54 



in no way specifically related, and that the true position of mdhaleb is 

 where Passerini correctly placed it, in the genus Myzus, whereas 

 humuli, on account of its frontal and antennal characters, belongs to 

 Phorodon. 



LIFE HISTORY OF MYZUS MAHALEB. 



The following account is based mainly upon observations made at 

 Washington, D. 0. : 



The hatching period of the eggs in this latitude ranges from about 

 the 20th of March to the first week in April, being either accelerated 

 or retarded according as the weather is favorable or otherwise, but 

 always at the time when the sap commences to rise and the buds to 

 swell. This period is the most critical in the life history of the species, 

 as numerous individuals will perish from cold and wet if weather 

 changes occur suddenly and frequently, for their ranks may be depleted 

 to such an extent that perhaps not more than 5 or 10 out of 1,000 may 

 succeed in reaching maturity. 



The hatching commences generally about the 15th or 20th of March, 

 so that in a few days, if the weather be favorable, there appear hun- 

 dreds of young larvae on all the twigs and buds. Cold showers and 

 frost, however, during the following days reduce their numbers to such 

 an extent that few can be found. Those which survive attain maturity 

 about the 10th of April — about twenty days or a little more after 

 hatching — and commence at once to deposit their larvae, increasing in 

 number quite rapidly as it becomes warmer and as the leaves expand. 

 Before acquiring full growth the stem-mother casts five skins, changing 

 but little in general appearance, except in size, in the number and 

 length of the antennal joints, and in the length and shape of the nec- 

 taries. The antennae of the mature stem-mother are six-jointed. 



The second generation grows more rapidly than the first, so that 

 many are full-grown before the 25th of April, when they have assumed 

 the general characters of the species, which they retain with but slight 

 alterations through all following generations. The antennae are now 

 seven-jointed and the nectaries long and slender. This generation, as a 

 rule, is apterous, like the preceding generation, though occasionally 

 there develop in one or the other colony one or a few winged individ- 

 uals. These winged specimens are very shy and drop and fly off' at the 

 slightest jar. This early appearance of a few winged specimens is an 

 evident provision of nature to preserve the species from destruction in 

 case a third or genuine migratory generation should fail to reach 

 maturity. The lice now increase quite rapidly in numbers, and station 

 themselves along the midrib of the young leaves, causing them to twist 

 and curl into different shapes. 



The third generation grows still more rapidly, so that many of the 

 oldest individuals are already winged by or before the 5th of May, 

 while the great bulk reached the winged stage between the 9th and 20th 

 of the month. In this generation, as in the preceding, a few individ- 



