Upwind anemotaxis

The explanation advanced by Kennedy and Marsh (1974) for the zigzag behavior was that the successive turns were initiated after the loss of the scent the turn carried the moth back towards the direction where the scent was last sensed. (The direction towards the source, however, would be detected by the optomotor response discussed previously.) Gomplementary evidence that such turns are initiated by the loss of the plume come from Traynier s (1968) wind tunnel observations with the moth Anagusta kuhniella in homogeneous pheromone clouds moths were reputed to fly upwind in a straight path (see also the end of this section). 

Tests designed to compare the flight track of males in narrow discrete plumes vs. homogenous clouds of pheromone in Adoxophes orana (Kennedy et al., 1980, 1981, see Fig. 5.1) and L. dispar (Garde and Grankshaw, 1983), unlike 

Trannier s 1968 observations, have shown that the zigzag path occurs under both conditions, in contradiction to the mechanism proposed by Kennedy and Marsh (1974). Lateral reversals, then, seem to occur in the presence of wind-borne pheromone and thus represent an internally generated pattern of flight. 

The visual effects generated in both situations are similar in terms of the amount of angular deflection, although the path of the visual field across the eyes would be quite different. If the insect s body is aligned with the course direction, the flow of the visual field beneath the eyes alternates at an angle relative to the head-body axis that is equal to the drift angle (Marsh et al., 1978). 

Another explanation for the zigzag path is that it allows the moth to fly up the plume by sequential sampling of the pheromone plume s spatial structure when the wind drops below the anemotactic threshold. This strategy will be explored in Section 5.3.2. Another consideration is that a zigzag path (noting both the lateral and the vertical components) would increase the probability recontacting chemical stimulus after loss of the scent (Kennedy, 1978 David et al., 1982 see Section 5.2.6). 

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A female must search at random within a habitat until one of the stimuli important in host selection is encountered. As with insects responding to sex pheromones, some parasitoids respond to air movements and fly upwind (anemotaxis) (Edwards, 1954). Odors stimulate a klinokinetic response in Mormoniella (Edwards, 1954) whereas odors may stimulate chemotaxis in other species (Read et al., 1970). However, there has been relatively little data on the long range orientation of parasitoids. The cues that allow a parasitoid to orient to a potential host community presumably act from a distance. The types of stimuli that meet this criterion include electromagnatic radiation, sound, or odors. 

Terms such as anemotaxis and klinotaxis, while seemingly defining a reaction precisely, tend to promote the notion of single-solution orientation systems. Yet insects may well process the available information necessary for several mechanisms, selecting the anemotactic reaction, for example, only when there are sufficient anemo and visual cues and flight directly upwind provides continued contact with the chemical stimulus. Such terms also tend to camouflage the importance of non-chemical and idothetic inputs. 

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