UFDC Home  Search all Groups  World Studies  Federal Depository Libraries of Florida & the Caribbean  UF Government Documents Collection  Vendor Digitized Files   Help 
Material Information
Record Information

Full Text 
LIB"R ARY 'ATE PLANT BOARD UtMEK 0Bft3X =KA 9 MI O AGBICULTMB Agricultural Researoh Admalnistration ureau of ontology and Plant Quarantine E T 0 53W SISoSIoIC ACTION OF I CTICIDMs AID A SOWT CT IN ANALIBIS By F K. M.Vadley, statistical consultant he purse of this paper i1 threefold: (1) To restate definitions of Joint action of insecticides, (2) to show what is required for clear cut recognition of synergisma, and (3) to indicate a workable abshort cut in analysis. Definitions Synengm between insecticides m be defined as a joint action of two materials, such that the total effect is greater than the sum of the two effects when each is used alone. Cox (2) restricts the application of the tera "aynergism" to mixtures of insecticidal materials, each of which has some toxicity when used alone. He thus excludes the case where a substance without toxicity of its own i mproves the action of an insecticide. Such a substance Is called simply an activator. The proof of activation is less oaoUlex than that of synergism; a significant added percentage 6f kill shown in replicated trials should be sufficient. To u terstad syInergism it is necessary to consider possible types of action of Bmixtures of poisons. The subject has been discussed clearly by Bliss (_) a inn ) ad touched upon by the writer (2). Bliss discusses three types of action of two poisons in a mixture independent joint action, similar joint action, and synergistic action. Both Bliss and Finney mention the possibility of negative synergisma, or antagonism, and both suggest methods for analysis of data on toxic action. The methods discussed may be extended to mixtures of more than two poisons. Iaen action can be defined as action in a different way by each poison, a different physiological activity or vital system being affected.. There my be more or less correlation in susceptibility, since the Individuals susceptible to one action um tend also to be susceptible to the other. If there is a marked positive correlation of this sort, both poisons will tend to work on the sow group of insects, and we will get little or no increase in kill by the mixture over the mortality that would be caused, by the stronger insecticide used alone. AUG 1 3 9 If there is little or no correlation, there will be no kill by each substance and seom overlapping, of the sort indicated by Abbott's forila for am mortality in the presence of another. In that case the total kill will be higher than it would be with correlation. The possibility of negative correlation, that is, the individuals suscep "tible to one poison being resistant to the other, might also be con sidered. Zach poison would kill the group susceptible to it with little or no overlapping, and the total kill would be still higher. This aon dition seem unlikely. Finney defines expected independent action vith out allowance for correlation. This is equivalent to the concept of Abbott's formula. Suppose, for instance, that a certain concentration of poison A kills 80 percent and one of B 60 percent. If the two poe sons are independent in action, we would expect a kill of 80 percent + 60 percent(60 percent of 80 percent), or 92 percent. It seemS probable that soe positive correlation often occurs. Action significantly less than independent action indicates antagonism. Similar Joint effect is produced by two or more poisons acting similarly, and affecting the same organs or processes in the indivldnal. It Implies that one insecticide could be substituted for the other at a constant rate. If this rate is known, equivalence can also be determined. It is recognized that the soundest method of comparing two itsecticides is to ovare concentrations needed for a given effect, and this mthod has a special application here. Suppose, for instance, that a concentration of 1 unit of insecti cide A is required to give 50 percent kill of an insect species, and that 2 units of insecticide B are required for the sam result. Than A is twice as effective as B. A mixture of 1/2 unit of A and 1 unit of B will produce the ano result as either 1 unit "of A o 2 of B, if similar Joint effect occurs. If action is independent, there will be som overlapping, and the =ixture will have somavwhat less effect. On the basis of similar Joint effect, 1 unit of A and 1 of B will be equivalent to 1 1/2 units of A alone. It can readily be shown, by the nature of dosagemortality curves involved and the slopes they usually show, that similar Joint effect is greater then independent effect, either with or without correlation. The greatest effect of a mixture, which could be predicted from idi vidual action of its ingredients, would be similar Joint effect. If the effect of the combination can be shown to exceed sianflioantly the action expected froa similar Joint effect, synergism is strongly in dicated. The Determination of Synergism The determination of synergism will require (1) sam estimate of similar Joint effect inferred from the action of each ingredient used alone, and (2) the determination of significance of erperiority in re sults, if any, over this similar effect. To estimate the similar Joint effect we need dosagemrtality curves for each poison alone, so that equlvalecoe n.t a given mortality can be calculated by interpolation. The log;rotl transf zamtic is 3 convenient for this purpose, since it usually gives linearity between 40 and 95 percent mortality, and since special logprobability paper can be obtained for rapid graphic interpolation. As a matter of fact, between 25 and 70 percent the untransformed dosagemortality curve is near enough linearity for rough interpolation, but above 70 percent the transformation ie an improvement. When the estimate of equiv alence has been obtained., the concentration of the mixture can be calculated in terms of either constituent, and expected similar Joint effect can be read off the dosagemortality curve for the constituent chosen. Thla predicted effect can be compared with the actual. It li desirable also to have a dosagemortality curve for different con centrations of a mixture of given proportions. This is not essential, however, for preliminary determination, if one concentration that will cause mortality between 50 and 90 percent is available. Results with this me concentration of a mixture, if adequately replicated, aW be compared with calculated Joint effect derived from veil determined dosage mortality curves of individual materials. The com parison involves the determination of stignificance, the second step mentioned. Significance is basically determined from consistency. Finney(Q) discusses methods of determination of significance; the author, in the next section, suggests a simple method. To determine the equivalence, similar lopes in both dosage mortality curves ust be assumed. This is a fairly safe assumption for poisons of similar Joint effect. In limited bxperimhntC slopes are not likely to differ significantly, and a cou.on s W uay be derived and used. If slopes realLU differ. equivrlance will wj at different points. This condition may occur and add to complexity in some cases where action is independent; it seems unlik ly that synergism will be found under such conditions. 7izmq (1) gives a good exposition of methods of calculation, using data from an article by Martin (4) in the same Journal. Finney illustrates the calculation of equivalence from logprobit dosage mortality curves for a mixture for each ingredient, with common slope, and the statemnt of concentration of a mixture in terms of one of the substanes involved. A dosagemortality equation can then be written for the mixture, using the equation for that ingredient in terms of which the mixture is stated. The dosage giving 50 percent mortality (LD. 50), or any other mortality level desired for com parison, can be readily calculated, Finney (.) outlines a chisquare test to compare the actual effect of a mixture iOilth that expected from either independent or similar Joint effect. He also cites a rather complex fazulla for standard error of difference of L. D. 50 of a mixture from predicted L. D. 50 on a jointaction basis. Calculations are based on statistical methods developed for probit analysis. ShortCut Procedures Much time m be saved in getting a preliminary determialnation of equivalence by shortout methods, using logprobability paper and pgraphic determinations. For example, we my take the date of Martin used by Finney On the effects of rotenone and deguelin on an aphid, Macroslphoniella sanborni (Gill). Sam results obtained over a range of toxicity aited to the problems are tabulated as follows: Botenone Concentration ME./liter 3.8 5.1 7.7 10.2 Percent 33.3 52.2 85.7 88.0 Deguelin I Concentration Percent 37.5 70.8 95.9 10.1 20.2 30.3 40.4 The data given above are plotted on logprobability paper (fig. 1), and eyfitted lines are drawn. A reading taken from these lines at 50 percent ehovs that 13.2 units of cZ.lin are required to equal 4.8 of rotenone, or that deguelin is about 0.36 as toxic as rotennce. At the 90 percent level 9.7 units of rotenone appear to equal 28.0 of deguelin, giving deguelin an equivalence of 0.35. The average is 0.355 (Finney's ooquted value is 0.37). According to Martin, the mixture of rotenone ari deguelin gave the results shown In table 1. Table l.The actual and the interpolated mortality obtained vith a mixture of rotenone and deguelin of given concentrations Rotenone concentration Deguelin concentration Rotenone equivalent  Actua Mortality g./liter M./lter Percent Percent 1.0 4.1 2.5 47.8 11.2  2.0 8.1 4.9 58.7 = 5.0 51 3.0 12.2 7.3 79.2 10.2 78 4.0 16.3 9.8 93.5 2.9 90 Y Rotenone + 0.355 deguelin. / See fig. 1. Interpolated  5  By using the "rotenonb equivalentO as concentration, the expected Joint effect can be read off from, the eyefitted rotenone line. For instance, with equivalent of 7.3 the expected kill is read as 78 per cent. It will be shown at each point that the actual is somewhat greater than the estimated effect, but the estimated effect conme within 1 or 2 standard errors of the actual. More exact calculation will give a little better results. The estimated, as vell as the actual, values have calculable standard errors, which decreases the tendency to significant differences; on the other hand, the fact that all dif ferences are in the samen direction will increase this tendency. The conclusions of Finney are the same as have been reached by the shorter method in a few minutes work. mixture tends to produce an effect exceeding Joint action, but this tendency does not reach significance. The other cases treated by Martin and Finney have been studied in the same vay. Working as above, the author calculated a rotenone equivalent of 0.215 for elliptone, as compared with Finney 0.20. For toxicarol the equivalent calculated is 0.175, as compared with Finney's 0.16. The conclusions as to synergism, arrived at by the rapid method were the sam as those reached by Finney by the more complex =athe mtical mthod. Dosagemortality curves from replicated experiments would afford opportunity for several independent determinationsm of equivalence, and of expected mortality from a mixture. The latter could be used in calculating a standard error. With error estimates for both calculated and actual effects, the error and significance of the difference could easily be calculated. Sumury The author defines the types of Joint action of insecticides com bined in a mixture. He then ose that, in order to prove the exis.a tence of synergism, the effect of the mixture must be shown to be significantly greater than the maximmnn effect predictable from separate actions of the insecticides. This maxlmm is given by assumption of similar joint effect. Dosagemortality curves for separate ingredients =y be used to estimate equivalence and expected similar Joint effect. Replicated trials with a mixture my be used for comparison with the estimated effect. A muchshortened graphic procedure will give results of practical value. In many cases the type of action produced by a mixture will not be exactly determinable from results, but a clearcut superiority over a calculated similar Joint effect will indicate synergism. Literature Cited (1) Bilss, C. I. 1939. The toxicity of poisons applied Jointly. Ann. Appl. Biol. 26: 585615. (2) Com, A. J. ]943. Terminology of insecticides, fungicides, and other economic poisons. Jour. Econ. Ent. 36: 813821. (3) nuy, B. J. 1912. The almtpli of toaioity teot on Rixturu of ptoiMs, Am. Appi. aol. 299l 829. (4) Martin, J. T. 9Wo1 The problem of the eraatloam oaloulatlM of rotnamoooi talning plants (VI). Ann. App. Blol. 29: 6981. (9) Vad]A, F. M. 143. Statistical aspect. of labtratoy Amer. Assoc. Mv. Sgo. Pab. 20: teots of Insotoid,. 177188. W LOG.PROBABILITY INTERVALS (FOR DOSAGEMORTALITY ETC.) 99,8: 99. 5      .. . .. ..... .. ..... I f 1 1  .^  2 9.0 _      . ... fl n   .. ... . sMii  :f 1111! __ n 13 11 0i. 70.0 Lii II WU5. . 60. U. 5 5 .0 0i hi 50.0 45.0 40.0 z 30.0 WJ 2& 0 .. . nM 2oD. I1. ,====0 EEEi lEi iiiiiiii 10.0 5.0  zo mi 1.5 2.0 2.5 3.0 Hill I I 4JD 15.0 200 250 300 400 CONCENTRATION Figure l.The percentage of mortality obtained with several concentrations of rotenone and deguelin, plotted on logprobability paper. Dots indicate rotenone; crosses, deguelin. 03 0 * ;;; ;;;;;;;;4 " UNIVERSITY OF FLORIDA 11111l iiI11111111111111111I IM111 LItill 111111111111 1 3 1262 09240 8698 