Most insect parasitoids are related to two insect orders, Diptera and Hymenoptera, some having a specific host while others have a vast host range. As such, the opening chapter of Parasitoids: Biology, Behavior and Ecology discusses the influence of host preference and host specificity in biological control programs and their role in different biological control methods. The behavioral responses of parasitoids can determine the efficiency of a parasitoid species to control host pests. The functional response is one of the most important behavioral responses. The authors show that type II functional response is more common than the other types (I, III, IV and V) of functional response for most parasitoid species. In some research, type III functional response was also reported for parasitoids. The closing study hypothesized that conditioned parasitoids will parasitize more target hosts compared with individuals without prior conditioning. In conditioning experiments, females of the wasp Trichogramma cacoeciae, a generalist egg parasitoid, oviposited in Lobesia botrana eggs while exposed to L. botrana’s synthetic sex pheromone. Contrary to the hypothesis, this treatment failed to increase the parasitism rate in a subsequent exposure to the conditioned olfactory cue.