The Natural History Journal of Chulalongkorn University 2(2): 1-5, August 2002 ©2002 by Chulalongkorn University The Short-term Effects of Atrazine Herbicide on Soil Oribatid Mites in a Mango Orchard MARUT FUANGARWORN *, CHARIYA LEKPRAYOON AND ART-ONG PRADATSUNDARASAR Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, THAILAND ABSTRACT.–Oribatid mites are a group of soil dwelling arthropods. The short-term effect of an atrazine herbicide on them was studied in a mango orchard, which had never been treated with atrazine. The experiment design was a randomized completed block (RBC) with three replications. The soil samples were randomly collected from two atrazine-treated plots (at the rates of 1,729 and 5,184 g active ingredients/ha) and a control plot. The soil sampling was done monthly and was extracted by using Berlese-Tullgren funnel. Oribatid mites density between a control plot and atrazine-treated plots were not significantly different after atrazine application in each month. Oribatid mites seem to be not affected from atrazine at both rate of application during the experimental period. KEY WORDS: herbicide; atrazine; soil fauna; oribatid mites; Thailand (Hutangkabadee and Uyvirat, 1996). It was INTRODUCTION used to control broad-leaf weeds in field crops such as corns, pineapples and in orchards. Its Mites (Acari) with the greatest abundance effects on soil fauna vary greatly from site to and diversity in most soil are the oribatid mites site due to the differences in microorganisms (Suborder Oribatida). They are usually fungi- and soil properties. This study aims to vorous or detrivorous. Through their feeding investigate the effects of atrazine on oribatid activities, they are important in the decomposi- mites in soil of a mango plantation in Ayutthaya tion process and nutrient cycling in soil province, central Thailand. (Seastedt, 1984). The use of pesticides to control insect pests and weeds may have negative effects on non-target organisms such as oribatid MATERIALS AND METHODS mites, the decomposition process and nutrient cycling may be disturbed finally. In Thailand, The experiment was conducted in an aban- the study of this effect on these animals had doned and untreated atrazine mango orchard in never been done, particularly herbicides such as Ayutthaya province. Randomized Complete atrazines. An atrazine herbicide, 2-chloro-4- Block (RBC) method was used as the experi- ethylamino-6-isopropylamino-s-triazine, ranked mental design for data processing as described third of all imported pesticides to Thailand by Rattanadakul (1978) and Cockfield and Potter (1983). The plots were 5 x 5 m2 and 3 m * Corresponding author. Tel: (662) 218-5266 E-mail: [email protected] 2 NAT. HIST. J. CHULALONGKORN UNIV. 2(2), AUGUST 2002 apart from each other. Each of two doses of The identification results were verified by Dr. atrazine, 1729 g/ha and 5184 g/ha, which is the Sandor Mahunka (Hungary). The differences of minimal and maximal recommended rates for population densities of oribatid mites between mango orchards respectively (Sangsuwan et al., plots were tested by Kruskal-Wallis test. 1984), were sprayed onto each treatment plot at the beginning of the experiment (August 1, RESULTS 2000). The control plots were sprayed with water only. The soil pH was measured by a soil The fluctuation of soil moisture, soil tester. The air and soil temperatures as well as temperature and soil pH are shown in Figure 1. the soil moisture were measured as described The differences among plots of these para- by Al-Assiuty et al. (1993). Five soil samples meters were not detected. This indicated that to depth of 5 cm were collected after 7 days of atrazine at both rates of applications may not spraying with atrazine and monthly from effect some soil properties in first four months. August to November 2000 using a soil core 6.5 In this study, 2229 soil oribatid mites were cm in diameter. The soil microarthropods were collected from the studied plots and represented extracted from soil samples by using Berlese- 16 species (Table 1). The three most abundant Tullgen funnels for 7 days and collected in 70% species were Scheloribates sp., Masthermannia ethyl alcohol. Oribatid mites were then sepa- sp. and Cyrthermannia sp., respectively. They rated, counted and preserved in 70% ethylalco- were selected to illustrate the population changes hol. Lactic acid was used to clear the specimens of oribatid mites (Fig. 2). From Table 1, the before the slide mounting. The classification number of individuals of most species and the and identification of oribatid mites were carried total number of oribatid mites in plot 1 were out according to Balogh and Balogh (1992). TABLE 1. List of collected oribatid mites in the study site and numbers of individuals (N) throughout the experimental period (Plot 1 = control, Plot 2 = atrazine minimal rate, Plot 3 = atrazine maximal rate). Plot 1 Plot 2 Plot 3 Species N Relative density N Relative density N Relative density (%) (%) (%) Sphaerochthonius sp. 78 9.01 38 4.99 44 7.32 Hoplophorella sp. 38 4.39 25 3.28 24 3.99 Epilohmannia sp. 13 1.50 13 1.71 8 1.33 Cyrthermannia sp. 90 10.39 101 13.25 48 7.99 Masthermannnia sp. 119 13.74 161 21.13 75 12.48 Hermanniella sp. 20 2.31 1 0.13 15 2.50 Berlesezetes sp. 9 1.04 12 1.57 13 2.16 Furcoppia sp. 19 2.19 4 0.52 17 2.83 Oppia sp. 38 4.39 32 4.20 16 2.66 Multioppia spp. 72 8.31 67 8.79 54 8.99 Perxylobates sp. 46 5.31 34 8.40 30 4.99 Protoribates sp. 28 3.23 17 2.23 13 2.12 Scheloribates sp. 153 17.67 107 14.04 103 17.14 Lamellobates sp. 33 3.81 22 2.89 28 4.66 Pergalumna sp 51 5.89 51 6.69 54 8.99 Rostrozetes ovulum 59 6.81 47 6.17 59 9.82 Total 866 100.00 762 100.00 601 100.00 FUANGARWORN ET AL. - EFFECTS OF ATRAZINE HERBICIDE ON SOIL ORIBATID MITES 3 control minimal rate maximum rate control minimal rate maximal rate +1)] 2.5 A 40 A mites [log(n 1.25 oil moisture (%) 123000 mean numbers of 0.015 S before 1 wk 4wk 8wk 12wk 16wk 0 1wk 4wk 8wk 12wk 16wk oSoil temperature (C) 2222256789 B mean numbers of mites [log(n+1)] 012...012555 B 24 before 1 wk 4wk 8wk 12wk 16wk 1wk 4wk 8wk 12wk 16wk 6.75 C mites [log(n+1)] 12..255 C Soil pH 5.65 mean numbers of 0.015 before 1 wk 4wk 8wk 12wk 16wk 1wk 4wk 8wk 12wk 16wk week(s) after atrazine application week(s) after atrazine application FIGURE 2. Mean individual numbers of three selected FIGURE 1. The fluctuation of soil moisture (A), soil oribatid mites species (transformed data and standard error): temperature (B), and soil pH (C). (A) Scheloribates sp., (B) Masthermannia sp., and (C) Cyrthermannia sp. highest, followed by plot 2 and plot 3. Although this showed a tendency of a reduction of oribatid mites numbers under the application of atrazine, DISCUSSION but there was no significant difference (Kruskal- This study did not detect an effect of Wallis test, p > 0.05) in the abundance of each atrazine on oribatid mite populations in a man- species (Fig. 2) and of total oribatid mites (Fig. go orchard. The nil effect of this herbicide on 3) between plots. However, we noted that there soil microarthropods (Acarina and Collembola) was different pattern in their population density were also reported in maize fields (Popovici et changes. The density of Scheloribates sp. and al., 1977; Fratello et al., 1985). There may be Masthermannia sp. seemed to be less fluctuated save to oribatid mites when atrazine at the (Fig. 2A and 2B), but Cyrthermannia sp. gra- recommended rates were applied. However, dually declined through the experiment period atrazine persisted for more than six months (Fig. 2C). 4 NAT. HIST. J. CHULALONGKORN UNIV. 2(2), AUGUST 2002 control minimal rate maximal rate 4 )]1 + n 3 g( o s [l e mit 2 of r e b m nu 1 n a e m 0 before 1 wk 4wk 8wk 12wk 16wk week(s) after atrazine application FIGURE 3. Mean number of oribatid mite individuals (transformed data and standard error) sampled before and after the application of atrazine. (Luangarpapong, 1998) and oribatid mites have Scheloribates sp. their population tend to be little capacity to respond numerically to the stable as well. Behan-Pelletier (1999) suggested short-term environment alteration such as toxic that many species in this genus are drought- impact (Lebrun and Van Straalen, 1995). The tolerant ubiquitous species. They have a world- long-term effect of atrazine should be studied wide distribution (Balogh and Balogh, 1992). since its metabolites may affect soil organisms. In addition to the direct effects of atrazine, ACKNOWLEDGMENTS oribatid mites could be affected indirectly by a reduction of the herbaceous layer (Curry, 1994) We would like to express our thanks to Dr. where is their food sources, organic matters. Sandor Mahunka who verified the identification Although some weeds were excluded by atra- results and kindly provided a useful key of zine, in this study, the major sources of organic oribatid mites, to the owner for his generous matters were mango trees. assistance at the experimental sites. M.F. Although the effect of atrazine on oribatid especially thanks Mr. Thongchai Ngamprasert- mites was not found, the population change of wong and Miss Orawan Duangpakdee for their selected species are noted that there are differ- encouragement and many suggestions. This ent trends. Cyrthermannia sp. of the family study was financially supported by Faculty of Nanhermanniidae declined at the end of the Science Chulalonglokorn University and the experiment (Fig. 2C) with the reduction of soil Development and Promotion for Science and moisture (Fig. 1A) since the attractive environ- Technology Talents Project (DPST) to M. F. ment of Nanhermanniid mites is high humidity (Behan-Pelletier, 1997). Masthermannia sp., however, is in the same family of Cyrtherman- LITERATURE CITED nia sp. but their population seems to be more stable. They may tolerate to drought condition Al-Assiuty, A. I. M., B. M. Bayoumi, M. A. Khalil more than Cyrthermannia sp. One of the most and N. M. Van Straalen. 1993. The influence of abundance oribatid mites in this study is vegetational type on seasonal abundance and FUANGARWORN ET AL. - EFFECTS OF ATRAZINE HERBICIDE ON SOIL ORIBATID MITES 5 species composition of soil fauna at different Hutangkabadee, B. and A. Uyvirat. 1996. 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