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 typicaladult 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 greedblack 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.