- Email: [email protected]
A noninclusion virus of blow-fly larvae
JOURNAL
OF INVERTEBRATE
PATHOLOGY
13, 310-311
A Noninclusion
(1969)
Virus
Larvae of certain blowflies, typically Calliphora and Phormia spp., are reared in large numbers each year as bait for fishermen. During the mid-summer of 1967 and 1968 a significant number of larvae which were being reared in large out-door pits were observed to be dying. The larvae were being fed on mixed offal (including a certain amount of fish) on a continuous basis; that is to say, young maggots and more food were added to the pits until they were full of waste. The pits were very foul; these conditions might be regarded as likely to favor the development and spread of disease. However, the method had been used in several previous years without mishap and when dead larvae were seen, it was only after insecticides and disinfectants on the offal had been eliminated as the cause of death that disease was considered. The affected larvae were usually in the middle period of their development. They were sluggish in movement and most easily seen when stranded on the drying surface of the beds of offal. In general appearance they were rather white and opaque in comparison with healthy larvae which were more translucent, The affected larvae were also less smoothly round but it is uncertain to what extent these differences were the direct or secondary results of the disease. When larvae which had recently died were examined with the light microscope no parasites were found and abnormal numbers of bacteria were not present. Some of the larvae were then crushed individually
310
of Blow-Fly
Larvae
in small drops of water and a little of the fluid was examined with the electron microscope using 1% solutions of phosphotungstic acid and uranyl acetate as negative stains. In four out of five of these preparations varying numbers of apparently round particles with mean diameter of 2.35 A ( f 5% ) were observed. (Fig. la and b). Some of these particles appeared to be “empty” ( top component), but most were apparently “full,” and closer examination of the prints suggested that both were, in fact, icosahedral in shape. No such particles were found in six healthy larvae, and it seems reasonable to conclude that the particles are a small virus resembling those previously found in certain Hymenoptera by L. Bailey, A. J. Gibbs, and R. D. Woods (Virology, 23, 425429, 1964) and Lepidoptera by K. A. Harrap, J. F. Longworth, T .W. Tinsley, and K. W. Brown (J. Invertebrate Pathol., 8, 270-272, 1966) but not, so far, reported in muscoid Diptera. ACKNOWLEDGMENT
The author thanks partment of Zoology advice and assistance
Dr. A. W. Grimstone, Deof this University for kind with the electron micros-
copy. W.
A. L.
Glasshouse Crops Research Znstitute Insect Virus Group (Cambridge ) University Farm Road Cambridge, England Received
December
18, 1968
DAVID
FIGS. la and b. Viruslike particles from moribund and dead blow-fly larvae stained (a) with phosphotungstic acid (b) with uranyl acetate. Some apparently “empty” particles and particles with angular outlines can be seen. 350,000 X. 311
OF INVERTEBRATE
PATHOLOGY
13, 310-311
A Noninclusion
(1969)
Virus
Larvae of certain blowflies, typically Calliphora and Phormia spp., are reared in large numbers each year as bait for fishermen. During the mid-summer of 1967 and 1968 a significant number of larvae which were being reared in large out-door pits were observed to be dying. The larvae were being fed on mixed offal (including a certain amount of fish) on a continuous basis; that is to say, young maggots and more food were added to the pits until they were full of waste. The pits were very foul; these conditions might be regarded as likely to favor the development and spread of disease. However, the method had been used in several previous years without mishap and when dead larvae were seen, it was only after insecticides and disinfectants on the offal had been eliminated as the cause of death that disease was considered. The affected larvae were usually in the middle period of their development. They were sluggish in movement and most easily seen when stranded on the drying surface of the beds of offal. In general appearance they were rather white and opaque in comparison with healthy larvae which were more translucent, The affected larvae were also less smoothly round but it is uncertain to what extent these differences were the direct or secondary results of the disease. When larvae which had recently died were examined with the light microscope no parasites were found and abnormal numbers of bacteria were not present. Some of the larvae were then crushed individually
310
of Blow-Fly
Larvae
in small drops of water and a little of the fluid was examined with the electron microscope using 1% solutions of phosphotungstic acid and uranyl acetate as negative stains. In four out of five of these preparations varying numbers of apparently round particles with mean diameter of 2.35 A ( f 5% ) were observed. (Fig. la and b). Some of these particles appeared to be “empty” ( top component), but most were apparently “full,” and closer examination of the prints suggested that both were, in fact, icosahedral in shape. No such particles were found in six healthy larvae, and it seems reasonable to conclude that the particles are a small virus resembling those previously found in certain Hymenoptera by L. Bailey, A. J. Gibbs, and R. D. Woods (Virology, 23, 425429, 1964) and Lepidoptera by K. A. Harrap, J. F. Longworth, T .W. Tinsley, and K. W. Brown (J. Invertebrate Pathol., 8, 270-272, 1966) but not, so far, reported in muscoid Diptera. ACKNOWLEDGMENT
The author thanks partment of Zoology advice and assistance
Dr. A. W. Grimstone, Deof this University for kind with the electron micros-
copy. W.
A. L.
Glasshouse Crops Research Znstitute Insect Virus Group (Cambridge ) University Farm Road Cambridge, England Received
December
18, 1968
DAVID
FIGS. la and b. Viruslike particles from moribund and dead blow-fly larvae stained (a) with phosphotungstic acid (b) with uranyl acetate. Some apparently “empty” particles and particles with angular outlines can be seen. 350,000 X. 311