IB Biology HL 4.1.6 Negative feedback control Question Bank

The prickly pear cactus (Opuntia stricta) was first recorded in Kruger National Park, South Africa, in 1950 . It spread rapidly, mainly through seeds being dispersed by baboons and elephants.

In 1997, the cactus moth (Cactoblastis cactorum) from South America was introduced into the area as a biological control. The larvae of the moth feed on the cactus. The graph shows the number of cladodes (flattened stem sections) of cactus found per $\mathrm{m}^{2}$ in the years before and after the introduction of the cactus moth.

Explain the change in numbers of the cactus moth throughout the study period.