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.
Some historians differentiate between a first Great Migration (1916â1930), which saw about 1.6 million people move from mostly rural areas to northern industrial cities, and a Second Great Migration (1940â1970), which began after the Great Depression and brought at least 5 million peopleâincluding many townspeople with urban skillsâto the north and to California and other western states.