Supplemental Table S1: Estimates of sexual isolation in the laboratory between I. denticollis and I. gemina, and sexual-mechanical isolation in the field between I. damula and I. demorsa in samplings that took place between 1962 to 1967 from14 sympatric localities in south-western New Mexico. It is shown the number of conspecific and heterospecific attempts to tandem or matings observed and expected (under random mating). First and second columns explain the generation and the type of crossing: DEN: I. denticollis, GE: I. gemina, DA: I. damula and DEM: I. demorsa.

Generation / Cross / Observed / Expected / Source
First: Parental species / ♂DEN♀DEN / 84 / 69.5 / Tierney 1994
♂GE♀GE / 76 / 53.5 / Tierney 1994
♂DA♀DA / 102 / 60 / Johnson 1975
♂DEM♀DEM / 123 / 70 / Johnson 1975
Second: F1-hybrids / ♂DEN♀GE / 55 / 69.5 / Tierney 1994
♂GE♀DEN / 31 / 53.5 / Tierney 1994
♂DEM ♀DA / 18 / 70 / Johnson 1975
♂DA♀DEM / 17 / 60 / Johnson 1975

Supplemental Table S2: Estimates of mechanical isolationI and II. First and second columns explain the generation and the type of crossing: DEN: I. denticollis and GE: I. gemina. Columns of attempts to tandem, tandem and matings represent the absolute number of the observed sexual activity.

Generation / Cross / MechanicalI
(tandem/attempt to tandem) / MechanicalII
(copula /tandem) / Source
First: Parental species / ♂DEN♀DEN / 44.04% (37/84) / 47.76% (32/67) / Tierney 1994
♂GE♀GE / 68.42% (51/76) / 54.31% (63/116) / Tierney 1994
♂DEN♀GE / 0.31% (3/971) / 33.33% (1/3) / Tierney 1994
♂GE♀DEN / 10.41% (76/730) / 11.68% (9/77) / Tierney 1994

Supplemental Table S3: Estimates of oviposition success, fertility and fecundity, survivorship and sex ratio of conspecific and heterospecific crosses. First and second columns represent the type of crossing. DEN: I. denticollis, GE: I. gemina, DA: I. damula, DEM: I. demorsa and H: hybrids. Sample size (N) indicates the number of females, SE denotes standard error. “na” denotes cases were data are not available.

Generation / Cross / N / Oviposition / Fecundity / Fertility / Survivorship / Sex-ratio / Source
First: Parental species / ♂DEN♀DEN / 5 / 100% / na / 0.83 / 11.00 / 0.44 / Tierney 1994
♂GE♀GE / 2 / 100% / 302.75±22.75 / 0.96±0.02 / 18.00 / 0.53 / Tierney 1994
♂DA♀DA / 4 / 100% / 129.29±5.61 / 0.70±0.00 / na / na / Johnson 1975
♂DEM♀DEM / 2 / 100% / 139.29±3.57 / 0.70±0.00 / na / na / Johnson 1975
Second: F1-hybrids / ♂DEN♀GE / 1 / 100% / 92.50 / 0.67 / 0.00 / -- / Tierney 1994
♂GE♀DEN / 9 / 100% / 190.83±20.89 / 0.95±0.02 / 7.00 / 0.48 / Tierney 1994
♂DEM ♀DA / 10 / 60% / 56.67±9.82 / 43.38±2.85 / 0.00 / -- / Johnson 1975
♂DA♀DEM / 8 / 50% / 35.75±2.78 / 29.95±6.37 / 0.00 / -- / Johnson 1975
Third: F2 -hybrids / ♂DEN♀H / 2 / 100% / 46.00±34.50 / 0.90±0.03 / na / na / Tierney 1994
♂H♀DEN / 2 / 100% / 4.25±0.25 / 0.12±0.01 / na / 0.34 / Tierney 1994
♂GE♀H / 0 / -- / -- / -- / -- / -- / Tierney 1994
♂H♀GE / 1 / 100% / 44.50 / 0.39 / na / 0.14 / Tierney 1994
♂H♀H / 4 / 50% / 54.00±42.50 / 0.14±0.01 / na / 0.63 / Tierney 1994