Use and avoidance of occupied hosts as a dynamic process in tephritid flies

26Maternal care is a basic family value in many insect species, including many phytophagous forms. Phytophagous insects typically express a simple type of maternal care by choosing where their offspring will develop. A number of species, for example, avoid laying eggs at sites that have been exploited by conspecifics (Table l), ^88,104,110 behavior commonly thought to minimize the level of intraspecific competition incurred by a female’s progeny. Intraspecific competition is well-documented in phytophagous species, particularly those that spend part of their life cycle inside stems, buds, fruits, or seeds. ^{5,20,119-121,125,135} It is therefore not surprising that phytophagous insects commonly avoid use of hosts occupied by conspecifics. Nevertheless, five major qualifications must be made with regard to the notion that avoidance of exploited hosts is a general phenomenon with obvious fitness value in phytophagous species where the host represents a relatively limited resource: 1) only rarely has explicit evidence been provided that avoidance behavior has fitness value; ^5,97 2) theory based on other host-specific insects predicts that level of avoidance should depend strongly on an individual’s egg load and level of experience; ^57,58,60 3) in species shown to avoid use of exploited hosts, level of avoidance can be highly variable; ^6,48,63,68 4) a number of species appear not to avoid use of exploited hosts at all; ^{44,48,88,89,102,112,1} is 5) certain species, far from avoiding use of exploited hosts, prefer them as sites of oviposition. ^78,80,124 In this review, a phytophagous insect’s responses to exploited hosts is viewed as a dynamic process both in a behavioral and an evolutionary sense. With special attention to frugivorous flies in the family Tephritidae, factors that might dispose insects toward either selective avoidance or selective use of exploited hosts are enumerated.