Assessing pollen nutrient content: a unifying approach for the study of bee nutritional ecology.

Poor nutrition and landscape changes are regularly cited as key factors causing the decline of wild and managed bee populations. However, what constitutes 'poor nutrition' for bees currently is inadequately defined. Bees collect and eat pollen: it is their only solid food source and it provides a broad suite of required macro- and micronutrients. Bees are also generalist foragers and thus the different pollen types they collect and eat can be highly nutritionally variable. Therefore, characterizing the multidimensional nutrient content of different pollen types is needed to fully understand pollen as a nutritional resource. Unfortunately, the use of different analytical approaches to assess pollen nutrient content has complicated between-studies comparisons and blurred our understanding of pollen nutrient content. In the current study, we start by reviewing the common methods used to estimate protein and lipids found in pollen. Next, using monofloral Brassica and Rosa pollen, we experimentally reveal biases in results using these methods. Finally, we use our collective data to propose a unifying approach for analysing pollen nutrient content. This will help researchers better study and understand the nutritional ecology-including foraging behaviour, nutrient regulation and health-of bees and other pollen feeders. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Effect of queen number on colony-level nutrient regulation, food collection and performance in two polygynous ant species.

There is growing appreciation for how social interactions influence animal foraging behavior, especially with respect to key nutrients. Ants, given their eusocial nature and ability to be reared and manipulated in the laboratory, offer unique opportunities to explore how social interactions influence nutrient regulation and related processes. At the colony-level, ants simultaneously regulate their protein and carbohydrate intake; a regulation tied to the presence of larvae. However, even though 45% of the approximately 10,000 ant species are polygynous, we know little about the influence of queen number on colony-level foraging behavior and performance. Here we explored the direct effects of queen number on colony-level protein-carbohydrate regulation, food collection, survival, and brood production in two polygynous ant species (Nylanderia fulva and Solenopsis invicta). For both species we conducted choice and no-choice experiments using small experimental colonoids (20 workers) with 0, 1, or 2 queens. Both species regulated their relative intake of protein and carbohydrate around a P1:C2 mark. However, only N. fulva responded to the addition of queens, increasing overall food collection, biasing intake towards carbohydrates, and over-collecting imbalanced foods. N. fulva also exhibited reduced survival and reproduction on protein-biased foods. In contrast, S. invicta showed no response to queen number and reduced food collection on the protein-biased diet while maintaining high survival and reproduction. Our results demonstrate the potential for queens of some ant species to impact colony-level foraging and performance, with interspecific variation likely being shaped by differences in life history traits.

Foliar herbivory increases sucrose concentration in bracteal extrafloral nectar of cotton.

Cultivated cotton, such as Gossypium hirsutum L., produces extrafloral (EF) nectar on leaves (foliar) and reproductive structures (bracteal) as an indirect anti-herbivore defense. In exchange for this carbohydrate-rich substance, predatory insects such as ants protect the plant against herbivorous insects. Some EF nectar-bearing plants respond to herbivory by increasing EF nectar production. For instance, herbivore-free G. hirsutum produces more bracteal than foliar EF nectar, but increases its foliar EF nectar production in response to herbivory. This study is the first to test for systemically induced changes to the carbohydrate composition of bracteal EF nectar in response to foliar herbivory on G. hirsutum. We found that foliar herbivory significantly increased the sucrose content of bracteal EF nectar while glucose and fructose remained unchanged. Sucrose content is known to influence ant foraging behavior and previous studies of an herbivore-induced increase to EF nectar caloric content found that it led to increased ant activity on the plant. As a follow-up to our finding, ant recruitment to mock EF nectar solutions that varied in sucrose content was tested in the field. The ants did not exhibit any preference for either solution, potentially because sucrose is a minor carbohydrate component in G. hirsutum EF nectar: total sugar content was not significantly affected by the increase in sucrose. Nonetheless, our findings raise new questions about cotton's inducible EF nectar responses to herbivory. Further research is needed to determine whether an herbivore-induced increase in sucrose content is typical of Gossypium spp., and whether it constitutes a corollary of systemic sucrose induction, or a potentially adaptive mechanism which enhances ant attraction to the plant.

Facultative Viviparity in a Flesh Fly (Diptera: Sarcophagidae): Forensic Implications of High Variability in Rates of Oviparity in Blaesoxipha plinthopyga (Diptera: Sarcophagidae).

Flesh flies are major primary consumers of carrion and are commonly found on human remains. Due to this latter feeding habit, their development rates can be used to provide temporal information in forensic investigations. This is usually done by referencing published flesh fly development datasets. Flesh flies are typically assumed to be strictly viviparous and datasets reporting their development rates therefore start at the first larval instar. However, an increasing number of studies has identified oviposition by flesh flies, including the forensically relevant species Blaesoxipha plinthopyga Wiedemann. To assess the impact of egg-laying behavior on casework, oviparity rates and time before larval hatching were assessed under controlled laboratory conditions that reflect common casework conditions in Harris County, Texas. We demonstrated systematic deposition of viable eggs but at a very variable rate between samples. Similarly, the duration between oviposition and larval hatching was highly variable, with some eggs taking more than a day to hatch after deposition. These results highlight the need to account for embryonic development in forensic investigations including B. plinthopyga and advocates for the re-evaluation of the assumed strict viviparity of the Sarcophagidae.

Influence of social interactions on the response to social cues in spiderlings.

Mutual attraction is one central mechanism involved in the maintenance of cohesion in group-living species and relies on a modulation of individual behaviours in response to the presence of conspecifics. Social markers left in the environment can play an additional role in the modulation of behaviours and can substantially impact the cohesion of social groups. In this study, our objective was to examine the interplay between the presence of social cues and the individual responsiveness to conspecifics in spiderlings. Spiders are relevant models to address this issue as juveniles lay silk draglines during their displacements and display a transient gregarious phase. We introduced single or pairs of spiderlings in an experimental arena covered with different amounts of silk. Our results indicated that the probability of moving increased with the presence and the quantity of silk in single individuals. In contrast, we did not find evidence for any influence of the quantity of silk on interacting spiderlings and we showed that social interactions inhibited the individual response to social markers. Overall, our study suggests that the influence of social interactions on the modulation of individual behaviours prevailed over the presence of social cues. We discussed our results in the framework of chemical communication to explain the interplay between social cues and social interactions on the modulation of individual behaviours.