Hc. Rowe et Cm. Bristow, Sex ratio and sexual dimorphism in Formica exsectoides, the Allegheny mound ant (Hymenoptera : Formicidae), GT LAKE ENT, 32(3), 1999, pp. 207-218
We excavated 66 mounds from 6 populations of Formica exsectoides in Michiga
n jack pine, collecting sexual caste pupae for sex ratio estimates and meas
urement of dimorphism. Reproductive caste brood was present in only 37 of t
he 66 mounds, and presence of reproductive caste brood was associated with
larger mound surface area. Females were heavier than males, but did not dif
fer from males in energy density. Sexes did not differ in timing or rate of
development. Sex ratio estimates based on individual mounds ranged from 1.
0 (all male) to 0.08 (female-biased). Four of the six study populations wer
e strongly male-biased, while sex ratio estimates for the remaining populat
ions did not; differ from equal investment. While this interpopulation vari
ation may be caused by genetic factors, the equal investment populations we
re located in or near patches of clear-cut forest, suggesting that environm
ental impacts should be investigated.