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The Effect of Pheromones on Anemotaxis

Pheromone can have an impactful role on insects. In this article, we discuss how pheromones influence insect behavior.

The effect of pheromones on anemotaxis has been examined in several species of insects. Field observations often indicate that the number of individuals arriving at pheromone source decreases as the wind velocity decreases below some threshold value. In the scarabaeid beetle, Rhopaea magnicomis (Blackburn), males exposed to sex pheromone ew at random when winds of less than 135 cm/sec were present, but with an increase in wind velocity to 225 cm/sec, males were observed ying toward the source (Soo H00 and Roberts 1965). Butler and Fairey (1964) noted that when drones of the honey bee, Apis mellifera L., hovered around a queen or a synthetic pheromone source suspended in air, they dispersed when the wind veloc- lty became low or lacking. Drones re-appeared when the air velocity increased to uhove 50 cm/sec. In the introduced pine sawy, Diprion similis (Hartig), large numbers of males were observed ying to a female sex pheromone source when wlnd velocities were above 90 cm/sec; fewer males approached the source at veloc- ltles less than this value (Casida et al. 1963). The decreased number of individuals reaching the pheromone source when air velocities were low might be attributed to the insects’ inability to detect sideslippage visually, since lower wind velocltles result in less relative side slippage when the insects’ ight speed remains constant. This occurs in pheromone olfactory detection.

The hypothetical anemotactic orientation sequence is as follows. The anemotactlc response is initiated when the insect perceives an above threshold concentration of molecules. The insect continues to y upwind as long as it remains within the

Upon sensing this sideslippage information, the individual is supposed to make compensatory turning responses in order to maintain upwind ight. The ability of an insect to detect sideslippage when it ies at an angle to the wind then becomes a determining factor in utilizing anemotaxis. Later studies on A. aegypti and on the vinegar y, Drosophila melano- gaster (Meigen), have further demonstrated the need for visual contact with the substratum in maintaining an anemotactic pheromone orientation (Kellogg et al. 1962; Wright 1962, 1964).

Insects of many species make prominent crosswind casts while ying along a chemical trail. This results in a zigzag ight pattern (Dethier 1947; Steiner 1953; Danzer 1956; Kellogg et al. 1962; Rudinsky and Daterman 1964; Traynier 1968; Cole 1970; Farkas and Shorey 1972), the probable function of which will be discussed below. For some species, the zigzag ight pattern may be eliminated when the pheromone chemical aerial trail is articially disrupted and the insect is exposed to an air ow carrying a near uniform cross-sectional distribution of molecules (Kellogg et al. 1962; Wright 1964; Traynier 1968; Dahm et al. 1971). In such cases, the pheromone-stimulated insect may y upwind in a fairly direct manner, presumably by means of anemotaxis.

Recently, Farkas and Shorey (1972) have demonstrated that males of the pink bollworm moth, Pectinophora gossypiella (Saunders), utilize a mechanism other than anemotaxis in steering to a sex pheromone source. Interference with possible visual cues from the substratum failed to inhibit individuals from ying to the pheromone source. Likewise, when a chemical aerial trail was presented to the moths in a ight tunnel and the air movement then eliminated, the insects were able to y along the motionless trail to the vicinity of the source.

Article Tags: Pheromone Source

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Alexander P a blogger from Los Angeles that studies pheromones.

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