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The Best Pheromones are Used by Predators

The best pheromones are used by predators which attack and consume adult beetles on a new host as well as ovipositing on the bark of infested trees so that their larvae will be near their prey, the de...

The best pheromones are used by predators which attack and consume adult beetles on a new host as well as ovipositing on the bark of infested trees so that their larvae will be near their prey, the developing bark beetle brood. Although Furniss and Schmitz (1971) did not demonstrate that Derzdroctonus pseudotsugae pheromones attracted any more clerids or ostomids than host terpenes, subsequent studies resulted in large catches of the clerid Thtmasimus Lmdatulus Wolc. to frontalin (table 8.2). In fact, the high response rates to frontalin by Trypodendron Lmdatulus and Thanasimus dubius (Fab.) and by Temnochila chlorodia (Mann.) to exobrevicomin (table 8.2), have provoked questioning of proposed aggregation pheromone control programs since they could remove large numbers of predators from the forest.

The parasitic wasp, Tomicobia tibialis Ashmead, is nearly specic to species (Bedard 1965) and must locate incoming beetles on the bark surface so it can mount the beetles and oviposit through the pronotum or elytra. Lastly, the y, Medetera bistriata Parent, oviposits on the bark around newly formed Dendrotonus frontalis or avulses Eichhoff galleries and young larvae enter the galleries to feed on scolytid larvae (Thatcher 1960).

Curiously, Pitman and Vité (1971) recorded only a marginal response of Eurus lecontei (Wolcott) to the aggregating pheromones frontalin and exo-brevicomin (fewer than to myrcene), despite their coincident arrival with their prey, Dendroctonus brevicomis, on a host tree under mass attack (Berryman 1970). Moreover, Temnochila chlorodia preys on a large number of scolytid species as well as on buprestids and cerambycids, despite the apparent lack of brevicomin in the phero- mone complex of such genera as Ips. Clearly we have yet much to learn about the precise kairomone orientation mechanisms for most early arriving parasites and predators. Such knowledge must probably await our complete understanding of scolytid aggregation pheromones according to

One might hypothesize that the parasitic, predaceous or commensal associates would follow a similar generalized sequential type of behavior (g. 8.2) to the scolytids themselves (g. 8.l)*. One may note that two of the accepted phases of host selection for parasitoids, host habitat nding and host nding (Doutt 1965) are borrowed and extended to apply to predators and commensals. Literally speak- ing, host nding need not be practiced by commensals which live in the gallery of scolytids, but in actual fact most species are so closely associated with the scolytids that actual contact would appear inevitable. One might expect that asso- ciated insects would utilize bark beetle pheromones in the orientation process. However, there are several means by which they could nd the host tree. If they arrive early in the phase of scolytid colonization they could rely on the same primary attraction mechanisms as the scolytids themselves. Included in this group would be most of the insects which compete for or share host tissue.

If the associates arrive after the scolytids are established in the new host, they‘ could also respond to stimuli from the host plant in its altered state following scolytid attack. For example, Fitzgerald and Nagel (1972) doubt that the common dipteran predator of scolytid larvae, Medetera aldrichii Wh.Free Web Content, responds to bark beetle pheromones ‘since ovipositing M. aldrichii are present in the eld after prey species have ceased pheromone production’.

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Alexander P is a blogger that studies pheromones. He is from Los Angeles, CA.

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