fauna (Part I) 1 Introduction 1 Matehals and methods 1 Results 3 Discussion , 6 Literature cited 7 Soil Arthropod Fauna (Part II) 9 introduction 9 Study area 9 Sampling methods 9 Taxonomic list of soil arthropods collected 11 Results 13 Soil-core sampling 13 Pitfall-trapping study 17 Discussion 21 Literature cited 22 Appendix 1 23 Appendix 2 23 Issued Decembe Vegetative Fauna (Part I) Norman L Marston and Michael K. Hennessey^ Introduction flowering (R2) on August 2. We used 0.18 We took an overall sample of 15.25 Several studies demonstrate that kg Al in 7.6 L water per 0.4 ha as row-m so that we could measure ac- applications of pesticides to soybeans specified for foliar insect control in the curately the low populations, especially can have detrimental effects that may Missouri "Insect Control Recommenda- those just after treatment. The D-Vac outweigh their immediate benefit. tions" (2). The control field received no loses efficiency, however, as the bag Predators have been shown to be killed insecticide. fills with debris, and we found that such readily (4,10,22)? and chemicals disrupt Sampling Sites.—Three sampling a long sample underestimates popula- the natural epizootics of fungus sites were located in the treated field in tions. We divided each overall sample, diseases of pest species (7,9). This such a way that we could measure therefore, into 3.05-m and 12.20-m sec- often leads to resurgence of gradual recolonization of the field after tions to adjust the data for this reduced lepidopteran lan/ae to a level greater we decimated the arthropods with the efficiency and then multiplied each than that in untreated fields (15). insecticide (fig. 1). The outer plot was 12.20-m sample by a constant (C) Insecticides also may disrupt the about 60 m from the margin nearest to derived as follows: soil ecosystem. Tests show that the control field, the middle plot was 3.05 row-m sample x 4 populations of surface-active predators midway between the margin and the • ~ 12.20-m sample may be reduced (13,14), and those center of the field, and the inner plot This constant did not vary organisms responsible for the break- was at the center. One sampling site significantly among the arthropod down of organic debris may be affected was located in the control field, about groups counted (P>0.05), but it did vary aswellf72j. 120 m from the margin nearest the from week to week. (C varied from 1.35 Our objective in this study was to treated field and on a line running to 2.63, reflecting a loss of efficiency on monitor the effects of a parathion ap- through the sites in the treated field. the longer segment of 26 to 62 pet.) Data plication on arthropods. We studied all in the tables and graphs are means of aspects—plant, soil surface, and sub- D-Vac Samples—Our basic sampl- two 15.25 row-m samples (each from soil—with emphasis on the beneficial ing tool was the D-Vac.® We used an at- combined 3.05-m and adjusted 12.20-m organisms. We are reporting here the ef- tached cone (No. 304) with a distal subsamples). fect of the insecticide on arthropods on diameter of 20 cm to increase the suc- We took a pretreatment sample 3 the plants. tion at the opening (fig. 2). The cone was days before treatment. The first post- maneuvered from the bases of the treatment sample was taken 4 days Materials and Methods plants upward, then outward and down after the application in the check field We conducted our experiment in to the bases of the plants again in a cir- but was delayed by rain until 6 days 1974 in two fields, about 8 ha each, adja- cular motion as the sampler walked posttreatment in the treated field. We cent to the Missouri River 20 km slowly down each side of the row. This sampled weekly thereafter (except dur- southwest of Columbia, Mo. The soil, method insured that all foliage was ing the week of September 1 to 7 (mid- generally, is a fine sandy loam (Sarpy) sampled. R5), when we concentrated on plant- with about 2 percent organic content. We plowed, disked, harrowed, and treated the fields with a preemergence herbicide composed of 1.67 L alachlor Soybean [2-chlor-2',6'-diethyl-/V-(methoxymethyl) Check— acetanilide] and 0.45 kg linuron : Field IZZ [3-(3,4-dichlorophenyl)-1-methoxy-1- methylurea] per 0.4 ha. The fields were Uncultivated - planted to soybeans (var. 'Clark-63') on Areas ~"^^^ June 17 and 18 in 91-cm rows. Plant den- sity averaged 50 plants per 3.05 row-m at growth stage V7^ (3). The fields were cultivated twice. ! I ! I We treated one field by airplane Insecticide •Wheat- Treated Soybean with ethyl parathion [0, ikJiethyl • Field • : a<p-nitrophenyl) phosphorthioate] at full Field ^Maratón is a research entomologist, Inner Biological Control of Insects Research Unit, Agricultural Research Service, U.S. Depart- ment of Agriculture, P.O. Box A, Columbia, Mo. 65205; and Hennessey is a graduate student, Department of Entomology, P.O. Box 5215, North Carolina State University, Raleigh, N.C. 27650. ^Italicized numbers in parentheses refer FIGURE 1.—Location of sampling sites In the parathion-treated and untreated to Literature Cited, p. 7. fields, McBaine, Boone County, Mo., 1974. and any native green cloverworms on the plants on semisynthetic diet to measure incidence of parasitism and disease. Instars of the green cioverworm larvae were determined by measuring the width of their head capsules. We conducted the tests the week before we applied the insecticide and weekly for 4 weeks afterward. There were seven replications at the center of the treated field and seven in the control field. Differences between the fields on each date were analyzed by x^ tests. Plant-Shake Samples.—By mid- pod fill (Septemt)er 1 to 7), we found a resurgence of lepidopteran larvae in the treated field. We discontinued the prédation tests, consequently, and con- centrated on collecting green clover- worms to measure more accurately their populations and obtain enough live lar- BN 49356 vae to measure accurately their rate of FIGURE 2. — D-Vac machine for sampling soybean arthropods. parasitism and incidence of disease. We used a 3.05-m x 0.8-m plastic sheet stapled to wooden slats as a substrate. We slid the sheet under the shake and sweep-net sampling). Dif- plants in the row and confined within a foliage without disturbing the plants ferences between the means for each barrier designed to inhibit emigration of and unfolded it to cover the entire space site on each sampling date were tested the larvae (fig. 3). We then placed 201st tietween the rows. The plants in one row by ANOVA and Duncan's Multiple Instars and 10 4th instars on the plants.