Bimodal activity of diurnal flower visitation at high elevation

Pacific Northwest native plants and native cultivars, part I: pollinator visitation

Planting native flora is a popular conservation strategy for pollinators. When searching for native plants, consumers may encounter cultivars of native plants, which can have different phenotypic traits than plants found in wild populations ("wild-type native plants"). Previous research evaluating pollinator visitation to wild-type native plants and native cultivars has yielded mixed results, in terms of whether their visitation rates are similar or distinct. We established a garden experiment in Corvallis, Oregon, to examine pollinator visitation and utilization of Pacific Northwest native plant species and cultivars. Over 3 years, we collected and observed bees (Hymenoptera: Apoidea), butterflies (Lepidoptera: Papilionoidea), and syrphid flies (Diptera: Syrphidae) to understand (i) if plant pairs had different visitation rates, (ii) whether any pollinators were associated with differential visitation, and (iii) if specialist taxa preferred wild types over cultivars. Pollinator visitation rates varied by plant and pollinator groupings, but in comparisons between native plant and cultivar pairs, native plants were preferred 37.2% of the time (n = 29 comparisons), cultivars 7.7% of the time (n = 6), and there was no difference in 55.1% of comparisons (n = 43). Our pollinator community data found native plants had greater observed total pollinator richness (except for 1 tie) and bee richness than cultivars, though predicted richness varied. Specialist bees were collected more often from wild types. Cultivars with high visitation rates were minimally developed selections, as opposed to interspecific hybrids. Our results join a growing body of literature in suggesting wild-type native and minimally developed plants should be emphasized for supporting pollinator fauna.

Diptera Dwelling Aquatic and Terrestrial Habitats in an Alpine Floodplain (Amola Glacier, Italian Alps)

Among flying insects, Diptera were the main visitors and colonisers of aquatic and terrestrial habitats in an Alpine glacial floodplain (NE Italy) at 2400 m a.s.l. In all, 4317 dipteran adults were collected using different collection techniques in, on, and out of the water: pond and drift nets, and emergence and Malaise traps, with a different periodicity: biweekly and every three hours for four consecutive days, in early and late summer 2015. Thirty-eight families in all, and 56 species within seven Brachycera families, were identified. Specifically, Chironomidae (36%) within Nematocera and Empidoidea families (23%), and Muscidae (9%) within Brachycera, prevailed. Chironomidae seemed to emerge and fly mainly in late morning-early afternoon, while most Brachycera were more active in late afternoon. Some ecological notes are given for seven Brachycera families, including Muscidae as the predominant family of anthophilous dipterans and the most efficient pollinators in mountain habitats and in the deglaciated areas of the proglacial forelands. Three genera of Muscidae were found as the main representatives of these environments: Thricops Rondani, Spilogona Schnabl, and Phaonia Robineau-Desvoidy). Among these genera, noteworthy was the finding of Spilogona triangulifera (Zetterstedt) as being new to the Italian fauna.

The Functional Dilemma of Nectar Mimic Staminodes in Parnassia wightiana (Celastraceae): Attracting Pollinators and Florivorous Beetles

While floral signaling plays a central role in the reproductive success of all animal-pollinated plants, it may also attract herbivores eager to feed on flowers. False nectaries with glossy surfaces reflecting incident light may produce signals that attract floral visitors guiding their movements to and within the flower. Whether false nectaries also attract herbivores that lower the reproductive success of natural populations requires attention. In this study, we focus on Parnassia wightiana, a subalpine species with a whorl of staminodes that act as false nectaries attracting bees, flies, and herbivorous beetles. We tested the functions of staminodes using controlled manipulative experiments under field and lab conditions. We found a significant decrease in pollinator visits, and subsequent seed set, in flowers in which we removed staminodes or staminode apices confirming the function of these organs. In our natural populations, we found that a beetle, Nonarthra variabilis (Alticinae; Chrysomelidae), chews first on staminode apices, then it eats the entire staminodes and other flower parts, but rarely feeds on ovaries. Additional experiments suggested these beetles preferred staminodes to ovaries. Our results suggest this is a case of selective florivory, in which staminodes play a dual role, attracting pollinators and herbivores at the same time causing the attractive dilemma. Although selective florivory by beetles did not directly damage fruits, it influenced plant-pollinator interactions, decreasing reproductive success in plant populations. Our study highlights the importance of plant-pollinator-herbivore interactions in selecting floral traits.

Flowering phenology differs among wet and dry sub-alpine meadows in southwestern China

The effect of floral traits, floral rewards and plant water availability on plant-pollinator interactions are well-documented; however, empirical evidence of their impact on flowering phenology in high-elevation meadows remains scarce. In this study, we assessed three levels of flowering phenology, i.e. population-, individual- and flower-level (floral longevity), in two nearby but contrasting (wet versus dry) sub-alpine meadows on Yulong Snow Mountain, southwestern China. We also measured a series of floral traits (pollen number, ovule number, and the ratio of pollen to ovule number per flower, i.e. pollen:ovule ratio [P/O]) and floral rewards (nectar availability and pollen presentation) as plausible additional sources of variation for each phenological level. Floral longevity in the wet meadow was significantly longer than that for the dry meadow, whereas population- and individual-flowering duration were significantly shorter. Our results showed a significant positive relationship between flowering phenology with pollen number and P/O per flower; there was no relationship with ovule number per flower. Further, we found a significant effect of flowering phenology on nectar availability and pollen presentation. Our findings suggest that shorter floral longevity in dry habitats compared to wet might be due to water-dependent maintenance costs of flowers, where the population- and individual-level flowering phenology may be less affected by habitats. Our study shows how different levels of flowering phenology underscore the plausible effects of contrasting habitats on reproductive success.

Patterns of high-flying insect abundance are shaped by landscape type and abiotic conditions

Insects are of increasing conservation concern as a severe decline of both biomass and biodiversity have been reported. At the same time, data on where and when they occur in the airspace is still sparse, and we currently do not know whether their density is linked to the type of landscape above which they occur. Here, we combined data of high-flying insect abundance from six locations across Switzerland representing rural, urban and mountainous landscapes, which was recorded using vertical-looking radar devices. We analysed the abundance of high-flying insects in relation to meteorological factors, daytime, and type of landscape. Air pressure was positively related to insect abundance, wind speed showed an optimum, and temperature and wind direction did not show a clear relationship. Mountainous landscapes showed a higher insect abundance than the other two landscape types. Insect abundance increased in the morning, decreased in the afternoon, had a peak after sunset, and then declined again, though the extent of this general pattern slightly differed between landscape types. We conclude that the abundance of high-flying insects is not only related to abiotic parameters, but also to the type of landscapes and its characteristics, which, on a long-term, should be taken into account for when designing conservation measures for insects.

Responses in honeybee and bumblebee activity to changes in weather conditions

Insect pollination, and in particular pollination by bees, is a highly valued ecosystem service that ensures plant reproduction and the production of high-quality crops. Bee activity is known to be influenced by the weather, and as the global climate continues to change, the flying frequency and foraging behaviour of bees may also change. To maximise the benefits of pollination in a changing world, we must first understand how current weather conditions influence the activity of different bee species. This is of particular interest in a country such as Ireland where inclement weather conditions are nominally sub-optimal for foraging. We observed honeybee (Apis mellifera) and buff-tailed bumblebee (Bombus terrestris) activity across a variety of weather conditions at seven apple orchards to determine how four weather variables (temperature, relative humidity, solar radiation, wind) influenced the flight activity of each species. Each orchard contained three honeybee and three bumblebee colonies, and so we were able to observe a colony of each species concurrently in the same weather conditions. Overall, honeybees were more sensitive to changes in weather than bumblebees and could be more predisposed to future changes in within-day weather conditions. Our results indicate bumblebees could compensate for low honeybee activity in inclement conditions, which supports the theory that pollinator diversity provides resilience. This may be particularly important in management of pollinators in crops that flower in the spring when weather is more variable, and to allow varied responses to global climate change.

Flower-Visiting Insect Assemblages on Fall-Blooming Native California Sage Scrub Shrubs

Pollinator studies in the endangered California sage scrub ecosystem have focused on spring insect assemblages, when most plant species bloom. Consequently, the insect assemblages using common fall-blooming sage scrub shrubs Lepidospartum squamatum, Ericameria pinifolia, and Baccharis pilularis remain undescribed. Our study aimed to: (1) document flower-visiting insect assemblages on fall-blooming shrubs, (2) assess the efficacy of three sampling techniques in inventorying insect assemblages, and (3) explore, using DNA metabarcoding, which plants are utilized and the extent to which surrounding suburban habitats’ plants are also used. While elevated sampling is required to inventory flower-visiting insects, we describe a diverse assemblage consisting of 123 species. Insect assemblages differed between L. squamatum and B. pilularis, as well as, E. pinifolia and B. pilularis, but not between L. squamatum and E. pinifolia. Direct sampling approaches (netting and photo documentation) collected 115 species not collected by passive malaise traps, highlighting that active observations are required to describe flower-visiting insect assemblages. Sequencing the ITS2 region of pollen from abundant visitors revealed that a majority of pollen is from the sage scrub ecosystem, highlighting its value. Our results indicate that the presence of fall-blooming shrubs may be critical for maintaining diverse sage scrub insect and pollinator assemblages.

The Early Season Community of Flower-Visiting Arthropods in a High-Altitude Alpine Environment

In mountain ecosystems, climate change can cause spatiotemporal shifts, impacting the composition of communities and altering fundamental biotic interactions, such as those involving flower-visiting arthropods. On of the main problems in assessing the effects of climate change on arthropods in these environments is the lack of baseline data. In particular, the arthropod communities on early flowering high-altitude plants are poorly investigated, although the early season is a critical moment for possible mismatches. In this study, we characterised the flower-visiting arthropod community on the early flowering high-altitude Alpine plant, Androsace brevis (Primulaceae). In addition, we tested the effect of abiotic factors (temperature and wind speed) and other variables (time, i.e., hour of the day, and number of flowers per plant) on the occurrence, abundance, and diversity of this community. A. brevis is a vulnerable endemic species growing in the Central Alps above 2000 m asl and flowering for a very short period immediately after snowmelt, thus representing a possible focal plant for arthropods in this particular moment of the season. Diptera and Hymenoptera were the main flower visitors, and three major features of the community emerged: an evident predominance of anthomyiid flies among Diptera, a rare presence of bees, and a relevant share of parasitoid wasps. Temperature and time (hour of the day), but not wind speed and number of flowers per plant, affected the flower visitors' activity. Our study contributes to (1) defining the composition of high-altitude Alpine flower-visiting arthropod communities in the early season, (2) establishing how these communities are affected by environmental variables, and (3) setting the stage for future evaluation of climate change effects on flower-visiting arthropods in high-altitude environments in the early season.