Dwarf phenotype of the cotton aphid, Aphis gossypii glover (Hemiptera: Aphididae)

The cotton aphid, Aphis gossypii Glover, is a polyphagous aphid that is a pest on a wide range of commercially important crops. It sometimes gives birth to small yellow offspring that grow to be only about 1/2 to 1/3 of the typical adult weight. These "yellow dwarfs" differ from the typical form in their small size, by having 5 instead of 6 antennal segments, and by never attaining dark green/black coloration; they are considered to be a separate developmentally-programmed morph. A morphometric description of the yellow dwarf form is provided. Yellow dwarfs develop at a slower rate than typical aphids and have a lower intrinsic rate of increase. An orthogonal experiment demonstrated that production of yellow dwarfs can be induced by presumed less-suitable host-plant species at temperatures of 15° and 25°, but not 20°C. Crowding may also induce birth of yellow dwarfs. Possible advantages of the yellow dwarf developmental pathway are discussed.