The influence of temperature on the susceptibility to eight organophosphorus insecticides of susceptible and resistant strains of Tribolium castaneum, Oryzaephilus surinamensis and Sitophilus granarius

J. \mrni Prod. RF\. Vol. Printed m Great Britain

18, pp

0022.474X/SZ/OlOOl3-07103.00 0 Pergamon Press Ltd

13 to 19. 1982

THE INFLUENCE OF TEMPERATURE ON THE SUSCEPTIBILITY TO EIGHT ORGANOPHOSPHORUS INSECTICIDES OF SUSCEPTIBLE AND RESISTANT STRAINS OF TRIBOLIUM CASTANEUM, ORYZAEPHILUS SURINAMENSIS AND SITOPHILUS

GRANARIUS

P. S. TYLER and T. J. BINNS* Ministry of Overseas Development, Tropical Stored Product Centre; *Ministry of Agriculture, Fisheries and Food; London Road, Slough, Berkshire, England (Accepted

19 August 1981)

Abstract-Susceptible strains of adult Tribolium castanem, Oryzaephilus surinamensis and Sitogranarius were exposed for 24 hr to a range of deposits (from 10 to 5000 mg/m’) of eight organophosphorus insecticides (bromophos, chlorphyrifos-methyl, fenitrothion, jodfenphos, malathion, phoxim, pirimiphos-methyl and tetrachlorvinphos) at 10, 17.5 and 25°C. Based upon knockdown and kill, the effectiveness of all insecticides was greater at 25°C than at 17.5”C and was markedly lower at 10°C. At 10°C tetrachlorvinphos, bromophos and jodfenphos were virtually ineffective to S. granarius even at 5OOOmg/m*. By contrast at 25”C, lOOmg/m’ was adequate to give complete knockdown of all species with most insecticides, the exceptions being malathion and tetrachlorvinphos. The three most effective insecticides, chlorphyrifos-methyl, pirimiphos-methyl and fenitrothion were also tested, in comparisbn with malathion, against a known malathion-resistant strain of each of the test species. Chlorpyrifos-methyl and pirimiphos-methyl were the most effective materials against both susceptible and resistant strains of all species. Knockdown was inevitably followed by mortality although at the lower temperatures this took several days.

philus

INTRODUCTION THE OPTIMUMtemperature for the development of many stored-product beetles is about 30°C (HOWE, 1965). The most popular temperature for laboratory evaluations of insecticides appears to be about 25°C. In practice, however, many treatments against infestations in temperate regions are applied at 1&2O”C. At these lower temperatures, the insects are less active but the requirement is for a rapid, lethal effect. The object of this study was to obtain comparative data on the effectiveness of eight organophosphorus insecticides at 25, 17.5 and 10°C. The three species selected for the tests were Tribolium castaneum (Herbst), Sitophilus granarius (L.) and Oryzaephilus surinamensis (L.). All are major pests of stored products and insecticide resistance has been confirmed in strains of each. Consequently malathion-resistant strains of all three were included in some tests. MATERIALS AND METHODS Details of the insect strains (all of which were reared at 25°C and 70% r.h.) are as follows. Tribolium custaneum (culture medium, wholemeal flour) and 0. surinumensis (culture medium, 5 parts wheatfeed; 5 parts rolled oats; 1 part yeast) were tested when 3-5 week old adults. Sitophilus grunurius (culture medium, whole wheat) was tested as 24 week old adults. The susceptible strains had been in laboratory culture for many years without exposure to insecticides. The resistant strain of S. grunurius (SG12) was collected from a flour mill in Victoria, Australia and the resistant strain of 0. surinumends came from Israel. Both were collected during the FAO Global Survey on insecticide resistance and were found to be resistant to malathion and other insecticides (CHAMP and DYTE, 1976). The resistant strain of T. custuneum (CTC-12) was collected from Queensland and was the strain studied by CHAMP and CAMPBELL-BROWN (1970). This strain was also resistant to malathion and other insecticides. The eight insecticides 13

14

P. S. TYLER and T. J. BINNS

used were commercial formulations of emulsion concentrates and were bromophos 385 g/l, chlorpyrifos-methyl 240 g/l, fenitrothion 500 g/l, jodfenphos 200 g/l, malathion 600 g/l, phoxim 600 g/l, pirimiphos-methyl 250 g/l and tetrachlorvinphos 240 g/l. A range of solutions was prepared by serial dilution with distilled water from a stock solution to give concentrations for a range of deposits from 10 to 5000 mg/m’ of active ingredient per 7 cm dia filter paper. The range of concentrations used in each test was selected according to the susceptibility of the test insects. The solutions were applied in 0.5 ml aliquots pipetted evenly over the surface of each paper. Three replicate papers were tested for each species at each concentration. The treated papers were placed on glass sheets to dry and a fluon-coated glass ring, 6 cm in dia and 2 cm high, was stood on each paper. The treated papers were allowed to dry overnight at 25°C and then were placed at the appropriate exposure temperature. The beetles were counted into batches of 25 and confined without food in glass tubes which were placed in a constant temperature and humidity (CTH) room for exposure the next day. The insects for tests at 25 and 17.5”C were placed immediately in CTH rooms at the required temperature, but those for treatment at 10°C were first placed in a room set at 17.5”C for 5 hr and then moved to a 10°C room. This procedure for acclimatization was adopted to avoid sudden chilling. The batches of beetles were tipped on to the treated papers the following day; control insects were placed on untreated papers. Exposure was continued for 24 hr after which the insects treated at 10 and 17.5”C were transferred to 25°C and left for an hour to equilibrate the activity of the three groups of insects, After this period the number of knocked-down and live insects were counted. A knocked-down insect was one which had lost the ability to coordinate its movements and was lying on its back. An insect was considered to be dead when, under a low power microscope, no movement could be observed even after prodding with a fine brush. Some tests with chlorpyrifos-methyl and malathion differed slightly as follows. Observations were carried out over a period of 5 days to establish the relationship between knockdown and kill. Two or three replicates of 25 insects were used at 25°C plus 4 to 6 replicates, each of 25 insects, at 17.5 and 10°C. A small amount of kibbled wheat was placed on each paper to serve as food. After 24 hr continuous exposure half the replicates at 10 and 17.5”C were moved to 25°C for acclimatization before counting. The number of knocked down and live insects was then recorded and these insects were discarded. The remaining batches at 10 and 17.5”C were moved to 25°C after 5 days and the number of dead beetles was recorded. The 25°C test was also examined after 24 hr and again at 5 days. All post-treatment exposures were at 70% r.h. RESULTS

The results obtained for the knockdown responses are shown in Tables l-3. The relationship of knockdown with kill after 5 days is presented as histograms in Figs 1 and 2. There was no knockdown in the controls for any species or strain after 24 hr exposure. Correction for control mortality has been made for 0. surinamensis, where, after 5 days, mortality did not exceed 8%. There was no mortality with either 7: castaneum or S. granarius. DISCUSSION

The approximate dosages in mg/m2 recommended by the manufacturers for each insecticide are: bromophos 500; chlorpyrifos-methyl 100; fenitrothion 500; jodfenphos 1000; malathion 800; phoxim 100; pirimiphos-methyl 200; and tetrachlorvinphos 1250. Only chlorpyrifos-methyl was effective at 10°C at this dosage. Against susceptible T. castaneum at 25 and 17.5”C the recommended dose was effective for all insecticides except malathion. Chlorpyrifos-methyl was also the only insecticide completely effective against the resistant strains at all 3 temperatures. Against susceptible 0. surinamensis all insecticides were effective at 25 and 17.5”C within the recommended dosage rate. Only pirimiphos-methyl and fenitrothion were also effective at 10°C. With resistant 0. surinamensis, chlorpyrifos-methyl and pirimiphos-methyl were effective at the recommended

15

The influence of temperature on insecticides TABLE ~.THE INFLUENCEOFTEMPERATUREONTHE OF

SUSCEPTIBILITYOFSUSCEPTIBLE(S)AND

MALATHION-RESISTANT(R)STRA

~riho/iumcasraneum

TO EIGHTORGANOPHOSPHORUSINSECTICIDES.(F~GURESREPRESENT PERCENTAGEOF BEETLES KNOCKED DOWN AFTER 24hr CONTINUOUS EXPOSURE AT THE STATED DOSAGE AND TEMPERATURE)

Insecticide

Strain s

Temperature (“CJ

10

50

25 17.5 10

100 100 13

100

25 17.5 10

100 40 7

100 95

25 17.5 10

40 0

100 100

25 17.5 10

8 0

25 17.5 10

32 0

25 17.5 10

10 2

100

500

Deposit in mg/m’ 1000 1500 2000

3000

4000

5000

84

98

100

100 76

88

98

100

0

70

90

0 0

4 2

12 4

20 6 0

4

4

4

8

Chlorpyrifos-methyl R

S

100

0

95

100

98 32 0

100 98 42

100 58

80

0

17

82

100

68 62 4

100 84 4

94 16

98 26

0 0

75 8

100 28

100

Pirimiphos-methyl R

S

74 18

100 100

Fenitrothion R

S

16 12 0

25 17.5 10

Malathion

Phoxim

Tetrachlorvinphos

R

25 17.5 10

S

25 17.5 10

40 0

25 17.5 10

0 0 0

S

loo 100 0

72

94

100

22 24 14

92 96 44

100 100 98

96

100

Bromophos

S

25 17.5 10

92 0

100 12

56

100

Jodfenphos

S

25 17.5 10

96 3

100 49

75

83

100 0

dosage at 25 and 17.5”C. However, even at double the normal dosage both failed to affect resistant insects at 10°C. Excluding the unimpressive performance of tetrachlorvinphos, all insecticides were effective at the recommended dose against susceptible S. granarius at 25°C. At 17.5”C bromophos and jodfenphos were ineffective and phoxim marginally so. At 10°C only chlorpyrifos-methyl was effective at the recommended dose. The resistant strain was affected at 25°C by chiorpyrifos-methyl, fenitrothion and pirimiphos-methyl; at 17.5”C pirimiphos-methyl failed and at 10°C only chlorpyrifos-methyl was effective. Overall, chlorpyrifos-methyl emerged as the most effective insecticide tested. This conclusion concurs with earlier work (TYLER and BINNS, 1977) where chlorpyrifos-methyl was rated best against 18 species of stored-product beetles.

16

P. S. TYLER and T. J. BINNS

The limited tests with chlorpyrifos-methyl and malathion carried out to examine the relationship between knockdown and kill (Figs 1 and 2) showed that, at the highest temperature, 100% mortality at 5 days followed the 100% knockdown recorded at 24 hr in 50 of the 51 situations. However, as the temperature is lowered mortality is reduced so that even with the most effective insecticide, chlorpyrifos-methyl, although knockdown was achieved by 24 hr at lO”C, negligible kill had occurred after 5 days. The results show a marked decrease in the effectiveness of all insecticides tested with a lowering of temperature. This difference may be related to the lowered activity of the beetles observed at low temperatures although other factors, such as a slower penetration of insecticide through the cuticle and less rapid internal transport of the insecticide to the site of action may also reduce effectiveness at lower temperatures. Positive correlations of temperature with effectiveness for organophosphorus insecticides have been noted in laboratory tests by ZWICK (1962) using malathion at 21 and TABLE~.THEINFLUENCEOFTEMPERATUREONTHESUSCEPTIBILITYOFSUSCEPTIBLE(S)AND MALATHIONRESISTANT(R) STRAINS OF Sitophilus granarius TO EIGHT ORGANOPHOSPHORUS INSECTICIDES.(FIGURESREPRESENT PERCENTAGE OF BEETLES KNOCKED DOWN

AFTER 24hr CONTINUOUS

EXPOSURE AT THE STATED DOSAGE AND TEMPERATURE) Deposit in mg/m’

Temperature

Insecticide

Strain

S

( Cl

10

50

100

25 17.5 10

100 100 56

98

100

25 17.5 10

97 25 3

100 100 73

83

100

25 17.5 10

47 0

100 70

85

100

25 17.5 10

0 0

25 17.5 10

100 42

25 17.5 10

20

500

1000

1500

2000

0

82

100

100 0

6

18

0

7

17

57 5

97 30 0

100 67 5

loo 100 88

100

0

100 0

3000

4000

5000

36

60

66

78

22

67

98

100

82 4

94 6

100 10

20

22

17

2

2

14

30

58 0 0

10

32

60

86

100

Chlorpyrifos-methyl R

S Pirimiphos-methyl R

S

98 28

loo 88

100

Fenitrothion R

S

42 0

25 17.5 10

0 0 0

Malathion

Phoxim

R

25 17.5 10

S

25 17.5 10

2 0

100 14

54

0

Tetrachlorvinphos

S

25 17.5 10

Bromophos

S

25 17.5 10

100 2

2

7

51

100

S

25 17.5 10

0

Jodfenphos

0

13

25

15 10 0

15

20

40

42

68 0

0

10 0

14 2

48 10

86 48

17

The influence of temperature on insecticides

TABLE 3. THE INFLUENCEOFTEMPERATUREON THE SUSCEPTIBILITYOF SUSCEPTIBLE (S)AND MALATHION-RESISTANT(R) STRAINS OF Oryzaephilus surinamensis TO EIGHT ORGANOPHOSPHORUS INSECTICIDES.(FIGURES REPRESENT PERCENTAGE OF BEETLES KNOCKED DOWN AFTER 24hr CONTINUOUS EXPOSURE ATTHE STATEDDOSAGE ANDTEMPERATURE)

Deposit in mg/m’

Temperature Insecticide

Strain

(“Cl

10

50

100

500

S

25 17.5 10

97 48 0

loo 100 67

93

100

25 17.5 10

95 92 42

100 95 77

100 85

97

25 17.5 10

100 100 0

75

75

100

25 17.5 10

48 2 0

84 56 36

86 86 42

100 100 80

25 17.5 10

100 100 30

70

98

100

25 17.5 10

74 0

74 72 0

82 78 74

25 17.5 10

0 0

80 93

25 17.5 10

10

R

S

25 17.5 10

72 18 0

1000

1500

2000

3000

4000

5000

100 94 68

96 68

Chlorpyrifos-methyl R

S

100

Pirimiphos-methyl R

S

92

92

96

100

90 82 76

92 92 82

100 100 92

98

100

100 100 0

17

100

17 25 0

55 32 7

77 65 20

80 62 36

82 62 46

94 90 56

100 100 22

90

loo

0 0 0

14 6 2

98 94 40

100 100 78

70

86

100

100 0

7

15

21

47

16

24

26

loo 99 3

loo 3

8

12

12

20

22

30

Fenitrothion R

S Malathion

Phoxim

Tetrachlorvinphos

Bromophos

Jodfenphos

S

S

S

25 17.5 10 25 17.5 10

21 0

25 17.5 10

11 1

7 0

100 47

68 53 0

25.5”C against S. granarius. Also using malathion CHADHA et al. (1965) reported a positive correlation against 7: castaneum at 2@25”C and 3&35”C. TEOTIA and PANDEY (1967) confirmed the effect at 27 and 35°C for the same species and using malathion. IORDANEAU and WATTERS (1969) reported positive correlation with both malathion and bromophos at 10, 15.5 and 26.7”C against both T castaneum and 0. surinamensis. More recently O'DONNELL (1980) found positive correlations between temperature and effectiveness of insecticide in Tribolium confusum with malathion, jodfenphos, pirimiphos-methyl and fenitrothion. NORMENT and CHAMBERS (1970) showed similar results with organophosphorus compounds including malathion on the Boll Weevil, Anthonomus grandis (Boheman) and WILKIN and HOWARD (1975) showed three species of storage mites to be less tolerant to pesticides at higher temperature.

S.P.R 18/l-<

P. S. TYLER and T. J. BINNS

2 5 t

T.cost.

::

I Knockdown at 24hr

Key:-

I Mortality offer Sdays

FIG. 1. Relationship between knockdown at 24 hr and kill at 5 days on adults of susceptible strains of three beetle species exposed to chlorpyrifos-methyl at: 10, 50, 100, 500, 1000, 1500, 2000, 3000, 4000 and 5000 mg/m’. 100% mortality always implies 100% knockdown.

2 4

s

T.cost.

P

100

10°C % 0

Key:-

I Knockdown at 24hr

I Mortality

offer Sdays

FIG. 2. Relationship between knockdown at 24 hr and kill at 5 days on adults of susceptible strains of three beetle species exposed to malathion at: 10, 50, 100, 500, 1000, 1500, 2000, 3000, 4000 and 5000 mg/m2. 100% mortality always implies 100% knockdown.

The influence of temperature on insecticides

19

The results obtained in these tests demonstrate that recommended doses should be regarded as temperature specific and some consideration must be given to the decline in effectiveness with lowering of temperature. It may well not prove feasible to compensate for this decline by increasing the dose applied since this could put spray operators at greater risk, lead to residue hazards, or prove uneconomic. Certainly the less effective insecticides should not be used at all where temperatures are very low. In some situations it may be possible to raise the temperature of the treated area sufficiently to activate the insects so that they may pick up a lethal dose. Alternatively, a second compound, having excitant properties might be used in conjunction with the residual insecticides. For example, pyrethrum could be used to drive out insects on to the residual insecticide. The problem assumes particular importance where the control of insecticide-resistant strains is involved. With these it is undesirable to apply a treatment which gives less than a complete kill since by further selection pressure, this level of resistance will be increased. Acknowledgement-The

help of Mr D. F. ROGERS,a student from Brunei University, is gratefully acknowledged. REFERENCES

CHADHA,

D. B.. PERTI,S. L.. DIXIT,R. S. and AGARWAL,P. N. (1965) Effect of temperature and humidity on the susceptibility of insects to insecticides. Abstr., Symp. on Pestic. Mysore, 21-22 December, 1964, 15. (Grain Storage News (1965) I (4). 129, abstr.) CHAMP.B. R. and CAMPBELL-BROWN, M. J. (1970) Insecticide resistance in Australian Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae)- II. Malathion resistance in Eastern Australia. J. stored Prod. Res. 6, 111-131. CHAMP,B. R. and DYTE,C. E. (1976) Report ofthe FAO Global Suroey of Pesticide Susceptibility of Stored Grairl Pests. UN FAO Plant Prod. and Prot. Ser. No. 5. Rome, 297 pp. HOWE, R. W. (1965) A summary of estimates of optimal and minimal conditions for population increase of some stored products insects. J. stored Prod. Res. 1, 177-184. IORDANEAU, N. T. and WATTERS,F. L. (1969) Temperature effects on the toxicity of five insecticides against five species of stored-product insects. J. econ. Ent. 62, 13&135. NORMENT,B. R. and CHAMBERS, H. W. (1970) Temperature relationships in organophosphorus poisoning in boll weevils. J. econ. ht. 63, 5022504. O’DONNELL,M. J. (1980) The toxicities of four insecticides to Tribolium confkum (Duv.) in two sets of conditions of temperature and humidity. J. stored Prod. Res. 16, 71-74. TEOTIA, R. P. S. and PANDEY. K. K. (1967) The influence of temperature and humidity on the contact toxicity of some insecticide deposits on Tribolium castaneum (Herbst). Bull. Grain Technol. 5, 154160. TYLER, P. S. and BINNS, T. J. (1977) The toxicity of seven organophosphorus insecticides and lindane to eighteen species of stored-product beetles. J. stored Prod. Res. 13, 39-43. WILKIN, D. R. and HOWARD,A. (1975) The effect of temperature on the action of four pesticides on three species of storage mites. J. stored Prod. Res. 11, 235-238. ZWICK, R. W. (1962) The effects of aeration protectants, vapour toxicants and cold hardiness to stored grain insects. Ph.D. Thesis, Wash. St. Univ., 1962, 166 pp. University Microfilms, Inc., Ann Arbor, Michigan, 6333035.