No Detectable Insecticide Resistance in Swallow Bugs (Hemiptera: Cimicidae) Following Long-Term Exposure to Naled (Dibrom 8)

Birds of a Feather Flock Together: Extent of Long-Term Consistency of Colony-Size Choice in Cliff Swallows

Explaining why animal groups vary in size is a fundamental problem in behavioral ecology. One hypothesis is that life-history differences among individuals lead to sorting of phenotypes into groups of different sizes where each individual does best. This hypothesis predicts that individuals should be relatively consistent in their use of particular group sizes across time. Little is known about whether animals’ choice of group size is repeatable across their lives, especially in long-lived species. We studied consistency in choice of breeding-colony size in colonially nesting cliff swallows (Petrochelidon pyrrhonota) in western Nebraska, United States, over a 32-year period, following 6,296 birds for at least four breeding seasons. Formal repeatability of size choice for the population was about 0.41. About 45% of individuals were relatively consistent in choice of colony size, while about 40% varied widely in the colony size they occupied. Birds using the smaller and larger colonies appeared more consistent in size use than birds occupying more intermediate sized colonies. Consistency in colony size was also influenced by whether a bird used the same physical colony site each year and whether the site had been fumigated to remove ectoparasites. The difference between the final and initial colony sizes for an individual, a measure of the net change in its colony size over its life, did not significantly depart from 0 for the dataset as a whole. However, different year-cohorts did show significant net change in colony size, both positive and negative, that may have reflected fluctuating selection on colony size among years based on climatic conditions. The results support phenotypic sorting as an explanation for group size variation, although cliff swallows also likely use past experience at a given site and the extent of ectoparasitism to select breeding colonies.

Ecological correlates of group integrity among dispersing cliff swallows

Breeding colonies of birds represent groups of individuals that associate during one breeding season, at least partially dissociate for the non-breeding season, and may re-associate the next year through collective settlement at another breeding site. Little is known about the extent to which colonial birds maintain group integrity when occupying different sites in different years or the benefits of long-term associations among colonial individuals. For cliff swallows (Petrochelidon pyrrhonota) in western Nebraska, USA, we examined ecological correlates and potential benefits associated with group integrity. Using a dataset of over 25,000 individuals, we found that associations between dispersing cliff swallows were greater than would be predicted by purely random settlement among colony sites. The extent of group integrity varied widely among sites, with birds seeming to settle together more often at sites with fewer ectoparasites and at colonies similar in size and closer in physical proximity to the one they had previously occupied. Some associations of birds lasted three years in which they used a different site each year. Successful colonies had higher levels of group integrity among their settlers than did colonies that failed completely. Cliff swallows that were known to have settled with at least one conspecific from the previous year's site had a higher survival the next year than those not known to have settled with past residents. The results are consistent with cliff swallows choosing colonies based in part on parasite load and with sorting among colonies based on the birds' preferences for colonies of certain sizes.

Variation in neophobia among cliff swallows at different colonies

Animal groups often represent nonrandom subsets of individuals, and increasing evidence indicates that individuals may sort among groups based on their personalities. The size of a group can predict its personality composition in some species due to differential suitability of a personality for groups of certain sizes, and the group itself may function more effectively if particular personality types are present. We quantified cliff swallow (Petrochelidon pyrrhonota) behavioral measures using linear and generalized linear mixed models to identify whether they: (1) varied among individuals within colonies and among colonies, (2) were related to reproductive success, and (3) predicted levels of parental care. Significant among-individual and among-colony site variation in a cliff swallow's latency to enter its nest when presented with a novel stimulus was revealed. We also found significant among-individual variation in the number of attacks directed toward a novel stimulus at the nest and in the response to broadcast of a cliff swallow alarm call recording, but among site variation in these measures was not significant. We did not find evidence for behavioral syndromes linking the personalities measured. Differences among individuals in latency to enter the nest and the number of attacks were not significantly related to reproductive success or to the extent to which birds fed their nestlings. However, extent of nestling feeding was significantly predicted by the number of mist net captures. The limited evidence in general of systematic variation in the behavior we measured among cliff swallow colonies may reflect the different and sometimes opposing selection pressures on behavior in different social environments. Future work should perhaps examine variation in other behavioral traits, such as foraging, in cliff swallow colonies of different sizes.

Distribution and Frequency of Pyrethroid Resistance-Associated Mutations in Host Lineages of the Bed Bug (Hemiptera: Cimicidae) Across Europe

For over two decades, the bed bug, Cimex lectularius L. (Hemiptera: Cimicidae) has been undergoing a dramatic global resurgence, likely in part to the evolution of mechanisms conferring resistance to insecticides. One such mechanism is knock-down resistance (kdr), resulting from nonsynonymous mutations within the voltage-gated sodium channel (VGSC) gene. To date, three mutations have been identified in C. lectularius, V419L, L925I, and I936F. Using Sanger sequencing, the frequency and distribution of these VGSC mutations across 131 populations collected from the bat-associated and human-associated lineages of C. lectularius found in Europe are documented. All populations from the bat-associated lineage lacked mutations at the three sites. In contrast, the majority of populations associated with humans (93.5%) possessed the mutation at the L925I site. The I936F mutation, previously only reported in Israel and Australia, was found in nine populations spread across several European countries, including the Czech Republic and Switzerland. The high frequency of kdr-associated resistance already reported in C. lectularius and the occurrence and broad geographic distribution of this additional VGSC mutation, questions the continued use of pyrethroids in the treatment of infestations.

Parasites favour intermediate nestling mass and brood size in cliff swallows

A challenge of life-history theory is to explain why animal body size does not continue to increase, given various advantages of larger size. In birds, body size of nestlings and the number of nestlings produced (brood size) have occasionally been shown to be constrained by higher predation on larger nestlings and those from larger broods. Parasites also are known to have strong effects on life-history traits in birds, but whether parasitism can be a driver for stabilizing selection on nestling body size or brood size is unknown. We studied patterns of first-year survival in cliff swallows (Petrochelidon pyrrhonota) in western Nebraska in relation to brood size and nestling body mass in nests under natural conditions and in those in which hematophagous ectoparasites had been removed by fumigation. Birds from parasitized nests showed highest first-year survival at the most common, intermediate brood-size and nestling-mass categories, but cliff swallows from nonparasitized nests had highest survival at the heaviest nestling masses and no relationship with brood size. A survival analysis suggested stabilizing selection on brood size and nestling mass in the presence (but not in the absence) of parasites. Parasites apparently favour intermediate offspring size and number in cliff swallows and produce the observed distributions of these traits, although the mechanisms are unclear. Our results emphasize the importance of parasites in life-history evolution.

Why come back home? Breeding-site fidelity varies with group size and parasite load in a colonial bird

Fidelity to a past breeding site is widespread among animals and may confer both costs and benefits. Colonial species occur at specific sites that can accommodate multiple breeders, and the choice of whether to return to last year's site or disperse elsewhere can affect colony site use, the colony size distribution and individual fitness. For the colonial cliff swallow, Petrochelidon pyrrhonota, which occupies colonies of widely different sizes, we used a 30-year field study in western Nebraska to investigate how the extent of infestation by ectoparasites and colony size affected breeders' colony site fidelity between years. We compared philopatry at colonies where parasitic swallow bugs, Oeciacus vicarius, had been removed by fumigation with that at nonfumigated sites exposed to natural levels of ectoparasites. About 25% of birds at nonfumigated colonies returned to their previous year's site, whereas about 69% of birds at fumigated colonies did so. Site fidelity was greatest at nonfumigated sites that changed the least in size between years. Birds were less likely to return to a nonfumigated site as the colony there became increasingly larger. Individuals philopatric to both nonfumigated and fumigated sites resided in colonies more similar in size between years than did dispersing birds. Most cliff swallows settled within 6 km of their previous year's site, indicating that many nonphilopatric birds still may have had some familiarity with the local landscape surrounding the site to which they moved. Removal of ectoparasites at a site allows large colonies to persist there perennially, probably contributing to higher philopatry because such large colonies are rare and would have been difficult to find had the residents dispersed. Cliff swallows are likely to be sensitive to both colony size and general familiarity with a given site or landscape region, and probably integrate these with other cues to select breeding colonies.