Pheromones in insects can elicit a positive response
The response in pheromones in insects can vary widely in pest management. In this article, we will discuss the variabilities.
Pheromones in insects can elicit a positive response (Sonnet and Moser 1972). All but one of the 11 compounds were required in amounts 102 to 104 times greater than the pheromone to elicit a response. Information is not, however, available on the effects‘ of the male pheromones at the antennal receptor level.
For the southern pine beetle, all but one of 10 parapheromones of frontalin (1,5-dimethyl-6, 8-dioxabicyclo [3.2.l.] octane) were completely inactive in eld tests (Renwick 1970). The parapheromone 5,7-dimethyl-6, 8-dioxabicyclo [3.2.l.] octane had a slight additive effect on the field response of female southern pine beetles to frontalin and the host tree terpene oz-pinene. Eight of the paraphero- mones were investigated for their effects at the receptor level (Payne 1970, unpub- lished). All of the compounds were active in undiluted form (table 3.1). However, serial dilutions were not tested, so thresholds of response relative to frontalin are unavailable.
In comparison with lepidopterous species, a decrease or absence of behavioral response by the bark beetle is not necessarily correlated with the degree of differ- ence in structure between the parapheromone and the pheromone or electrophysiological response from the antenna. It is possible that different receptors are involved in the perception of the pheromone and the various parapheromones, thus accounting for the absence of behavioral response and the presence of receptor response. However, there is strong evidence that only one receptor is involved. EAGs from the southern pine beetle are nearly identical to frontalin and exobrevicomin (exo-7-ethyl-5-methyl-6, 8-dioxabicyclo [3.2.l.] octane: Silverstein et al. 1968), an ag- gregation pheromone of the western pine beetle, Dendroctonus brevicomis LeConte, and essentially a parapheromone of frontalin. The response to frontalin can be com- pletely eliminated by saturation of the receptors with a previous exposure to exo- brevicornin (Payne 1971, unpublished). The effect is reversible and prior exposure to frontalin will prevent response to exo-brevicomin. In addition, while antennal receptors for these compounds are adapted, response can still be elicited from ex- posure to unrelated compounds such as host tree terpenes, thus indicating that all receptors on the antenna are not blocked by saturation with one compound (table 3.2). †Learn more about†pheromone dispensers.
It is apparent that the correlation of pheromone structure to behavioral response is more difficult in bark beetles than other insects because in these beetles a mix- lure of compounds (pheromone(s) and host odors) is necessary to elicit behavioral responses.
A beetle produced compound alone can be essentially inactive, but become active in the presence of host tree terpene (Kinzer et al. 1969). However, at the antennal level both the pheromone and host tree terpene can be independently effective (Payne 1970). In comparison to some lepidopterous species it appears that stimulation of a given receptor in bark beetles does not mean that a given behavior in response will result. Apparently initiation of a behavioral response requires the integration of information from different receptors.
They are quite specific in the range of molecular structures to which they will respond. It can be said that the pheromone receptor functions as a molecular lter for molecules important in the life of the insect.
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ABOUT THE AUTHOR
Alexander P†is a blogger from Los Angeles that studies the role of pheromones.