. Bulletin of the Department of Agriculture. Agriculture. 20 BULLETIN 918, U. S. DEPARTMENT OF AGEICULTUEE. cotton plants during March and April, 1918, were unsuccessful. The first eggs were laid in the breeding jars on May 5, and the first larva (one of the third instar) was foimd in cotton in the field on May 15, 1918. The first eggs were deposited on April 9, 1919, and the first larva found in the field on April 28. The general infestation in the fields, however, did not begin till later in 1919 than in 1918. In general, it may be said that breeding commences in the spring as soon as t
. Bulletin of the Department of Agriculture. Agriculture. 20 BULLETIN 918, U. S. DEPARTMENT OF AGEICULTUEE. cotton plants during March and April, 1918, were unsuccessful. The first eggs were laid in the breeding jars on May 5, and the first larva (one of the third instar) was foimd in cotton in the field on May 15, 1918. The first eggs were deposited on April 9, 1919, and the first larva found in the field on April 28. The general infestation in the fields, however, did not begin till later in 1919 than in 1918. In general, it may be said that breeding commences in the spring as soon as the squares begin to mature and by the time the first blossoms appear a few larvae are present. The infestation is extremely light at this season and only by careful search will any larvae be fomid. As a rule the bolls are not attacked till they are from one-half to three-fourths grown, though occasionally a larva works down from the blossom to the newly set boll. It is usually about the middle to latter part of July before boUs on plant cotton are sufficiently mature to be attractive to the larvae. From this date onward the infestation rapidly increases, and in about 10 weeks' time practically every green boll is infested. The cool nights of October and November check the development somewhat, but breeding continues until frost destroys the food plants. Table IX shows the weekly increase in the percentage of green bolls infested during the 10 weeks during which breeding is most active. It is computed from weekly examinations of samples of green bolls collected on different plantations, an average number of 350 in 1918 and 1,100 in 1919 being used. Table IX.— The weekly increase in the percentage of green bolls infested with Pectino- phora gossypiella. Week ending- July July 19., July Aug. Aug. Aug. 16. Aug. 23. Percentage of green bolls infested. 1918. 1919. 1 Sept. 27 Oct. 4 Oct. 11 Percentage of green bolls i
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