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A technique for marking stored product insects when studying dispersion
J. stored Prod. Res., 1972, Vol. 8, pp. 233-234. Pergamon Press. Printed in Great Britain.
SHORT
A Technique
COMMUNICATION
for Marking Stored Product when Studying Dispersion
(First received 18 May 1972, and inJinalform
20 June
Insects
1972)
NEARLY all dispersal studies involving marked insects have been concerned with pests of growing crops, vectors of disease or honeybees. SOUTHWOOD (1966) describes the various methods of marking insects that have been used. The only work known to the author in which stored product insects were marked for dispersal study is that of GILES (1969), who used paint spotting and radioactive isotope labelling in an attempt to determine the flight range of Sitophilus zeamais Motsch. (Coleoptera, Curculionidae) in Kenya. For a study of the dispersal of S. zeamais infesting maize before harvest in Zambia continuous sources of marked weevils were required. Mass releases of marked weevils in the experimental area were considered inadequate, unnatural and too laborious. This ruled out virtually all the marking techniques employed in other dispersal studies. The principal sources of field infestation of maize by S. zeamais are infested cribs (GILES and ASHMAN, 1971). Such sources are natural and continuous. SMITH and TOWNSEND (1951) adapted beehives so that departing bees were obliged to walk between strips of velveteen liberally dusted with non-toxic fluorescent powder. This technique provided a continuous natural supply of well-marked bees. The technique described here, employing cribs containing maize infested with S. zeamais, is similar in principle but differs in detail. PRELIMINARY
INVESTIGATIONS
S. zeamais adults were placed in jars containing maize grains dusted with fluorescent powders manufactured by Swada (London) Ltd.; Arc chrome, Fire orange and Saturn yellow. No toxic effects were observed, and the maize became heavily infested within a few weeks. Fluorescent powder lodged in cuticular pits on adult weevils emerging from the maize could not be removed easily with either a brush of a jet of water. Weevils bearing traces of fluorescent powder glowed brightly under ultra-violet light in a darkened room, and could be readily distinguished from untreated weevils which have no natural luminescence. The three fluorescent colours could also be easily distinguished from one another under ultra-violet light. FIELD
APPLICATION
Hessian sacks suspended on tripods under individual 233
roofs were used as cribs. Each
234
SHORT
Conihfu~~~rroN
crib contained 50 lb (22.7 kg) of shelled maize uniformly dusted with 2 oz (57 g) of fluorescent powder and infested with about 4000 S. zeamais adults. Prepared cribs were placed 45-100 ft (14-30 m) away from maize plots 8 weeks before observations started. This interval allowed the weevils to settle and produce an F1 generation which would contribute to the number of weevils available for the study period. Records included counts made at regular intervals daily of weevils on crib surfaces and weevils collected from maize plots from the time of 50 per cent cob silking to maturity of the crop. When four cribs were used 66 per cent of 597 weevils collected from the maize plot were found to be marked. In a second study 25 per cent of 714 weevils collected from a circle of maize plants around a single crib had been marked. Checks on the cribs confirmed that weevils could not leave without carrying some fluorescent powder. The high percentage of unmarked weevils found in the maize plots demonstrates the extent of infestation pressure from sources other than those introduced experimentally, and shows the necessity of marking weevils in a situation where it is impossible to exclude wild specimens. In the studies referred to above the nearest sources of ‘wild specimens were maize stores 600 and 100 yd (550 and 92 m) distant respectively. Although the technique was developed for the study of S. zeamais dispersion, it was noted that adults and larvae of Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae) and larvae of Corcyra cephalonica (Staint.), Ephestia cautella (Walker) and Plodia interpuncteUa( Huebn.) (Lepidoptera, Pyralidae) infesting maize in experimental cribs also retained fluorescent powder very well. However, adults of Sitotroga cerealella (Oliv.) (Lepidoptera, Gelechiidae) and the pyralid moths emerging from treated cribs did not carry fluorescent powder. Most of the weevils from treated cribs which were recovered in maize plots were heavily coated with fluorescent powder. Since only a trace of the powder is sufficient to mark a weevil, the application rate of the powder could probably be halved without impairing efficiency. D. L. PROCTOR Tropical Stored Products Centre, ( Tropical Products Institute), Slough, Bucks., England.
REFERENCES GILES, P. H. (1969) Observations in Kenya on the flight activity of stored products insects, particu-
lady Sitopnilus zeamais Motsch. f. stored Prod. Res. 4, 3 17-329. F. (1971) A study of pre-harvest infestation of maize by Sitofihilus uamais Motsch. (Coleoptera, Curculionidae) in the Kenya Highlands. J. stored Prod. Res. 7, 69-83. S~~ITH,M. V. and TOWNSEND,G. l?. (1951) A technique for mass-marking honeybees. Can. Ent. 83, 346-348. SOUTHWOOD, T. R. E. (1966) Ecological methods with particular reference to the study of insect populations. Methuen, London.
GILES, P. H. and ASHMAN,
SHORT
A Technique
COMMUNICATION
for Marking Stored Product when Studying Dispersion
(First received 18 May 1972, and inJinalform
20 June
Insects
1972)
NEARLY all dispersal studies involving marked insects have been concerned with pests of growing crops, vectors of disease or honeybees. SOUTHWOOD (1966) describes the various methods of marking insects that have been used. The only work known to the author in which stored product insects were marked for dispersal study is that of GILES (1969), who used paint spotting and radioactive isotope labelling in an attempt to determine the flight range of Sitophilus zeamais Motsch. (Coleoptera, Curculionidae) in Kenya. For a study of the dispersal of S. zeamais infesting maize before harvest in Zambia continuous sources of marked weevils were required. Mass releases of marked weevils in the experimental area were considered inadequate, unnatural and too laborious. This ruled out virtually all the marking techniques employed in other dispersal studies. The principal sources of field infestation of maize by S. zeamais are infested cribs (GILES and ASHMAN, 1971). Such sources are natural and continuous. SMITH and TOWNSEND (1951) adapted beehives so that departing bees were obliged to walk between strips of velveteen liberally dusted with non-toxic fluorescent powder. This technique provided a continuous natural supply of well-marked bees. The technique described here, employing cribs containing maize infested with S. zeamais, is similar in principle but differs in detail. PRELIMINARY
INVESTIGATIONS
S. zeamais adults were placed in jars containing maize grains dusted with fluorescent powders manufactured by Swada (London) Ltd.; Arc chrome, Fire orange and Saturn yellow. No toxic effects were observed, and the maize became heavily infested within a few weeks. Fluorescent powder lodged in cuticular pits on adult weevils emerging from the maize could not be removed easily with either a brush of a jet of water. Weevils bearing traces of fluorescent powder glowed brightly under ultra-violet light in a darkened room, and could be readily distinguished from untreated weevils which have no natural luminescence. The three fluorescent colours could also be easily distinguished from one another under ultra-violet light. FIELD
APPLICATION
Hessian sacks suspended on tripods under individual 233
roofs were used as cribs. Each
234
SHORT
Conihfu~~~rroN
crib contained 50 lb (22.7 kg) of shelled maize uniformly dusted with 2 oz (57 g) of fluorescent powder and infested with about 4000 S. zeamais adults. Prepared cribs were placed 45-100 ft (14-30 m) away from maize plots 8 weeks before observations started. This interval allowed the weevils to settle and produce an F1 generation which would contribute to the number of weevils available for the study period. Records included counts made at regular intervals daily of weevils on crib surfaces and weevils collected from maize plots from the time of 50 per cent cob silking to maturity of the crop. When four cribs were used 66 per cent of 597 weevils collected from the maize plot were found to be marked. In a second study 25 per cent of 714 weevils collected from a circle of maize plants around a single crib had been marked. Checks on the cribs confirmed that weevils could not leave without carrying some fluorescent powder. The high percentage of unmarked weevils found in the maize plots demonstrates the extent of infestation pressure from sources other than those introduced experimentally, and shows the necessity of marking weevils in a situation where it is impossible to exclude wild specimens. In the studies referred to above the nearest sources of ‘wild specimens were maize stores 600 and 100 yd (550 and 92 m) distant respectively. Although the technique was developed for the study of S. zeamais dispersion, it was noted that adults and larvae of Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae) and larvae of Corcyra cephalonica (Staint.), Ephestia cautella (Walker) and Plodia interpuncteUa( Huebn.) (Lepidoptera, Pyralidae) infesting maize in experimental cribs also retained fluorescent powder very well. However, adults of Sitotroga cerealella (Oliv.) (Lepidoptera, Gelechiidae) and the pyralid moths emerging from treated cribs did not carry fluorescent powder. Most of the weevils from treated cribs which were recovered in maize plots were heavily coated with fluorescent powder. Since only a trace of the powder is sufficient to mark a weevil, the application rate of the powder could probably be halved without impairing efficiency. D. L. PROCTOR Tropical Stored Products Centre, ( Tropical Products Institute), Slough, Bucks., England.
REFERENCES GILES, P. H. (1969) Observations in Kenya on the flight activity of stored products insects, particu-
lady Sitopnilus zeamais Motsch. f. stored Prod. Res. 4, 3 17-329. F. (1971) A study of pre-harvest infestation of maize by Sitofihilus uamais Motsch. (Coleoptera, Curculionidae) in the Kenya Highlands. J. stored Prod. Res. 7, 69-83. S~~ITH,M. V. and TOWNSEND,G. l?. (1951) A technique for mass-marking honeybees. Can. Ent. 83, 346-348. SOUTHWOOD, T. R. E. (1966) Ecological methods with particular reference to the study of insect populations. Methuen, London.
GILES, P. H. and ASHMAN,