Nest architecture, life cycle, and natural enemies of the neotropical leafcutting bee Megachile (Moureapis) maculata (Hymenoptera: Megachilidae) in a montane forest

Abstract

-Studies on the nesting biology of cavity nesting hymenoptera (bees and wasps) have stimulated many questions related to the behavior, life cycle, trophic niche, and sex ratio to better understanding of the life history of insects. Leafcutting bees are common insects, and many are important and efficient pollinators of crops and other plants. We studied the nesting biology of Megachile (Moureapis ) maculata in a montane semi-deciduous forest in Brazil using trap nests in order to improve the knowledge of aspects of the natural history of this important pollinator group. During 27 months, 87 nests were collected with an average of seven brood cells per nest. Most of the nests were in cavities of 0.9 cm in diameter (77%), and the number of brood cells ranged from 1 to 11. Absence of seasonality in nesting behavior suggests a multivoltine species. The total mortality rate was 26%, with the cuckoo bee Coelyoxis (Acrocoelioxys ) sp. being the main natural enemy attacking 15% of brood cells. The sex ratio is clearly male-biased (1:0.42). Females and their brood cells were larger than males and their brood cells, which may suggest an imbalance in the energetic cost of each sex. The success of this bee species in colonizing trap nests makes it an interesting potential opportunity to use this species for pollination of cultivated Asteraceae plant species, like sunflower.Atlantic forest / sex ratio / solitary bees / trap nests INTRODUCTIONThe genus Megachile Latreille, 1802 (Megachilidae) is large, with 1524 species described, of which 147 have been recorded from Brazil (Ascher and Pickering 2015). Species of megachilid bees use several nesting substrates. Some species dig nests in the soil, but most are specialists in using pre-existing cavities in the ground, among rocks or in pithy stems and galls (Eickwort et al. 1981). Pre-existing cavities are also found in dead wood, such as old galleries of wood-dwelling beetles, which are important nest spaces in forest ecosystems (Zuo et al. 2016).Materials used for nesting construction are quite diverse, including sand, mud, resins, plant trichomes, petals, and leaf pieces. The behavior of nesting in cavities probably evolved repeatedly in ancestral species that nested in the soil (Eickwort et al. 1981) and may be more common than once supposed. Females, particularly of the genus Megachile , use their mandibles to cut pieces of leaves used to build their brood cells. This remarkable behavior, of using pieces of leaves to build the brood cells, is unique among bees.

Foraging preferences of leafcutter bees in three contrasting geographical zones

“…The bees cut and collect circular to elliptical leaf pieces (Figure ) and line the brood cells with a roll of layered discs. A single brood cell may contain 50–100 leaf discs; depending on the size of the cavity, an aboveground nest may contain 1–11 brood cells (MacIvor, ; Sabino & Antonini, ), while the subterranean nests contain a single brood cell (Williams et al., ). The leaf discs are also used to partition the brood cells.…”

Notes on a nest of Megachile (Moureapis) apicipennis Schrottky (Megachilidae) constructed in an abandoned gallery of Xylocopa Frontalis (Olivier) (Apidae)

“…Despite its high richness and wide distribution, only a few studies have reported the nesting biology of species from this subgenus (Ihering, 1904;Laroca, 1991;Teixeira et al, 2011;Cardoso & Silveira, 2012;Sabino & Antonini, 2017). Here we provide notes on a nest of Megachile (Moureapis) apicipennis Schrottky (Megachilidae) built in an abandoned nest of Xylocopa frontalis (Olivier) (Apidae).…”

“…(Laroca, 1991;Teixeira et al, 2011;Cardoso & Silveira, 2012;Sabino & Antonini, 2017) except for Ihering (1904). According to this author, the brood cell walls of a M. apicipennis nest were constructed with mud rather than with pieces of leaves.…”

“…The use of leaves of leguminous species (Fabaceae) to construct brood cells was also recorded in another M. (Moureapis) species. Sabino and Antonini (2017) identified leaves of Senna pendula (Willd.) H.S.Irwin and Barneby and Dalbergia miscolobium Benth.…”

“…The only host record for Brachymeria paraguayensis was provided by Noyes (2003) for an unidentified Megachile species. The generalist parasitoid Melittobia australica has been recorded as a natural enemy of several bee species, including five in the genus Megachile, as M. Maculata (Sabino & Antonini, 2017), as well as flies (Calliphoridae, Sarcophagidae) and species of Crabronidae, Formicidae, Pompilidae, Sphecidae, and Vespidae (Noyes, 2003). Species of Coelioxys Latreille and Melittobia Westwood were also reported parasitizing brood cells of other M. (Moureapis) species (Teixeira et al, 2011;Cardoso & Silveira, 2012;Sabino & Antonini, 2017).…”