Keiji Takasu

The role of learning in adult food location by the larval parasitoid, Microplitis croceipes (Hymenoptera : Braconidae)

Wind tunnel experiments were conducted to determine roles of odor learning in food foraging of the larval parasitoid,Microplitis croceipes (Hymenoptera: Braconidae). Females that had neither fed on sucrose water nor experienced any odor and females that had experienced an odor without feeding failed to respond to any odors in a wind tunnel. Most of the females that had fed without an odor also did not respond to odors. However, most of the females that had experienced an odor during feeding on sucrose water flew to the odor. These results indicate that when females experience an odor during feeding, they learn to associate the odor with food and subsequently respond to the odor. As age of females increased, their response to an experienced odor increased, peaked 2 to 5 days after emergence, and then decreased. With an increasing number of odor experiences while feeding, accuracy of females choosing the experienced odor increased. Females that experienced an odor while feeding three to five times chose the experienced odor 90% of the time. When females experienced an odor while feeding five times, the memory of food associated odor lasted at least 2 days. When they experienced food with two odors successively, they could memorize both odors, and multiple experiences did not cause memory interference. Even when females had learned a food-associated odor, their response to the learned odor ceased after several visits on patches containing the odor but no food. Such “negative experience” may cause switching of food searching to new odors by females.

Olfactory associative learning of the pupal parasitoid Pimpla luctuosa Smith (Hymenoptera: Ichneumonidae).

Laboratory experiments were conducted to determine the role of learning in olfactory host searching by the ichneumonid pupal parasitoid, Pimpla luctuosa Smith. Females learned to associate novel odors such as vanilla and strawberry with hosts when they oviposited in at least several hosts with the odors. Repeated experiences of hosts with an odor increased the response of the experienced odor, and females that had experienced host odor seven times responded to the experienced odors 90% of the time. Although the response by females to a learned odor gradually decreased with increasing host-deprivation time, 60% of the females that had experienced host odor 7 days earlier still responded to the experienced odor. Females also learned two separate odors associated with hosts at a time and responded to both odors without a preference for one odor over the other. When trained two separate odors with hosts, females learned the second odor more quickly than the first odor. After females experienced several stings in “simulated hosts” with the previously learned odor, they ceased to respond to the learned odor, suggesting that repeated unrewarding experiences cause females to cease to respond to the learned odors.

Food odor learning by both sexes of the pupal parasitoid Pimpla alboannulatus uchida (Hymenoptera : Ichneumonidae)

Synovigenic parasitoids need nonhost foods such as floral and extrafloral nectar, honeydew, or pollen (Leius, 1960; Powell, 1986; Jervis and Kidd, 1986, 1996). Provision of such food increases the longevity and fecundity of females and the longevity of males (reviews, Jervis and Kidd, 1986, 1996). Field studies have also shown that the presence of food sources attracts parasitoids and increases parasitism (Powell, 1986; Grossman and Quarles, 1993). Although recent experimental studies have examined the food foraging behavior of parasitoids (Idris and Grafius, 1997; Patt et al., 1997), little is known about the mechanism by which parasitoids locate food sources. A few studies have shown that parasitoid females use olfactory or visual cues to locate food sources and that the preference for such cues of food sources is innate or induced by associative learning (Wäckers, 1994; Takasu and Lewis, 1996; Lewis et al., 1998; Patt et al., 1999). For example, the larval parasitoid Microplitis croceipes (Cresson) can learn food-associated odors. After given an odor while feeding on sucrose water several times, females

Host recognition by the tick parasitoid Ixodiphagus hookeri (Hymenoptera: Encyrtidae)

Abstract We conducted laboratory experiments to determine whether the tick parasitoid Ixodiphagus hookeri Howard uses chemicals of the host tick Amblyomma variegatum F. as host recognition cues. When given a piece of polyethylene sheet containing an air bubble (a dummy host) treated or untreated with hexane, I. hookeri females did not respond to the dummy. However, when females contacted the dummy host treated with hexane extracts from unfed nymphs, engorged nymphs, or unfed adults of the host ticks, they probed the dummy with their ovipositors. When given a choice of dummies treated with hexane extract of engorged nymphs, hexane, or nothing, they did not demonstrate any selective attraction for the dummy with hexane extract from engorged nymphs over the other dummies. A fraction (hexane 9: ether 1) of hexane extract from engorged nymphs strongly stimulated ovipositor probing by females. These results suggest that I. hookeri females use chemicals contacted on host ticks as host recognition cues.