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Nesting biology of the solitary digger bee Habropoda depressa (Hymenoptera: Anthophoridae) in urban and island environments.

1998; Kansas (Central States) Entomological Society; Volume: 71; Issue: 2 Linguagem: Inglês

1937-2353

Barthell Jf, Bromberger Dm, Daly Hv, Thorp Rw,

Plant Parasitism and Resistance

The nesting biology of Habropoda depressa Fowler is described for urban (University of California at Berkeley) and island (Santa Cruz Island) populations in the state of California (USA). This protandrous species is common in the California foothills where adults are active from late February through early June. Larvae do not spin cocoons and pu pate to overwinter as adults by November. A portion of the population appears to delay de velopment since prepupae were found in nest excavations early in the nesting season. Brood cells were parasitized mostly by two dipterans: bombyliid flies and an anthomyiid species, Leucophora fusca Huckett (found only on SCI). Unlike its congeners which nest in sandy soils, H. depressa nests in hard-packed soils, including clay. During the nesting season, fe males spend evenings outside burrows, roosting on nearby vegetation before returning to their nest the following morning. At the urban locale, female bees subsist almost entirely upon ex otic and horticultural plant varieties while the majority of host plant collection records at Santa Cruz Island were from native species. On average, nests made by bees at V^IB were significantly shorter than those constructed at SCI, although the average number of cells per nest was greater. These foraging and nest architectural differences may reflect either varia tion among populations or adaptations to urbanization effects of the last century. Habropoda (formerly Emphoropsis) is a solitary, ground-nesting, bee genus of nine North American species, most of which occur in the western USA (Brooks, 1988). To remain consistent with recent biological literature and taxonomic treat ments (e.g., Michener et al., 1994), we refer here to this genus as a member of the Anthophoridae although we recognize that this family is a subgroup among the monophyletic Apidae (Roig-Alsina and Michener, 1993). A compilation of speci men records from the University of California at Berkeley and Davis Insect Muse ums indicate Habropoda depressa Fowler is common in the foothill regions of Cal ifornia (Fig. 1). Supplemental specimens were examined at the Snow Entomological Museum (University of Kansas Natural History Museum) and confirm distribution patterns in California as well as indicating records in northwestern Arizona (includ ing localities near Kingman and Sedona). One of us (R.W.T.) also observed a spec imen in southern Oregon. Collection dates (from UC Berkeley and UC Davis col lections) indicate that populations are protandrous, with males reaching their peak numbers in the latter half of March while females are most commonly found nest ing in late March and April (Fig. 2). Males are known to exhibit size and behavioral dimorphism during the location of mates (Barthell and Daly, 1995). Until now, how ever, little has been reported on the nesting biology of this species. Habropoda depressa was described from specimens collected at the University of California at Berkeley campus and Santa Catalina Island (Fowler, 1899). The UC 1 Department of Biology, University of Central Oklahoma, Edmond, Oklahoma 73034. 2 Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720. 3 Department of Entomology, University of California, Davis, California 95616. Accepted for publication 29 July 1998. This content downloaded from 207.46.13.114 on Thu, 26 May 2016 06:04:17 UTC All use subject to http://about.jstor.org/terms VOLUME 71, ISSUE 2 117 Fig. 1. Habropoda depressa collection locales in California (based upon museum specimens). Berkeley specimens originated from the original university botanical gardens in the north-central portion of the campus. We discovered a nesting population of this spe cies in the same region of campus which now is developed with buildings and land scaping. Here we report on aspects of this species' nesting biology by comparing the urban UC Berkeley population with a population from a less disturbed island locale (Santa Cruz Island), supplemented with host plant records from other California lo cales. Materials and Methods study locales: Most of the research was conducted on the University of Cali fornia at Berkeley campus (UCB). The main campus covers about a one km2 area at the base of the East Bay Hills in Berkeley (California, USA). Established in 1868, the campus was still a relatively undeveloped area when Habropoda depressa was described from there nearly three decades later by Fowler (1899). Specimens used to describe the species from UC Berkeley were collected near the old campus botan ical garden, which abuts a partially wooded hillside known as Observatory Hill (Fig. 3a). The three nesting sites examined during the current study are located along about a 500 m segment of hillside (running E to W) which intersects this hill. Nearly 100 This content downloaded from 207.46.13.114 on Thu, 26 May 2016 06:04:17 UTC All use subject to http://about.jstor.org/terms 118 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY J-l J-ll F-l F-ll M-l M-ll A-l A-ll M-l M-ll J-l J-ll J-l J-ll Time Intervals (Biweekly) Fig. 2. Phenology of male and female Habropoda depressa in California from January to July based upon museum collections (bars represent proportion of entire collection per 2-week period). years of campus development produced a considerable increase in the density of buildings on the main campus. Indeed, only ruins remain of the original observatory building (after which Observatory Hill is named), the botanical gardens are now lo cated E of the main campus, and the campus itself extends a block further S to Ban croft Avenue (Fig. 3b). Santa Cruz Island (SCI) is located 31 km off the coast from Ventura in southern California. This 25,000 ha island is the largest of the eight Channel Islands and is located about 185 km NW of Santa Catalina Island, another locality from which a H depressa specimen was described by Fowler (1899). SCI contains undisturbed landscape relative to UCB with about 74% of all vascular plants on the island being native (Junak et al., 1995). The island was occupied by a viticultural community dur ing the mid to late 1800's and, subsequently, a cattle ranch. In 1965 the University of California began managing research projects on the island and in 1987 The Na ture Conservancy began stewardship of the western 90% of the island. The National Park Service is now cooperating in the management of the island. The three nesting sites used in the study were along about a 500 m section of Prisoner's Stream, about 1 km N of The Nature Conservancy headquarters. Host plant records made at UCB and SCI were supplemented by regular collec tions made at three California locales: Hastings Natural History Reservation (HNR), Mount Diablo State Park (MDP) and San Joaquin Experimental Range (SJR). HNR is situated 42 km SE of Carmel in the Santa Lucia foothills of Monterey Co. and is part of the University of California Natural Reserve System, managed through the Museum of Vertebrate Zoology (UC Berkeley). MDP is near Danville and managed through the state of California while SJR is operated by the California State Uni versity at Fresno and the U.S. Forest Service. The first two locales are coastal foothill regions, the third is situated among the Sierra Nevada foothills. Each of these locales is part of an ongoing project designed to characterize biodiversity of bees and their floral resource uses among several sites in California (Thorp et al., 1992). observations and excavations: Behavioral notes were taken for both male and female H. depressa, mostly at UCB nesting sites. Mating behavior was observed un This content downloaded from 207.46.13.114 on Thu, 26 May 2016 06:04:17 UTC All use subject to http://about.jstor.org/terms VOLUME 71, ISSUE 2 119 1^1 1^1 b^ ' -^?^ 1?^^ bk^^j b^kJ ES ^5 (^ 'observatory * ^UhH W (remains) ^?*) |^| M ^ fl? i?? * * min w *? ?mi t Eucalyptus Grove