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.
Save. Photos.com/Photos.com/Getty Images. Push and pull factors are used to explain why people choose to migrate. Anthropologists studying voluntary human migration have identified various factors that correlate, either positively or negatively, to the intensity of migration flow.his migration occurs because the push factors -- limited economic opportunities and lack of entertainment and diversions -- and pull factors -- jobs, cultural attractions, better services -- are both strong.