When important agricultural pests are omnivores instead of strict herbivores, their impact on the host plant may change as the omnivore shifts between consumption of plants and consumption of prey. Lygus hesperus, a key pest of cotton, is known from laboratory and field studies to be an omnivore, but no field studies have ever quantified the importance of predation as a source of food. Cotton growers have long considered the impact of L. hesperus on cotton to be enigmatic, because sometimes crop damage seems to be higher or lower than would be expected based upon the density of L. hesperus estimated through sweep net samples. Here, we conducted focal observations of L. hesperus foraging freely in the field to quantify the relative importance of predation versus herbivory as food resources and to determine whether omnivory was sufficiently common that it might underlie the “Lygus enigma.” In observations of 84 individuals over a total of 56.7 h, we did not observe any predation events. Observations conducted in the laboratory under continuous magnification also yielded no evidence of predation, suggesting that we were not failing to detect predation events on small or cryptic prey in the field. Thus, L. hesperus expresses predatory behavior at most very infrequently and develops essentially as an herbivore in California cotton. We did, however, find that adult male L. hesperus spend more of their time resting and spend less time on the vulnerable reproductive structures of the cotton plant compared with nymphal stages or adult females. Further work on the Lygus enigma will examine the differential ease of sampling different L. hesperus life stages and the possibility that they contribute unequally to crop damage.
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