No abstract

In this study we investigated the effects of two naturally occurring beta‐carboline alkaloids and two synthetic tricyclic antidepressants on the growth and food consumption of fifth instar larvae of the cabbage looper, Trichoplusia ni Hübner (Lepidoptera: Noctuidae). In artificial diets at high concentrations (3,000 ppm), harmane, amitriptyline, and imipramine reduce growth and feeding; harmane reduced feeding consistently at a lower concentration (200 ppm). In animals other than insects, beta‐carboline alkaloids inhibit monoamine oxidase (MAO) activity and thus affect rates of disposition of serotonin and other monoamine neurotransmitters. Because brain serotonin levels are associated with variation in rates of carbohydrate and protein intake in insects, the effects of beta‐carboline alkaloid ingestion on dietary self‐selection behavior were examined. Choosing between diets lacking carbohydrate but containing protein and diets lacking protein but containing carbohydrate, larvae consumed a greater proportion of diet containing protein but lacking carbohydrate in the presence of harmane than in its absence. These results are consistent with beta‐carboline alkaloid‐mediated persistence of serotonin in the brain due to MAO inhibition. Alternatively, these results could reflect alkaloid‐mediated peripheral inhibition of sucrose taste receptors influencing ingestive behaviors. That beta‐carboline alkaloid ingestion is associated with changes in feeding behavior is consistent with a possible defensive role for these compounds in plant foliage.

Prospects of global increases in extreme weather change provide incentive to examine how such change influences animal behavior, for example, behavior associated with resource use. In this study, we examined how oviposition behavior in a southern Arizona population of pipevine swallowtails (Battus philenor L.) responded to changes in their Aristolochia host resource and vegetative background caused by the North American monsoon system. Summer monsoon rains resulted in a flush of non-host vegetation and a more than doubling in rate of landings by host-searching females on non-host vegetation. Rates of discovery of the host species A. watsoni Woot. Standl. decreased by 50% after monsoon rains. Rains did not alter host density appreciably, but resulted in significant increases in host plant size and new growth, two indicators of host suitability for B. philenor larvae. After the rains, mean clutch size on individual host plants increased by a factor of 2.5; the mean proportion of host plants encountered on which a female laid eggs also increased significantly. Females were discriminating about the host plants on which they laid eggs after alightment; plants accepted for oviposition were larger, bore more new growth, and bore fewer larvae than rejected plants. Contrary to predictions from foraging theory, degree of discrimination did not change seasonally. Finally, the rate at which eggs were laid increased seasonally, suggesting that oviposition rates were limited more before monsoon rains by the relatively low quality of hosts than they were after the rains by the relatively low rate at which hosts were found. This latter result suggests that, while butterflies possess behavioral flexibility to respond to extreme weather change, such flexibility may have limits. In particular, expected increases in the severity and frequency of droughts may result in reduced oviposition rates, reductions that could have adverse demographic consequences.