DVPLICAT 
 
 m 
 APR 16 19^^ 
 
 Department of Agricultural Investigations 
 American Smelting and Refining Company 
 
 Sterelity in Oats Caused by 
 Grass Thrips 
 
 ^ SvBy 
 Piij(«b'GARA, 
 
 Chief in Charge 
 
 February 1 , 1915 
 
C3^b0« 
 
 0^ 
 
 ^^ 
 
Sterelity in Oats Caused by Grass Thrips 
 
 During the season o£ 1914 our attention was 
 frequently directed to a condition whicti pre- 
 vailed in practically all of the oat fields in the 
 Salt Lake valley, namely, a blighting of the ears 
 or spikelets. About the time that the oat plants 
 were heading it was noted that many of the 
 pikelets were smaller than normal and were 
 whitish and shrivelled. Upon examination it was 
 found that these whitish spikelets had no kernels 
 in them, there being nothing left but the empty 
 husks or glumes; frequently more than fifty per 
 cent of the spikelets were found to be injured 
 and contained no kernels. Invariably, the cause 
 of this condition was not understood by the 
 farmers of the valley. 
 
 A — Head of oats seriously injured by grass 
 thrips (Anaphothrips striatus). Note the small 
 white spikelets in which there are no kernels. 
 
 D — Head of oats in which only a few of the 
 lower spikelets have been injured. Specimens 
 taken in Salt Lake valley by W. W. Jones. (Or- 
 iginal.) 
 
 Popular Name for Injury 
 
 This type of injury to oats has been known 
 for a good many years, and has been frequently 
 referred to as "White-top" and Silver-top" <by 
 reason of the peculiar whitened appearance of 
 the injured spikelets. We have records of injury 
 of this sort from many portions of the United 
 States, Canada and Europe. The cause of the 
 injury is due to a very minute insect known as 
 the grass thrips, Anaphothrips striatus.j This 
 insect is so small and so active in its move- 
 ments that the trained observer will often falT 
 to find it, while the farmer would never see it, 
 even though he were to look for it. This insect 
 averages about one-twentieth of an inch in length 
 and being of a light yellow color is rarely ever 
 noted by the casual observer. 
 
 Life History of the Insect 
 
 The length of the female insect, as stated 
 above, averages about one-twentieth of an inch. 
 The color is yellow, with more or less dusky or 
 brownish shading in some of its parts. Male 
 insects have been found infrequently and, there- 
 fore are much fewer in number than the female. 
 The eggs are bean-shaped and are very minute, 
 being slightly more than one one-hundredth of 
 an inch in length. The adult insects hibernate, 
 that is, live over winter, in places where they 
 have been feeding, such as the slcius of grains 
 which have been cut and have died down, as 
 well as under rubbish and in crevices. They are 
 able to withstand very low temperatures, even 
 as low as fifty-three degrees below zero Fahren- 
 heit. The females become active very early in 
 the spring, at least as soon as the grasses and 
 grains begin to grow. Egg laying soon takes place 
 and may last for a number of weeks, each fe- 
 male being able to deposit from fifty to sixty 
 eggs. In from ten to fifteen days, during the 
 spring months, the eggs are hatched; while dur- 
 ing the summer the time required is from four 
 lo seven days. It requires from twelve to thirty 
 days for the insect to pass from the egg stage 
 to the mature or adult stage. Numerous broods, 
 therefore, appear or are produced, during the 
 summer season, and it has been noted in the 
 Salt Lake valley that this insect is active at 
 least up to the early part of December when-" 
 aver green plants may be found to feed upon. 
 During the past season this insect was noted 
 as being active on volunteer oats as late as De- 
 cemher 12th in localities where the frost had not 
 
U U^l tau ^10 
 
 completely killed the plants. The insect does 
 not confine its attacks to oats, but is found to 
 injure rye, wheat and various grasses. It is a 
 peculiarly injurious insect when it attacks tim- 
 othy. 
 
 Injury Produced 
 In oats the injury is largely confined to the 
 spikelets, although the leaves may also be at- 
 tacked. The injured spikelets are usually more 
 or less whitened or bleached in appearance and 
 are shrivelled and thin. Such spikelets contain 
 no kernels or grains. This injury is largely pro- 
 duced before the spikelets emerge from the 
 sheath or boot. The insects, both young and 
 old, feed mainly within the leaf shea'.hs but 
 may also he found doing Injury outside. The 
 spikelets are attacked before they emerge from 
 the leaf sheaths, both the young and old insects 
 feeding upon them, producing complete sterility 
 by sucking the ovaries and feeding upon other 
 young parts of the flower. It is only when the 
 spikelets emerge from the sheaths that the ex- 
 tent of the injury is noted. As previously stated 
 the injury to oats may reach as high as fifty per 
 cent or more. From what has been noted during 
 the season of 1914 in the Salt Lake valley, it is 
 easy to explain the low yields in most fields. It 
 may be said in passing that the insect which 
 produces such severe Injury to oats belongs to 
 a group or family of insects, many members of 
 which cause great losses to the farmer. As an 
 ■^**^IftnrtSfie, it may be noted that an insect very 
 closely related to the insect described above 
 produces heavy losses to the pear and cherry 
 growers of California. It also attacks other 
 fruits in a serious degree. In California it is 
 known as the most dangerous and destructive in- 
 sect to certain deciduous fruits, and it is one 
 of the hardest to successfully combat. 
 
 Control Measures 
 As the Grass Thrips, which has been noted 
 as seriously attacking oats, feeds on other cer- 
 eals as well as on grasses, it is evident that con- 
 trol would be difficult. Knowing its habits, it 
 is readily seen that grasses, weeds and volun- 
 teer crops of grain should be destroyed in one 
 way or other so as not to provide food and 
 places to hibernate in fields where it is intended 
 to grow oats the following year. It is recom- 
 ^^^ mended that deep fall plowing be practiced, and 
 ^^ Jhis will have its advantages outside of the mat- 
 ter of insect control. It has been suggested also 
 that the stubble be burned after the grain has 
 been cut, but this Is a poor practice from the 
 agricultural point of view. It has been noted 
 that early varieties of oats are less seriously 
 
 injured than the later ripening varieties, and if 
 this proves true, advantage may be taken of 
 them. Where it is desired to put in winter var- 
 ieties of cereals, such as wheat or oats, it has 
 been suggested that either rye or oats be sown 
 in a strip around the field some two or three 
 weeks before planting the winter grain. The in- 
 sects are attracted to such a "trap" crop, and if 
 this crop is removed before the permanent crop 
 appears above the ground, large numbers of the 
 insects will be destroyed. 
 
 In closing it may be said that there is abso- 
 lutely no doubt as to the cause of the injury to 
 oats in the Salt Lake valley, as noted In this 
 paper, or to the identity of the insect. The find- 
 ings of the writer have been fully corroborated 
 by no less an authority than Dr. W. E. Hinds, 
 who for several years was an entomologist in 
 the U. S. Department of Agriculture, and who 
 is now entomologist at the Alabama Agricultural 
 Experiment station. Dr. Hinds made a special 
 study of this group of insects for several years, 
 and is, therefore, our American authority or 
 thrips. 
 
 Illustration of Grass Thrip3 (Anaphothrips stri- 
 atus) Enlarqed About 55 Diameters 
 
 The area covered by the illustration is ap- 
 proximately three thousand times the area that 
 would be covered by the life size specimen. 
 Note the peculiar wings, left being folded and 
 the right extended. 
 (After Fernald and Hinds) 
 
IIIIIIIIIIMIIMIIIIMI 
 
 021 490 275 8 
 
 completely killed the plants. The insect does 
 not confine its attacks to oats, but is found to 
 injure rye, wheat and various grasses. It is a 
 peculiarly injurious insect when it attacks tim- 
 othy. 
 
 Injury Produced 
 In oats the injury is largely confined to the 
 spikelets, although the leaves may also be at- 
 tacked. The injured spikelets are usually more 
 or less whitened or bleached in appearance and 
 are shrivelled and thin. Such spikelets contain 
 no kernels or grains. This injury is largely pro- 
 duced before the spikelets emerge from the 
 sheath or boot. The insects, both young and 
 old, feed mainly within the leaf sheaths but 
 may also be found doing Injury outside. The 
 spikelets are attacked before they emerge from 
 the leaf sheaths, both the young and old insects 
 feeding upon them, producing complete sterility 
 by sucking the ovaries and feeding upon other 
 young parts of the flower. It is only when the 
 spikelets emerge from the sheaths that the ex- 
 tent of the injury is noted. As previously stated 
 the injury to oats may reach as high as fifty per 
 cent or more. From what has been noted during 
 the season of 1914 in the Salt Lake valley, it is 
 easy to explain the low yields in most fields. It 
 may be said in passing that the insect which 
 produces such severe injury to oats belongs to 
 a group or family of insects, many members of 
 which cause great losses to the farmer. As an 
 aJMje, it may be noted that an insect very 
 closely related to the insect described above 
 produces heavy losses to the pear and cherry 
 growers of California. It also attacks other 
 fruits in a serious degree. In California it is 
 known as the most dangerous and destructive in- 
 sect to certain deciduous fruits, and it is one 
 of the hardest to successfully combat. 
 
 Control Measures 
 As the Grass Thrips, which has been noted 
 as seriously attacking oats, feeds on other cer- 
 eals as well as on grasses, it is evident that con- 
 trol would be difficult. Knowing its habits, it 
 is readily seen that grasses, weeds and volun- 
 teer crops of grain should be destroyed in one 
 way or other so as not to provide food and 
 places to hibernate in fields where it is intended 
 to grow oats the following year. It is recom- 
 mended that deep fall plowing be practiced, and 
 ■ Jhis will have its advantages outside of the mat- 
 tei of Insect control. It has been suggested also 
 that the stubble be burned after the grain has 
 been cut, but this is a poor practice from the 
 agricultural point of view. It has been noted 
 that early varieties of oats are less seriously 
 
 injured than the later ripening varieties, and if 
 this proves true, advantage may be taken of 
 them. Where it is desired to put in winter var- 
 ieties of cereals, such as wheat or oats, it has 
 been suggested that either rye or oats be sown 
 in a strip around the field some two or three 
 weeks before planting the winter grain. The in- 
 sects are attracted to such a "trap" crop, and if 
 this crop is removed before the permanent crop 
 appears above the ground, large numbers of the 
 insects will be destroyed. 
 
 In closing it may be said that there is abso- 
 lutely no doubt as to the cause of the injury to 
 oats in the Salt Lake valley, as noted In this 
 paper, or to the identity of the insect. The find- 
 ings of the writer have been fully corroborated 
 by no less an authority than Dr. W. E. Hinds, 
 who for several years was an entomologist in 
 the U. S. Department of Agriculture, and who 
 is now entomologist at the Alabama Agricultural 
 Experiment station. Dr. Hinds made a special 
 study of this group of insects for several years, 
 and is, therefore, our American authority on 
 thrips. 
 
 Illustration of Grass Thrips (Anaphothrips strl- 
 atus) Enlarged About 55 Diameters 
 
 The area covered by the illustration is ap- 
 proximately three thousand times the area that 
 would be covered by the life size specimen. 
 Note the peculiar wings, left being folded and 
 the right extended. 
 (After Fernald and Hinds)