SEASONAL ADULT SEX-RATIO SHIFT IN THE PRAYING MANTID IRIS-ORATORIA (MANTODEA, MANTIDAE)

The adult sex ratio of the praying mantid Iris oratoria L. becomes inc reasingly female-biased as the season progresses. This 3-yr field stud y examines 3 possible causes of this shift in sex ratio: differences b etween the sexes in the date of adult eclosion, movement to and from t he census area and adult lifespan. In the field, male and female eclos ion dates did not differ significantly. Movement to and from the censu s area was low for females and males. For each, ear, the number of fem ales that moved into the area (immigrants) exceeded the number that mo ved out ( emigrants), although this difference was not statistically s ignificant in any year. Fewer males were recaptured; those that were d id not show either immigration or emigration. Minimum lifespan for adu lts in the field was greater for females than males. Female lifespan a lso was greater among adults maintained in individual field containers . Furthermore, the eclosion dates of these captive adults did not sign ificantly differ between the sexes, Thus, the sexes evidently eclosed at the same time of year, and the females most likely outlived the mal es in the field. This difference in adult lifespan can lead to an incr easingly female-biased sex ratio over the course of the season, with d ifferent movement patterns between the sexes remaining a possible fact or.