. Bulletin of the Department of Agriculture. Agriculture; Agriculture -- United States. Fig. 20.—Ripe grapefmit showing copious gummy secretions that may, though more often do not, follow attack by Mediterranean fruit fly. (Original.) that tliey fall to the ground. Why, then, are Chinese oranges and tangerines easily infested with larvae in the pulp whereas lemons, grapefruit, and oranges ward off fatal attack either entirely or until after they are overripe ? The reason is that a great mortahty oc- curs among the eggs and newly hatched larvae in citrus fruits having a thick peel- ing or
. Bulletin of the Department of Agriculture. Agriculture; Agriculture -- United States. Fig. 20.—Ripe grapefmit showing copious gummy secretions that may, though more often do not, follow attack by Mediterranean fruit fly. (Original.) that tliey fall to the ground. Why, then, are Chinese oranges and tangerines easily infested with larvae in the pulp whereas lemons, grapefruit, and oranges ward off fatal attack either entirely or until after they are overripe ? The reason is that a great mortahty oc- curs among the eggs and newly hatched larvae in citrus fruits having a thick peel- ing or rind. In Chi- nese oranges the peel is so thin that the fruit fly can lay her eggs through it into the pulp itself or between the pulp and the rind, so that the larvae on hatching can at once begin to feed on the pulp. As a result the pulp of the Cliinese orange (fig. 18) is almost always infested with larvfe. The case is different vdih lemons (fig. 19), grapefruit (fig. 20), and ordi- nary seedling oranges. In these fruits the peel is so thick that the fly must deposit her eggs in the outer part of tlie white rag as illustrated in figure 21. In making the punctm'e she often ruptures an oil ceU in the rind, and the oil thus liberated kiUs the eggs. But if the eggs are laid between oil cells, the young larvae have difficulty in making their way through the rag to the pulp, and a very high percentage of them die in the attempt. Then, too, a gaU-like hardening develops quite rapidly about the egg cavity in oranges, grape- fruit, and lemons, as indicated by the darkened area about the egg cavity in figm'e 21. This hardening often makes of the cavity a prison from which the young larvae can not escape and in which they are literally starved to death. It thus happens that the larvae that succeed in entering the rag of the peel from the egg cavity are able to reach the pulp of grapefruit. Fig. 21.—Section of grapefruit rind, showing two egg cavi- ties, one in cross section. Drawin
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectagriculture, bookyear
