The laboratory colony of boll weevils historically located in Starkville, Mississippi was relocated to Edinburg, Texas in 2000. A new strain based on Lower Rio Grande Valley, Texas, field-collected weevils has also recently been established in Edinburg, Texas. Differences in untreated and malathion induced mortality between the historic Mississippi strain and the new Texas strain both reared with modified Texas rearing procedures are presented. Additionally, differences between the Mississippi and Texas colonies of the historic strain produced with Mississippi and Texas procedures respectively are discussed.

The Texas reared Mississippi strain exhibited higher mortality in untreated control populations and appeared to be more susceptible to malathion exposure compared to the recently established Texas reared Lower Rio Grande Valley strain. Differences between Mississippi and Texas colonies of the historic Mississippi strain appear evident in size and survival rates.

The differences between the two strains appear substantial, as do the differences between colonies of the Mississippi strain reared in Mississippi and Texas. The differences between strains are likely genetic. However, the differences between colonies are apparently a result of rearing procedures. These differences should be carefully considered when comparisons of data based on weevils from the two strains or from the two colonies with different rearing procedures are conducted.