- Email: [email protected]
Susceptibility of two strains of Indian meal moth to a granulosis virus
JOURNAL
OF INVERTEBRATE
21, 114-115
PATHOLOGY
Susceptibility
(1973)
of Two Strains Granulosis
This report describes a difference in susceptibility to granulosis virus exhibited by two strains of the Indian meal moth, Plodia interpunctella. “Strain A” was obtained in 1961 from an old laboratory colony in Savannah, Georgia; it has since been maintained in the Fresno laboratory. Insects from “Strain A” were used in a previously report’ed study on the pathogenicity of the granulosis virus (D. I<. Hunter, J. Invertebr. Pathol. 16, 339-341, 1970). “Strain B” was colonized in 1969 with larvae collected at Modesto, California, and has been observed to be ex-
7-
> 6Ii 2 5: 5 4Im 0 a 3P A. 1;,.~~2+,.026(~-3.92,)
2.
B. ~:~.~62+,.,*,(~-4.835)
i
i
LOG
i
k
1
8
6
7
CONCENTRATION
FIG. 1. Concentration-mortality curves from two strains of Plodin infe,punctella exposed to a granulosis virus. Equations describing the curves are given. “A” represents an older, less vigorous culture, and “B” a younger, more vigorous culture. The broken line represents “A” from an earlier study.
of Indian Virus
@ 1973
by Academic
Press,
Inc.
Moth
to a
tremely vigorous. Adults of a generation emerge 3-4 days earlier (at 27OC), lay more fertile eggs, and appear larger in size than those of “Strain A.” Initially, both laboratory strains had occasional outbreaks of granulosis virus. The potential disease problem was controlled by surface-sterilizing eggs with 4% formaldehyde, and by retaining only the most vigorous individuals of each generation for breeding stock. Preliminary pathogenicity tests using “Strain B” gave conflicting results when mortality percentages at particular virus concentrations were compared with those from “Strain A.” The data indicated that higher concentrations of virus were required to kill larvae of ‘Strain B.” Therefore, a comparative assay was conducted to determine whether different levels of susceptibility to granulosis virus occurred. First-instar larvae were exposed to purified virus on bran diet in 8-0~ cartons. The inoculum used in the study reported here as well as in the above-mentioned study was prepared from cadavers obtained from Tifton, Georgia. Concentrations of 1.8 x lo?, 1.8 X 103, 1.8 X lo”, and 1.8 X lo5 capsules per gram were tested against “Strain A,” while concent,rations of 1.8 x 103, 1.8 X lOa, 1.8 X lo”, and 1.8 X 10fiwere tested against “Strain B.” The larvae were incubated at 27%, and the resultant mortalities were based on adult emergence. All mortality percentages were corrected by Abbott’s formula (W. S. Abbott, J. Econ. Entomol. 18, 265-267, 1925.). Table 1 shows the mortalities resulting
114 Copyright
Meal
NOTES TABLE LARVAL
MORTALITY Two
115 1
BY ADULT EMERGENCIC) FROM PERORAL EXPOSURJZ MF:TAL MOTH TO h GRANULOSIS VIRUS
(as DETERMINED STRNNS OF INDIAN
Adult No. larvae/ trial
Capsules/g 1.8 1.8 1.8 1.8 1.8
x x x x x CK
106 106 10” 103 lo2
75 75 75 75 75 75
Strain Trial
1
A (Georgia) Trial
-
-
3 36 59 70 73
4 31 56 54 68
2
emergence
Strain Trial 2 38 65 67 69
from peroral exposure to various dosages of virus in three trials. Figure 1 shows probit mortality plotted against log concentration. Mortality curves are shown for the original study with “Strain A” (Hunter, lot. cit.), and the curves were calculated for both strains in the study reported here. Equations describing the latter two curves are also given. The calculated LC,, for YStrain A” in the study reported here was 12,300 capsules per gram of diet with fiducial limits (0.05) lying at 12,150 and 12,500 capsules per gram. The LC,, for strain B was 89,550 capsules per gram with fiducial limits at 88,300 and 90,800 capsules per gram. Based on these values, greater than a 7-fold difference in susceptibility
3
Trial 5 41 59 71 74
OF
B (California) 1
Trial 0 22 59 66 74
2
Avg.
Trial
3
0 24 60 74 74
% mortality A
B
95 49 13 8
07 60 19 4 -
exists between the two strains of Indian meal moths. The difference in susceptibility of the strains may be due to genetic differences that were present in the wild populations from which the insects were originally collected or from differences that occurred in the strains as a result of length of time under colonization. D. K. HUNTER D. F. HOFFMANN Stored-Product Insects Research Laboratory 5578 Air Terminal Drive Fresno, California 93727 Received June 29, 1972
OF INVERTEBRATE
21, 114-115
PATHOLOGY
Susceptibility
(1973)
of Two Strains Granulosis
This report describes a difference in susceptibility to granulosis virus exhibited by two strains of the Indian meal moth, Plodia interpunctella. “Strain A” was obtained in 1961 from an old laboratory colony in Savannah, Georgia; it has since been maintained in the Fresno laboratory. Insects from “Strain A” were used in a previously report’ed study on the pathogenicity of the granulosis virus (D. I<. Hunter, J. Invertebr. Pathol. 16, 339-341, 1970). “Strain B” was colonized in 1969 with larvae collected at Modesto, California, and has been observed to be ex-
7-
> 6Ii 2 5: 5 4Im 0 a 3P A. 1;,.~~2+,.026(~-3.92,)
2.
B. ~:~.~62+,.,*,(~-4.835)
i
i
LOG
i
k
1
8
6
7
CONCENTRATION
FIG. 1. Concentration-mortality curves from two strains of Plodin infe,punctella exposed to a granulosis virus. Equations describing the curves are given. “A” represents an older, less vigorous culture, and “B” a younger, more vigorous culture. The broken line represents “A” from an earlier study.
of Indian Virus
@ 1973
by Academic
Press,
Inc.
Moth
to a
tremely vigorous. Adults of a generation emerge 3-4 days earlier (at 27OC), lay more fertile eggs, and appear larger in size than those of “Strain A.” Initially, both laboratory strains had occasional outbreaks of granulosis virus. The potential disease problem was controlled by surface-sterilizing eggs with 4% formaldehyde, and by retaining only the most vigorous individuals of each generation for breeding stock. Preliminary pathogenicity tests using “Strain B” gave conflicting results when mortality percentages at particular virus concentrations were compared with those from “Strain A.” The data indicated that higher concentrations of virus were required to kill larvae of ‘Strain B.” Therefore, a comparative assay was conducted to determine whether different levels of susceptibility to granulosis virus occurred. First-instar larvae were exposed to purified virus on bran diet in 8-0~ cartons. The inoculum used in the study reported here as well as in the above-mentioned study was prepared from cadavers obtained from Tifton, Georgia. Concentrations of 1.8 x lo?, 1.8 X 103, 1.8 X lo”, and 1.8 X lo5 capsules per gram were tested against “Strain A,” while concent,rations of 1.8 x 103, 1.8 X lOa, 1.8 X lo”, and 1.8 X 10fiwere tested against “Strain B.” The larvae were incubated at 27%, and the resultant mortalities were based on adult emergence. All mortality percentages were corrected by Abbott’s formula (W. S. Abbott, J. Econ. Entomol. 18, 265-267, 1925.). Table 1 shows the mortalities resulting
114 Copyright
Meal
NOTES TABLE LARVAL
MORTALITY Two
115 1
BY ADULT EMERGENCIC) FROM PERORAL EXPOSURJZ MF:TAL MOTH TO h GRANULOSIS VIRUS
(as DETERMINED STRNNS OF INDIAN
Adult No. larvae/ trial
Capsules/g 1.8 1.8 1.8 1.8 1.8
x x x x x CK
106 106 10” 103 lo2
75 75 75 75 75 75
Strain Trial
1
A (Georgia) Trial
-
-
3 36 59 70 73
4 31 56 54 68
2
emergence
Strain Trial 2 38 65 67 69
from peroral exposure to various dosages of virus in three trials. Figure 1 shows probit mortality plotted against log concentration. Mortality curves are shown for the original study with “Strain A” (Hunter, lot. cit.), and the curves were calculated for both strains in the study reported here. Equations describing the latter two curves are also given. The calculated LC,, for YStrain A” in the study reported here was 12,300 capsules per gram of diet with fiducial limits (0.05) lying at 12,150 and 12,500 capsules per gram. The LC,, for strain B was 89,550 capsules per gram with fiducial limits at 88,300 and 90,800 capsules per gram. Based on these values, greater than a 7-fold difference in susceptibility
3
Trial 5 41 59 71 74
OF
B (California) 1
Trial 0 22 59 66 74
2
Avg.
Trial
3
0 24 60 74 74
% mortality A
B
95 49 13 8
07 60 19 4 -
exists between the two strains of Indian meal moths. The difference in susceptibility of the strains may be due to genetic differences that were present in the wild populations from which the insects were originally collected or from differences that occurred in the strains as a result of length of time under colonization. D. K. HUNTER D. F. HOFFMANN Stored-Product Insects Research Laboratory 5578 Air Terminal Drive Fresno, California 93727 Received June 29, 1972