Leaf foraging sources of leafcutter bees in a tropical environment: implications for conservation

Apidologie, Feb 2017

Leafcutter bees collect leaf discs to encase brood cells. However, our understanding of their use of plants as nesting resources, which is critical for their conservation, is poor. We followed plants and observed bees cutting leaves to understand the leaf and plant traits of the leaf forage plants of Megachile spp. We studied whether the leaf size explains the cut size and the number of cuts in the leaves. The bees collected leaves from 59 species, 49 genera and 25 families of plants of various habits. Plant habit, leaf morphotype and leaf size did not influence leaf choice by the bees. Of the plants surveyed, 45.22% had the distinguishable cutting marks. About 63% and 98% of the plants the bees used are native to the region and to the tropical southern hemisphere, respectively. Bees selected leaves over an extreme size range, and the leaf size predicted the number of cuts on a leaf. Comparing our results with other studies, we conclude that the leafcutter bees’ selection of plants is adapted to the local environment.

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Leaf foraging sources of leafcutter bees in a tropical environment: implications for conservation

Apidologie Leaf foraging sources of leafcutter bees in a tropical environment: implications for conservation S. KAMBLİ 1 2 M. S. AISWARYA 0 K. MANOJ 2 VARMA 2 G. ASHA 2 T. P. RAJESH 2 Palatty Allesh SINU 2 3 0 Department of Biology, Indian Institute of Science Education and Research (IISER) , Mohali, Punjab , India 1 Department of Ecology and Environment, Pondicherry University , Pondicherry , India 2 Department of Animal Science, Central University of Kerala , Padannakad, PO 671314, Kerala , India 3 Department of Ecology and Evolutionary Biology, University of Arizona , Tucson, AZ 85721 , USA - Leafcutter bees collect leaf discs to encase brood cells. However, our understanding of their use of plants as nesting resources, which is critical for their conservation, is poor. We followed plants and observed bees cutting leaves to understand the leaf and plant traits of the leaf forage plants of Megachile spp. We studied whether the leaf size explains the cut size and the number of cuts in the leaves. The bees collected leaves from 59 species, 49 genera and 25 families of plants of various habits. Plant habit, leaf morphotype and leaf size did not influence leaf choice by the bees. Of the plants surveyed, 45.22% had the distinguishable cutting marks. About 63% and 98% of the plants the bees used are native to the region and to the tropical southern hemisphere, respectively. Bees selected leaves over an extreme size range, and the leaf size predicted the number of cuts on a leaf. Comparing our results with other studies, we conclude that the leafcutter bees' selection of plants is adapted to the local environment. 1. INTRODUCTION Bees, evolved from sphecoid wasps (Cardinal and Danforth 2013; Grimaldi 1999) , have retained their ancestors’ provisioning habit in nests (Radchenko and Pesenko 1996). However, they use plant matter, such as a blended pollen and nectar mixture (Michener 1964; Cane et al. 2011) , rather than their ancestors’ likely choice of animal matter (Evans 1971) as food for their developing larvae. They have also evolved the habit of lining the brood cells (Michener 1964) . Ancestral sphecoid wasps nested in burrows in the soil and stored the larvae (the provision of the brood) there for many days to weeks in unlined brood cells (Kaltenpoth et al. 2005) . Being hydrophilic in nature, the provision of bee hives is susceptible to early spoilage, particularly from infectious fungal molds (Müller et al. 1996; Messer 1985) . Larvae are also vulnerable to predation and parasitism (Eltz et al. 2015; Krunić et al. 2005) , so bees construct lined brood cells in the burrows in pre-existing cavities below and above ground to reduce predation risk (Eltz et al. 2015; Cane et al. 1983; Messer 1985) . Most bees use a glandular secretion from Dufour’s gland to line the brood cell (Williams et al. 1986; Hefetz 1987; Mitra 2013) , but some species of bees have evolved the habit of using foreign materials, predominantly plant derivatives and soil particles, as their lining (MacIvor 2016; Litman et al. 2011; Cane et al. 1983; Messer 1985) . Common examples of such species are the resinbees and the leafcutter bees belonging to the family Megachilidae. While the former collects plant resins to line cells, the latter collects whole leaves or leaf cuttings to line the brood cells (Wedmann et al. 2009; Litman et al. 2011; MacIvor 2016) . The family Megachilidae has ca. 3900 described species reported from all over the world, with 1478 of these species in the genus Megachile (Michener 2007) . Some of these bees are the most important managed wild pollinators of several c r o p p l a n t s , e s p e c i a l l y t h e m a n a g e d M. rotundata in North America (Pitts-Singer and Cane 2011; Bohart 1972; Kuriakose et al. 2009) . Although we have some information on the nest biology of Megachile bees (Fischer 1951; Butler 1965; Strickler et al. 1996; MacIvor 2016) , the information is sparse for such important specialist pollinators, and includes almost no information from the tropics. However, it is very likely that the abundance of the leaf plants is also an important factor in explaining the geographical distribution and local abundance of these bees. Therefore, knowledge about what the bees collect for their brood cell linings has direct implication in the conservation of leafcutter bees. In this paper, we report the leaf plants of leafcutter bees of peninsular India in a tropical village habitat. We studied whether leafcutter bees favored plants with particular growth habits or with particular leaf morphologies. We further studied whether the size of leaf cuts and number of cuts per leaf varied with the size of the leaves. Since the study took place in a village habitat, we studied what percent of the leaf plants were native to the region. MATERIALS AND METHODS 2.1. Study site and sampling The study was carried out in the North Malabar region of Kerala State in Peninsular India. The ob (...truncated)


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Sneha S. Kambli̇, M. S. Aiswarya, K. Manoj, Sangeetha Varma, G. Asha, T. P. Rajesh, Palatty Allesh Sinu. Leaf foraging sources of leafcutter bees in a tropical environment: implications for conservation, Apidologie, 2017, pp. 473-482, Volume 48, Issue 4, DOI: 10.1007/s13592-016-0490-2