Which of the following is a natural factor that helps control insect pests?

The correct choice is predation and parasitism, which are considered natural factors in pest control. Predators are organisms that consume pest species, effectively reducing their populations. For example, ladybugs feed on aphids, and parasitic wasps lay their eggs in or on pest insects, leading to their demise. These natural methods of control are integral to integrated pest management (IPM) strategies, as they leverage existing ecological relationships to maintain pest levels without the use of synthetic chemicals.

Chemical treatments involve the application of pesticides, which are not considered a natural method of control. Mechanical barriers, such as nets or physical traps, are tactics used to prevent pest access but do not involve natural processes. Genetic modifications relate to biotechnology and involve altering the genetic structure of plants or organisms to provide pest resistance, which is not a natural method.