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A new technique for sampling experimental grain bulks
J. ,srorcd Prod. Rm. Vol. 19. No. 2. pp. 69-711 1983 Punted in Great Britain. All rights reserved
A NEW TECHNIQUE
0022-474X/83/020069-03$03.00/0 Copyright mi:’1983 Pergamon Press Ltd
FOR SAMPLING GRAIN BULKS
EXPERIMENTAL
B. C. LONGSTAFF and J. POCKNALL CSIRO Divisionof Entomology,P.O. Box 1700, Canberra City,
A.C.T.
2601, Australia
(Received in final form 29 November 1982) Abstract-A sampling technique is described which minimises the habitat disturbance that occurs during frequent sampling of a small grain bulk. The technique permits the replacement of sampled grain and insects at the original site of sampling, thereby preventing grain from collapsing into the space left by sample extraction.
INTRODUCTION In experimental studies of the dispersal of grain-infesting insects within a mass of grain it is necessary to take samples periodically to assess both population density and distribution. Small, localized infestations may give rise to “hot-spots”, areas where, owing to the poor thermal conductivity of grain, heat produced by the metabolic activities of the insects causes marked temperature rises. The removal of a sample of grain from such a “hot-spot”, by means of the normal suction spear (Burges, 1960), brings about a funnelling of the surrounding grain into the space left by the sample (Howe, 1965; Howe and King, 1964). Thus it is likely that a “hot-spot” may be broken up, and the pattern of distribution of the insect population altered. Furthermore, the sampled grain and any insects therein are usually either destroyed or returned to the top of the grain bulk, further altering the distribution of the pests. Whilst such disturbances are unlikely to be of importance in commercial storages, they could well have some effect in smaller, experimental systems. In current studies of the relationship between the dispersal of the rice weevil, Sitophilus oryzae (L.), and temperature and moisture content gradients within a 5-t bulk of wheat, the sampling program requires that forty samples be taken each week, for 1 year, from each experimental silo. Because each sample must be of at least 100 g to permit the estimation of grain moisture content by a rapid, non-destructive method, appreciable redistribution of grain and insects would occur if the sampled grain were simply returned to the surface of the grain bulk. To overcome these problems a sampling spear was constructed that permitted the sampled grain and insects to be returned to the original location within the grain bulk with the minimum of disturbance.
DESCRIPTION
OF APPARATUS
The basic form of the spear is shown in Fig. la. It consists of a sampling chamber which is inserted into the grain and from which the grain sample can be removed by suction and replaced by gravity feed. The sampling chamber at the end of the spear is in 2 parts (Fig. lb). The outer part is a hollow cylinder capped with a cone and fixed at the top to an outer tube. The solid inner part is shaped to occupy half the outer part and keyed to an inner tube which rotates against the outer part about a bearing at the top of the chamber (Fig. lb). Rotation of the inner part permits either entry of grain for sampling or complete removal of the sample from the outer chamber so that it may be left in its original position as the spear is extracted. At the top of the spear, the inner tube is attached to a knurled grip to rotate the inner half of the sampling chamber, when collecting or expelling samples. Two levers (Fig. la) on the side of this grip control upward and downward movement of the grip/inner tube assembly necessary for complete removal of sample (Fig. Ic). The bottom section of the inner tube is tapered to a semi-circular section, to allow it to move over the flat surface of the inner part of the head. 69
B. C. LONGSTAFF and J. POCKNALL
Solid inner
Fig. I. (a) Sampling spear held in alignment protractor structure of the sampling spear. (c) The position
on top of grain silo. (b) Details of the internal of the inner tube after sample removal.
PROCEDURE The sampling procedure is as follows. The spear is located in an alignment protractor, which is positioned over the opening at the top of silo. The protractor allows the accurate placement of the sampling chamber at defined points within the grain bulk. The markings on the protractor correspond with markings on the shaft of the spear and represent particular points within the grain bulk. Once in the alignment protractor, the spear is inserted into the grain, with the sampling chamber closed. When the required position is reached, a sample is taken by opening and closing the chamber. This sample is then extracted by suction and is collected in a jar, after deceleration in a cyclone separator to minimise grain and insect damage. Suction is generated by a vacuum cleaner and it takes between 6 and 8 set to collect the sample. In a test run the rate of air flow through the sampler head measured by means of a rotameter, proved to be about 60 l/set and did not vary significantly with depth in the 2 m deep bulk. To ensure that all of the sample is removed from the sampling chamber, the inner tube is gradually lowered into the chamber as the suction is applied (Fig. lc). This is achieved by squeezing the two levers on the knurled grip (Fig. la) which disengage from the outer tube, allowing the grip and inner tube to move down. Once the sample has been collected the tube is withdrawn from the chamber. The moisture content of the grain may then be determined with a Cera-tester. The number of adult weevils present in the sample is determined and the grain and insects returned to the sampling chamber, via the funnel at the top
A new grain
sampling
71
technique
of the spear. The chamber is then opened and the spear withdrawn, leaving the sample behind in approximately the position from whence it came. The spear is then reinserted at a new position. DISCUSSION To assess whether or not the objective of returning the grain sample to its point of extraction had been achieved, grains that had been stained bright green were returned to a mass of normal grain. The grain was then removed from the top until coloured grains were found, and, with the exception of one or two isolated grains, the sample was found to be where expected. This technique, therefore, minimizes the disturbance to the grain bulk by preventing any significant displacement of grain during sampling. Acknowledgements-The authors would like to thank and Graham K. Smith for drawing the illustrations.
Graham
P. Smith for his assistance
in the development
of this device
REFERENCES Burges H. (1960) A spear for sampling bulk grain by suction. Bull en?. Res. 51, l-5. Howe R. W. (1965) Investigation of the efficiency of spear sampling of bulk grain. Proc. XZZ Znf. Congr. En?., London, 1964. p. 629. Howe R. W. and King R. K. (1964) Problems of sampling for insects in bulks of grain. Pest Infest. Res. 1963, p. 46. Agric. Res. Council, London.
A NEW TECHNIQUE
0022-474X/83/020069-03$03.00/0 Copyright mi:’1983 Pergamon Press Ltd
FOR SAMPLING GRAIN BULKS
EXPERIMENTAL
B. C. LONGSTAFF and J. POCKNALL CSIRO Divisionof Entomology,P.O. Box 1700, Canberra City,
A.C.T.
2601, Australia
(Received in final form 29 November 1982) Abstract-A sampling technique is described which minimises the habitat disturbance that occurs during frequent sampling of a small grain bulk. The technique permits the replacement of sampled grain and insects at the original site of sampling, thereby preventing grain from collapsing into the space left by sample extraction.
INTRODUCTION In experimental studies of the dispersal of grain-infesting insects within a mass of grain it is necessary to take samples periodically to assess both population density and distribution. Small, localized infestations may give rise to “hot-spots”, areas where, owing to the poor thermal conductivity of grain, heat produced by the metabolic activities of the insects causes marked temperature rises. The removal of a sample of grain from such a “hot-spot”, by means of the normal suction spear (Burges, 1960), brings about a funnelling of the surrounding grain into the space left by the sample (Howe, 1965; Howe and King, 1964). Thus it is likely that a “hot-spot” may be broken up, and the pattern of distribution of the insect population altered. Furthermore, the sampled grain and any insects therein are usually either destroyed or returned to the top of the grain bulk, further altering the distribution of the pests. Whilst such disturbances are unlikely to be of importance in commercial storages, they could well have some effect in smaller, experimental systems. In current studies of the relationship between the dispersal of the rice weevil, Sitophilus oryzae (L.), and temperature and moisture content gradients within a 5-t bulk of wheat, the sampling program requires that forty samples be taken each week, for 1 year, from each experimental silo. Because each sample must be of at least 100 g to permit the estimation of grain moisture content by a rapid, non-destructive method, appreciable redistribution of grain and insects would occur if the sampled grain were simply returned to the surface of the grain bulk. To overcome these problems a sampling spear was constructed that permitted the sampled grain and insects to be returned to the original location within the grain bulk with the minimum of disturbance.
DESCRIPTION
OF APPARATUS
The basic form of the spear is shown in Fig. la. It consists of a sampling chamber which is inserted into the grain and from which the grain sample can be removed by suction and replaced by gravity feed. The sampling chamber at the end of the spear is in 2 parts (Fig. lb). The outer part is a hollow cylinder capped with a cone and fixed at the top to an outer tube. The solid inner part is shaped to occupy half the outer part and keyed to an inner tube which rotates against the outer part about a bearing at the top of the chamber (Fig. lb). Rotation of the inner part permits either entry of grain for sampling or complete removal of the sample from the outer chamber so that it may be left in its original position as the spear is extracted. At the top of the spear, the inner tube is attached to a knurled grip to rotate the inner half of the sampling chamber, when collecting or expelling samples. Two levers (Fig. la) on the side of this grip control upward and downward movement of the grip/inner tube assembly necessary for complete removal of sample (Fig. Ic). The bottom section of the inner tube is tapered to a semi-circular section, to allow it to move over the flat surface of the inner part of the head. 69
B. C. LONGSTAFF and J. POCKNALL
Solid inner
Fig. I. (a) Sampling spear held in alignment protractor structure of the sampling spear. (c) The position
on top of grain silo. (b) Details of the internal of the inner tube after sample removal.
PROCEDURE The sampling procedure is as follows. The spear is located in an alignment protractor, which is positioned over the opening at the top of silo. The protractor allows the accurate placement of the sampling chamber at defined points within the grain bulk. The markings on the protractor correspond with markings on the shaft of the spear and represent particular points within the grain bulk. Once in the alignment protractor, the spear is inserted into the grain, with the sampling chamber closed. When the required position is reached, a sample is taken by opening and closing the chamber. This sample is then extracted by suction and is collected in a jar, after deceleration in a cyclone separator to minimise grain and insect damage. Suction is generated by a vacuum cleaner and it takes between 6 and 8 set to collect the sample. In a test run the rate of air flow through the sampler head measured by means of a rotameter, proved to be about 60 l/set and did not vary significantly with depth in the 2 m deep bulk. To ensure that all of the sample is removed from the sampling chamber, the inner tube is gradually lowered into the chamber as the suction is applied (Fig. lc). This is achieved by squeezing the two levers on the knurled grip (Fig. la) which disengage from the outer tube, allowing the grip and inner tube to move down. Once the sample has been collected the tube is withdrawn from the chamber. The moisture content of the grain may then be determined with a Cera-tester. The number of adult weevils present in the sample is determined and the grain and insects returned to the sampling chamber, via the funnel at the top
A new grain
sampling
71
technique
of the spear. The chamber is then opened and the spear withdrawn, leaving the sample behind in approximately the position from whence it came. The spear is then reinserted at a new position. DISCUSSION To assess whether or not the objective of returning the grain sample to its point of extraction had been achieved, grains that had been stained bright green were returned to a mass of normal grain. The grain was then removed from the top until coloured grains were found, and, with the exception of one or two isolated grains, the sample was found to be where expected. This technique, therefore, minimizes the disturbance to the grain bulk by preventing any significant displacement of grain during sampling. Acknowledgements-The authors would like to thank and Graham K. Smith for drawing the illustrations.
Graham
P. Smith for his assistance
in the development
of this device
REFERENCES Burges H. (1960) A spear for sampling bulk grain by suction. Bull en?. Res. 51, l-5. Howe R. W. (1965) Investigation of the efficiency of spear sampling of bulk grain. Proc. XZZ Znf. Congr. En?., London, 1964. p. 629. Howe R. W. and King R. K. (1964) Problems of sampling for insects in bulks of grain. Pest Infest. Res. 1963, p. 46. Agric. Res. Council, London.