Why you need a mixture of two endoparasitic wasps including Aphidius colemani and Aphidius ervi. they can reduce the crop damage by parasitizing and killing a mixed population of a variety of host species of aphids that are responsible for the crop damage.
In the major cities of the Midwest and Northeast, they found relatively high paying jobs in meatpacking plants, shipyards, and steel mills. The second significant cause of the Great Migration was the desire of black Southerners to escape segregation, known euphemistically as Jim Crow.
Between 300,000 and 1,000,000 African-Americans moved north during this perio â¦ d, largely in response to an increased number of unskilled factory job openings as northern manufacturers boosted production for World War I. Black migration between 1916 and the 1960s remained strong, except during the Great Depression.People in the South were obviously racist against the African  Americans, so during the Great Migration, the right to vote caused  a lot of controversy. This is because when the African Americans  moved to the Norht they were given the right to vote.