Sex differences in the foraging behavior of a generalist hawkmoth

Abstract

Within-species variation in pollinator behavior is widely observed, but its causes have been minimally investigated. Pollinator sex is associated with large differences in behavior that may lead to predictable differences in flower foraging, but this expectation has not been explicitly tested. We investigate sex-associated differences in nectar-foraging behavior of the hawkmoth Hyles lineata, using pollen on the proboscis as a proxy for flower visitation. We tested two predictions emerging from the literature:(1) the sexes differ in the flower species they visit, (2) females are more specialized in flower choice. We also examined potential drivers underlying these predictions by performing field and laboratory experiments to test whether males (3) switch among flower species more frequently, or (4) fly farther and therefore encounter more species than females. Consistent with prediction (1), pollen load composition differed between the sexes, indicative of visitation differences. Contrary to prediction (2), females consistently carried more species-rich pollen loads than males. (3) Both sexes switched between flower species at similar rates, suggesting that differences in floral fidelity are unlikely to explain why females are less specialized than males. (4) Males flew longer distances than females; coupled with larger between-site differences in pollen composition for females, this result suggests that sex differences in mobility influence foraging, and that females may forage more frequently and in smaller areas than males. Together, our results demonstrate that sex-associated foraging differences can be large and consistent over time, and highlight the importance of sex as a driver of variation in pollinator behavior.

Developmental temperature predicts body size, flight, and pollen load in a widespread butterfly

“…We were unable to find any existing data on the relationship between body size, flight, and pollen accumulation in butterflies. However, some hawkmoths show positive correlations between proboscis length and pollen load, and body size is positively correlated with proboscis length in many butterflies, suggesting that larger individuals may carry more pollen (Corbet, 2000; Kunte, 2007; Smith et al, 2022). Given the possible positive relationships between body size and pollen load, and between wing size and flight ability, we predicted that smaller‐winged/bodied P. rapae would visit fewer flowers or flower types and carry fewer pollen grains than larger‐winged/bodied conspecifics.…”

Mutualism has its limits: consequences of asymmetric interactions between a well-defended plant and its herbivorous pollinator

“…(b) Conflicts of interest limit mutualistic benefits to adult H. lineata moths Although H. lineata moths forage widely from flowers in many habitats [69][70][71], O. harringtonii plants provide important nectar resources for them in the shortgrass prairie of central Colorado, USA. Our prior experiments with H. lineata from this region show increased survival and fecundity of female moths after nectar meals [41].…”

Pollen accumulation on hawkmoths varies substantially among moth-pollinated flowers

“…While the specific causes of this loss are not clear from this study, we speculate that the majority is due to passive loss (Inouye et al, 1994) resulting from proboscis curling. In hawkmoths, curling the proboscis after feeding can result in substantial pollen movement and loss from this structure (Smith et al 2021). Anecdotally, repeated curling events were more likely to have occurred for 5-visit moths: after 1-3 visits to focal flowers in quick succession (during which there may not have been even 1 proboscis curl), moths often explored the rest of the cage and examined other parts of the plant before returning for the 4 th and 5 th visit.…”

“…For representative videos of visits to each plant species, see Supplement [S2]. After each trial was completed, moths were re-captured and pollen on the proboscis (see Figure 1) was removed using ∼2 mm 2 cubes of fuchsin gel (Kearns & Inouye, 1993), following the methods of Smith et al (2021). These cubes were then melted onto clean microscope slides with a cover slip.…”

“…As pollinators are unlikely to pick up a given plant’s pollen anywhere except from that plant’s flowers, pollen loads serve as a forensic record of which plants pollinators had visited during previous foraging bouts and can be collected from many more individuals than would be possible to observe. This technique is especially useful for studying the foraging of hawkmoths (Haber and Frankie 1989; Alarcón et al, 2008; Nilsson et al, 1987; Smith et al, 2021): as hawkmoths do not groom themselves or consume pollen, any pollen found on their proboscises is unlikely to be biased by decisions on which resources to collect (as seen in pollinators such as bees; e.g., Lunau et al, 2015). Drawing inferences beyond a given plant’s presence from these loads, however, requires several assumptions, the largest of which is that pollen from different flowers is acquired at relatively comparable rates.…”