Are pollinating hawk moths declining in the Northeastern United States? An analysis of collection records

Abstract

Increasing attention to pollinators and their role in providing ecosystem services has revealed a paucity of studies on long-term population trends of most insect pollinators in many parts of the world. Because targeted monitoring programs are resource intensive and unlikely to be performed on most insect pollinators, we took advantage of existing collection records to examine long-term trends in northeastern United States populations of 26 species of hawk moths (family Sphingidae) that are presumed to be pollinators. We compiled over 6,600 records from nine museum and 14 private collections that spanned a 112-year period, and used logistic generalized linear mixed models (GLMMs) to examine long-term population trends. We controlled for uneven sampling effort by adding a covariate for list length, the number of species recorded during each sampling event. We found that of the 22 species for which there was sufficient data to assess population trends, eight species declined and four species increased in detection probability (the probability of a species being recorded during each year while accounting for effort, climate, and spatial effects in the GLMMs). Of the four species with too few records to statistically assess, two have disappeared from parts of their ranges. None of the four species with diurnal adults showed a trend in detection probability. Two species that are pests of solanaceous crops declined, consistent with a seven-fold drop in the area planted in tobacco and tomato crops. We found some evidence linking susceptibility to parasitoidism by the introduced fly Compsilura concinnata (Tachinidae) to declines. Moths with larvae that feed on vines and trees, where available evidence indicates that the fly is most likely to attack, had a greater propensity to decline than species that use herbs and shrubs as larval host plants. Species that develop in the spring, before Compsilura populations have increased, did not decline. However, restricting the analysis to hawk moth records from areas outside of a “refuge” area where Compsilura does not occur did not significantly increase the intensity of the declines as would be predicted if Compsilura was the primary cause of declines. Forests have recovered over the study period across most of the northeastern U.S., but this does not appear to have been a major factor because host plants of several of the declining species have increased in abundance with forest expansion and maturation. Climate variables used in the GLMMs were not consistently related to moth detection probability. Hawk moth declines may have ecological effects on both the plants pollinated by these species and vertebrate predators of the moths.

A window to the world of global insect declines: Moth biodiversity trends are complex and heterogeneous

“…In two studies, body size (forewing length) was the single best predictor of declining populations (70,71). Reports from the northeast United States also draw attention to the decline of larger moths (72,73). Other traits shared by declining moths include univoltinism, short flight seasons, low dispersal ability, and overwintering in the egg stage (21,67,68,70,71,74).…”

Historical collections as a tool for assessing the global pollination crisis

“…However, achieving this requires adequate funding [35]. Where digitization has been completed, the data provide a rich source of information, allowing assessment of the current status and long-term trends of pollinator populations [18,20,36]. This is despite the fact that museum collections often have a number of biases, including unknown sampling effort, personal interests of collectors and the curatorial…”

Moth diversity (Lepidoptera: Heterocera) of Banaras Hindu University, Varanasi, India: a preliminary checklist

“…Several factors can be attributed to the worldwide decline in moth population including habitat loss, degradation and fragmentation, agricultural intensification, changes in woodland management, urbanization, chemical pollution, artificial light at night and climate (Dennis et al, 2019). A number of plant species depend exclusively on one or a small number of moth species for pollination and a decline in those moth population and their diversity might lead to a negative impact in the plant communities they pollinate (Young et al, 2017).…”