A mathematical population model (exponential bivariate) was generated and validated to estimate the mean longevity (λ) and hatching period (δ) of nymphal instars of Phoetaliotes nebrascensis (Thomas), Melanoplus lakinus (Scudder), and Boopedon nubilum (Say). P. nebrascensis with 356 insects was most abundant, followed by 280 of M. lakinus, and 220 of B. nubilum; five nymphal instars were found for each species. The model fitted (F_{59, 59, 0.05} = 1.5399) to P. nebrascensis (s_v² / s_m² = 1.2), and M. lakinus (s_v² / s_m² = 0.9), but not to B. nubilum (s_v² / s_m² = 34.2), because this specie was less frequent. The λ values for these species were 7.05, 12.2, and 5.17 days, while δ had values of 33, 35, and 10 days; hatching periods were from 5 July to 7 August, 24 June to 29 July and 20–30 July. M. lakinus hatched before that B. nubilum and P. nebrascensis, and also had a longer hatching period than the other two species, so it was present during a longer period of time in pastures of Durango, Mexico.