Carlos H. Vergara

Non-bee insects are important contributors to global crop pollination

Significance Many of the world’s crops are pollinated by insects, and bees are often assumed to be the most important pollinators. To our knowledge, our study is the first quantitative evaluation of the relative contribution of non-bee pollinators to global pollinator-dependent crops. Across 39 studies we show that insects other than bees are efficient pollinators providing 39% of visits to crop flowers. A shift in perspective from a bee-only focus is needed for assessments of crop pollinator biodiversity and the economic value of pollination. These studies should also consider the services provided by other types of insects, such as flies, wasps, beetles, and butterflies—important pollinators that are currently overlooked. Wild and managed bees are well documented as effective pollinators of global crops of economic importance. However, the contributions by pollinators other than bees have been little explored despite their potential to contribute to crop production and stability in the face of environmental change. Non-bee pollinators include flies, beetles, moths, butterflies, wasps, ants, birds, and bats, among others. Here we focus on non-bee insects and synthesize 39 field studies from five continents that directly measured the crop pollination services provided by non-bees, honey bees, and other bees to compare the relative contributions of these taxa. Non-bees performed 25–50% of the total number of flower visits. Although non-bees were less effective pollinators than bees per flower visit, they made more visits; thus these two factors compensated for each other, resulting in pollination services rendered by non-bees that were similar to those provided by bees. In the subset of studies that measured fruit set, fruit set increased with non-bee insect visits independently of bee visitation rates, indicating that non-bee insects provide a unique benefit that is not provided by bees. We also show that non-bee insects are not as reliant as bees on the presence of remnant natural or seminatural habitat in the surrounding landscape. These results strongly suggest that non-bee insect pollinators play a significant role in global crop production and respond differently than bees to landscape structure, probably making their crop pollination services more robust to changes in land use. Non-bee insects provide a valuable service and provide potential insurance against bee population declines.

Sporadic food competition with the African honey bee: projected impact on neotropical social bees

Bee colonies in lowland forest in Panama were monitored for pollen and nectar harvest, pollen species utilization and nectar quality and quantity per returning forager. Despite sharing most pollen resources and nectar of the same quality with 20 introduced colonies of the African honey bee (Apis mellifera), native stingless bees of 12 species were largely unaffected by its activity. Pollen and nectar harvested by the honey bees were 10-200 times that pro- cured by 17 stingless bee colonies. This discrepancy in total harvest and general lack of com- petitive effect is explained by a honey bee foraging area over 10 times that of the native bees, and apparent foraging shifts to escape competition with honey bees, thus reduced potential overlap in foraging sites. Seven cases of direct resource competition for pollen or nectar were documented, out of 31 tests. Rare periods of intensive harvest were diminished by competing African honey bees. Such harvest peaks lasted for only a few hours in 13 days of observation. Despite average dura- tion of 4%o foraging time for each species, peaks included as much as 51% total harvest. Calcu- lations based upon colony populations, food stores and flight range show that if African honey bees persist at a density of 1 colony per km2, colonies of some stingless bee species may dis- appear after 10 years. Their chances of escaping food competition by taxonomic specialization on flowers seem slight.

Trait matching of flower visitors and crops predicts fruit set better than trait diversity

Understanding the relationships between trait diversity, species diversity and ecosystem functioning is essential for sustainable management. For functions comprising two trophic levels, trait matching between interacting partners should also drive functioning. However, the predictive ability of trait diversity and matching is unclear for most functions, particularly for crop pollination, where interacting partners did not necessarily co-evolve. World-wide, we collected data on traits of flower visitors and crops, visitation rates to crop flowers per insect species and fruit set in 469 fields of 33 crop systems. Through hierarchical mixed-effects models, we tested whether flower visitor trait diversity and/or trait matching between flower visitors and crops improve the prediction of crop fruit set (functioning) beyond flower visitor species diversity and abundance. Flower visitor trait diversity was positively related to fruit set, but surprisingly did not explain more variation than flower visitor species diversity. The best prediction of fruit set was obtained by matching traits of flower visitors (body size and mouthpart length) and crops (nectar accessibility of flowers) in addition to flower visitor abundance, species richness and species evenness. Fruit set increased with species richness, and more so in assemblages with high evenness, indicating that additional species of flower visitors contribute more to crop pollination when species abundances are similar.Synthesis and applications. Despite contrasting floral traits for crops world-wide, only the abundance of a few pollinator species is commonly managed for greater yield. Our results suggest that the identification and enhancement of pollinator species with traits matching those of the focal crop, as well as the enhancement of pollinator richness and evenness, will increase crop yield beyond current practices. Furthermore, we show that field practitioners can predict and manage agroecosystems for pollination services based on knowledge of just a few traits that are known for a wide range of flower visitor species. Despite contrasting floral traits for crops world-wide, only the abundance of a few pollinator species is commonly managed for greater yield. Our results suggest that the identification and enhancement of pollinator species with traits matching those of the focal crop, as well as the enhancement of pollinator richness and evenness, will increase crop yield beyond current practices. Furthermore, we show that field practitioners can predict and manage agroecosystems for pollination services based on knowledge of just a few traits that are known for a wide range of flower visitor species. Editors Choice

Potential negative effects of exotic honey bees on the diversity of native pollinators and yield of highland coffee plantations

1 The honey bee Apis mellifera is native to Eurasia and Africa, although it is commonly introduced into crop fields of different parts of the world because of the assumption that it improves yield. This bee is, however, a poor pollinator of several crops compared with native insects. Indeed, honey bees can displace native pollinators and reduce their diversity. The present study evaluated the potential impacts of A. mellifera on the diversity of native pollinators of highland coffee (Coffea arabica) and its putative consequences for coffee production at the state of Veracruz, Mexico. 2 The abundance of A. mellifera and diversity of native pollinators were assessed during blooming at 12 shade coffee plantations and pollination experiments were conducted to determine the impacts of pollinators on coffee fruit production. Regression analyses were used to assess whether the abundance of honey bees was related to native pollinator diversity, and whether fruit production was influenced by both the diversity of pollinators and the abundance of A. mellifera. 3 Native pollinator diversity decreased as the number of honey bees increased. Furthermore, although coffee fruit production was positively related to the diversity of native pollinators, an increasing abundance of A. mellifera was correlated with a decrease in fruit production. 4 Highland shade coffee plantations are considered as reservoirs of the Mexican insect fauna. Thus, native pollinator diversity could be better preserved if beekeepers reduced the number of managed hives that they brought into plantations. This may also help to increase coffee yield by decreasing the putative negative effects of A. mellifera on native pollinators.

Large scale patterns of abundance and distribution of parasites in Mexican bumblebees

Bumblebees are highly valued for their pollination services in natural ecosystems as well as for agricultural crops. These precious pollinators are known to be declining worldwide, and one major factor contributing to this decline are infections by parasites. Knowledge about parasites in wild bumblebee populations is thus of paramount importance for conservation purposes. We here report the geographical distribution of Crithidia and Nosema, two common parasites of bumblebees, in a yet poorly investigated country: Mexico. Based on sequence divergence of the Cytochrome b and Glycosomal glyceraldehyde phosphate deshydrogenase (gGPDAH) genes, we discovered the presence of a new Crithidia species, which is mainly distributed in the southern half of the country. It is placed by Bayesian inference as a sister species to C. bombi. We suggest the name Crithidia mexicana for this newly discovered organism. A population of C. expoeki was encountered concentrated on the flanks of the dormant volcanic mountain, Iztaccihuatl, and microsatellite data showed evidence of a bottleneck in this population. This study is the first to provide a large-scale insight into the health status of endemic bumblebees in Mexico, based on a large sample size (n=3,285 bees examined) over a variety of host species and habitats.

A New Species of Caupolicana s.str. from the Tehuacán-Cuicatlán Valley, Mexico, and a Key to North American Species of the Subgenus (Hymenoptera: Colletidae)

Abstract Caupolicana (Caupolicana) evansi, a new species similar to C. yarrowi (Cresson), is described from the Valley of Zapotitlán de las Salinas, in the Tehuacán Desert and from the nearby Cuicatlán Valley of Mexico. A key to the six North American species of Caupolicana s.str. is included.

Butterfly Conservation within Cities: A Landscape Scale Approach Integrating Natural Habitats and Abandoned Fields in Central Mexico:

Growing urbanization and the expansion of the agricultural frontier in tropical ecosystems have generated patchy landscapes composed of remnants of natural habitats and abandoned fields. This scenario offers an opportunity to develop urban reserves in order to preserve local fauna in expanding cities. We propose that if native animals are able to use these two habitat types, reserves composed of a mixture of natural habitats and abandoned fields would contain more diversity than reserves composed only of natural habitats. However, to be useful for conservation, these reserves must harbor specialized organisms that depend on natural habitats. To test this proposal, we focused on diurnal butterflies inhabiting an urban reserve located within the city of Puebla (Mexico), which contains relics of oak forests and abandoned fields. Butterfly assemblages were sampled and compared in the different habitat types of the reserve. The data were then pooled and analyzed for the reserve as a whole. These analyses discriminated between habitat generalist and forest specialist butterflies. Our results indicated that the different habitat types of the reserve harbor different forest specialist butterflies, which in turn enhanced the diversity of forest-dwelling butterflies at the landscape scale. This suggests that the inclusion of abandoned fields together with natural habitats in the design of urban protected areas could help to preserve at least part of the regional biodiversity.