Host discrimination marking and epideictic pheromones

Insects use varied mechanisms to achieve optimal density levels, including physical combat (Hubbell and Johnson, 1977), visual cues (Rothschild and Schoonhoven, 1977), accoustical cues (Russ, 1969), and chemical cues. The chemicals involved in regulating density or in preventing overcrowding are documented in detail by Prokopy et al. in Chapter 11. 

Salt (1934) was the first to show that parasitoids could discriminate between healthy hosts and parasitized hosts. Discrimination and marking of hosts has been controversial since authors investigating the same parasitoid reported 

Parasitoid marking pheromones, according to van Lenteren (1981) (i) prevent multiple ovipositions into the same host and consequent egg wastage, (ii) prevent host wastage because superparasitized hosts often die, resulting in death of the parasitoids, (iii) save time, particularly if the process of attack and oviposition are lengthy and (iv) initiate migration to more productive habitats when several marked hosts are encountered. 

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