By presenting and analyzing the pest–predator model under insecticides used impulsively, two impulsive strategies in biological control are put forward. The first strategy: the pulse period is fixed, but the proportional constant E 1 changes, which represents the fraction of pests killed by applying insecticide. For this scheme, two thresholds, E 1 ∗∗ and E 1 ∗ for E 1 are obtained. If E 1⩾E 1 ∗ , both the pest and predator (natural enemies) populations go to extinction. If E 1 ∗∗<E 1<E 1 ∗ , the pest population converges to the semi-trivial periodic solution while the predator population tends to zero. If E 1 is less than E 1 ∗∗ but even if close to E 1 ∗∗ , there exists a unique positive periodic solution via bifurcation, which implies both the pest and the predator populations oscillate with a positive amplitude. In this case, pest population is killed to the maximum extent while the natural enemies are preserved to avoid extinction. The second strategy: the proportional constant E 1 is fixed ( E 1<E 1 ∗ firstly), but the pulse period changes. For this scheme, one threshold τ 0 for the pulse period τ is obtained. We can reach the same target as above by controlling the period impulsive effect τ< τ 0, even if close to τ 0. Our theoretical results are confirmed by numerical simulations.