193499b0Nature1934814196202034995010028-0836196210.1038/193499b0ukNatureNatureNATUREnatureNature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public./nature/journal/v193/n4814issueJournal homeArchiveCurrent issueAdvance online publicationPrivacy policySubscribeNature Publishing GroupCurrent issue193499b0Resistance to Dieldrin of Cimex hemipterus (Fabricius)
AU  - ARMSTRONG, J. A.
AU  - BRANSBY-WILLIAMS, W. R.
AU  - HUDDLESTON, J. A.Tropical Pesticides Research Institute, Arusha, Tanganyika.[ast]Present address: Department of Biological Sciences, Queen's University, Kingston, Ontario, Canada.THE first report of resistance to dieldrin by the tropical bed-bug, Cimex hemipterus, in East Africa was that by Smith1. In observations made during the course of the Pare-Taveta Malaria Control Scheme, it was reported2 that the bed-bug population was reduced to very low numbers following the first dieldrin spray (first treatment of 80 mgm. dieldrin/sq. ft. followed by subsequent treatments of 40mgm./sq.ft. at eight-month intervals), but 14-19 months after this treatment the bed-bugs were present in sufficient numbers to be considered of nuisance value. In a series of laboratory tests it was shown that whereas bed-bugs from an untreated area were all dead after a seven-day exposure to 0.1 per cent dieldrin using a method suggested by Busvine3, there was only an 18 per cent mortality for a similar exposure time among bed-bugs from the treated area.Table 1. PERCENTAGE MORTALITIES OF Cimex hemipterus FROM TREATED AND UNTREATED HOUSES AFTER EXPOSURE TO DIBLDRIN IMPREGNATED PAPERS FOR 2 HR.
Source of material
Untreated houses Treated houses
0-05
0-10
Concentration of dieldrin 0-20 0-40
0-80
Control
3-4(204)0-0(91)[ast]4-3(133)3-9(184)12-3(211)23-0(198)
5-0(201)0-8(105)8'0 (96)13-0(169)4-4(143)10-7(105)
Corrected percentage mortality with the number of insects tested shown in parentheses 
In March 1958 a group of experimental ant-proof houses was constructed at Magugu and treated with dieldrin for the purpose of assessing the field performance of dieldrin/resin wettable powders on sorptive surfaces4. The only way that a non-flying insect could enter the houses was to be carried by people working in the houses. Six months after treatment, complaints were received of the presence of bed-bugs in some of the houses,
Adult bugs were collected from the dieldrin-treated houses and from non-treated houses in the village and exposed to a series of concentrations of dieldrin using the World Health Organization adult mosquito test kit. Since it was desired to obtain comparative data on the susceptibility of bed-bugs from treated and untreated houses, the bugs were exposed for only 2 hr. and then transferred to untreated holding tubes for a further 24-hr. period, after which time the percentage mortality at each concentration was calculated. Over a period of approximately 18 months, with teats carried out at monthly intervals, there was no sign of a measurable increase in resistance once the degree of resistance had been established, although there were slight month-to-month variations in the tests with both the resistant and the susceptible bed-bugs. The results of these tests were grouped as being from treated or untreated houses and are shown in Table 1.
A complete probit analysis5 of these results was made, and the following equations for the dosage-mortality lines were obtained: untreated houses (susceptible bed-bugs) Y = 0-4651 + 2-1190;c (Fig. 1, line [pound]5) ; treated houses (resistant bed-bugs) Y = 3-0073 + 0-4487& (Fig. 1, line #5).
The significance of the change in slope ('6' value in the equation) of the line and also the lateral displacement (V value in the equation) of the line has been discussed by Hoskins and Gordon6. It was shown that a change in the lateral displacement of the lino, with no change in the slope, is indicative of a change in the vigour tolerance of the insect and not of the development of true resistance. However, where there was a marked change in the slope of the line from a relatively steep slope (large value of '&') to a relatively shallow slope (small value of '6'), with a possible change in the displacement of the line, true resistance is said to have occurred. The information obtained in the tests at Magugu shows the presence of resistant C. hemipterus in the dieldrin-treated houses and the small variations which occurred in the monthly tests of both the resistant and susceptible bed-bugs are attributed to experimental variations and changes in vigour tolerance of the different groups sampled.
99
K[ast]Jt
I 90
o
[dollar] 70 | 50 I 30
10
1 -
0-0125
0-05
0-20
0-80
3-2
Concentration of dieldrin (per cent)
Fig, I, 81, Kwasunga (susceptible, 5-day exposure, 0-day holding period); 6'2, Hong Kong (susceptible, 5-day exposure, 0-day holding period); SB, Mogadiscio (susceptible, 5-day exposure, G-day holding period); [dollar]4, Magugu (susceptible, 5-day exposure, 0-day holding period); Sb, Magugu (susceptible 2-hr, exposure, 24-hr, holding period), Rlt Pare (resistant, 14-day exposure, 0-day holding period); R2, Pare (resistant, 1-day exposure, 12-day holding period); J?3, Pare (resistant, 10-day exposure, 0-day holding period); Ji4, Pare (resistant, 7-day exposure, 0-day, holding period); JK5, Magugu (resistant, 2-hrs exposure, 24-hr, holding period); RQ, Pare (resistant, 1-day exposure, 7-day holding period)
A similar probit analysis was carried out on the test results quoted by Busvine7 and Smith1. Through the courtesy of Dr. A, Smith (personal communication), we were also permitted to analyse the test results of his preliminary observations on bed-bug susceptibilities carried out in the Pare-Taveta area. In those tests the bed-bugs had been exposed to a series of dieldrin concentrations for periods ranging from a one-day exposure with a seven-day holding period to a fourteen-day exposure with no holding period. In each case a control test with untreated papers and with the test insects exposed for identical periods of time had been set up. A complete probit analysis of these corrected tests was made and the dosage/mortality lines were plotted (Fig. 1). At this time bod-bugs were collected from the untreated houses at Magugu (the treated houses having been dismantled, no more resistant bugs were available) and exposed to dieldrin for a five-day period (Fig. 1, line [dollar]4). Although this line, [dollar]4, is displaced from [dollar]5 due to the increased exposure time, the slopes of the two are practically the same.
Within the susceptible and the resistant groups there is, in spite of the fact that the tests were carried out by different people on different populations of bed-bugs and at varying lengths of exposure and holding time, a marked similarity in the equations of the lines. This similarity shows up clearly when the plots of the dosage/mortality linos are examined, and it is seen that there are two definite groups of results, those of the susceptible bed-bugs and those of the resistant bed-bugs. An examination of the equations of the lines shows the following: (1) In all susceptible bed-bug tests, the slope of the line is always greater than 2-0 and there is, at most, a two-fold variation from flattest to steepest slope; (2) in all resistant bed-bug tests, the slope of the line is never greater than 0[ast]8 and again there is only a two-fold, variation in the slopes.
Thus it appears that among all O. hemipterus tested there is a marked consistency in their genetical composition with respect to the genes of chromosomes associated with dieldrin resistance, and it is suggested that use may be made of this in determining resistance to dieldrin among populations of C. hemipterus. If it were true that all susceptible C. hemipterus, when exposed to a series of dieldrin concentrations ranging from 0-05 to 1-6 per cent for any period, will give mortalities found on a line in which the slope is greater than 2-0, and that all resistant C. hemipterus, when exposed to a similar range of concentrations for an identical time, will give mortalities which when plotted will give a line with a slope less than 0-8, then to determine the presence or absence of resistance it would be necessary to collect and test only sufficient bed-bugs to plot a single line from which the slope could be calculated.Smith, , A., Bull. World Health Org., 19, 1124 (1958).Pare-Taveta Malaria Control Scheme (East Africa High Commission, 1960).Busvine, , J. R., and Nash, , R., Bull. Ent. Res., 44, 371 (1953).ISIChemPortvan Tiel, , N. (in the press).Finney, , D. J., Probit Analysis, second ed. (Cambridge University Press, 1952).Hoskins, , W. M., and Gordon, , H. T., Ann. Rev. Ent., 1, 89 (1956).ISIChemPortBusvine, , J. R., Bull. World Health Org., 19, 1041 (1958).ChemPort