Field experiments with the pollinator species, Osmia lignaria propinqua Cresson, in apple orchards: I, 1975 studies (Hymenoptera: Megachildiae)

A population of Osmia lignaria propinqua Cresson bees was mass-released into an isolated apple (Malus sylvestris Mill.) orchard supplied with numerous nest shelters to determine if release techniques affect dispersal patterns of bee populations. Results obtained demonstrate that mass-released bees disperse much more readily than populations emerged from natal nests. These data also suggest that increased dispersal patterns expressed by mass-released O. I. propinqua populations can at least be partially neutralized by increasing the numbers of nest shelters distributed over a larger geographic area within orchard environments. This accommodation increased the proportion of re leased bees that established nests in shelters supplied, thus resulting in a net increase of population size. Osmia lignaria propinqua Cresson is a native bee species that has recently been shown to be an effective pollinator of orchard crops (Torchio, 1976, 1979; Kuhn and Ambrose, 1984). Subsequent studies (Torchio, 1981a, b, 1982a, b, c) have focused on developing proper management practices for large-sized populations released into commercial orchard environments. Results of those studies have demonstrated that: O. I. propinqua bees express predictive behavioral traits; man agement practices can be designed to accommodate these behavioral expressions once recognized; and, each of these accommodations can result in an increased rate of nesting success by this bee species. These focused studies have, together, demonstrated that the nesting success of Osmia bees is tied directly to dispersal patterns of released populations. Therefore, successful management practices act to reduce rapid dispersal by prenesting bees which, in turn, increases the probability for larger numbers of female bees to establish nests within orchard environments. The resultant increase in numbers of nesting female bees also assures a higher rate of nesting success by that managed bee population, thus increasing the probability for maximizing pollination of the crop. Two particular studies (Torchio, 1982c, 1984) have clearly demonstrated that methods employed in releasing bees, types of nest materials used, and their place ment design each have a major impact on the rate of bee dispersal and, conse quently, nesting success. Those same studies further demonstrate that when more than one influencing factor affecting bee dispersal is properly managed, the re sultant rate of nesting success by that population is compounded. To better understand how these influencing factors interact, an experiment was designed wherein a population of bees was mass-released (increased probability for rapid dispersal) in an orchard supplied with additional nest materials distrib Accepted for publication 9 February 1984. This content downloaded from 207.46. 13.28 on Tue, 30 Aug 2016 04:53:45 UTC All use subject to http://about.jstor. org/terms 690 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY uted over a large geographic area (increased probability of attracting larger num bers of dispersing bees to establish nests in materials supplied). The results of that study are reported herein. Methods and Materials The Osmia bees used in this study were derived from nest trap materials placed in local apple orchards during the previous year. In September 1977, nests were dissected and cocoons were inserted individually into clear, #000, gelatin capsules. These filled capsules were placed in a constant 3? C temperature cabinet on 1 October and then transferred to a 27? C incubation cabinet during the last week of April 1978. During the 4-day incubation period, capsules were individually checked every 3 hours and those with emerged adults were returned to the 3? C temperature cabinet. After incubation was completed, individuals were de-en capsulated in the 3? C temperature cabinet and placed into emergence boxes (Tor chio, 1982a) where they remained until transferred to the orchard for release on 2 May. The same 2.63-hectare orchard used for experimentation the previous year (Torchio, 1984) was also used in 1978. Sixty-four plywood, military footlockers (each 81.3 cm x 43.2 cm x 30.5 cm) were placed as nest shelters, and each was attached to metal fence posts (Torchio, 1982c) to face SE. Each nest shelter was positioned adjacent to a tree within a 13-row diameter that formed an encirclement of nest shelters surrounding the central point where bees were mass-released. To measure dispersal rates, it was necessary to position nest shelters equidistant from each other and at various distances from the release site. This was accom plished by establishing three circles of nest shelters with each having a particular radial distance from the release site: The inner encirclement was composed of 16 shelters and each was positioned 18.5 meters from the release site; sixteen ad ditional shelters were used to establish a middle circle, 30.8 radial meters from the release site; and the outermost circle was composed of 32 nest shelters, each positioned 34 meters from the release site. One additional shelter was then placed near the release site to house a Belfort? hygrothermograph (continuous recorder) that remained operational throughout the flight period of bees (2-23 May). Two nest materials (milk cartons and drilled laminates) were used in this study. The milk carton units were identical to those tested previously (Torchio, 1982c) with the exception that paper soda straws were painted black. These straws were darkened when, during the previous year's observations, it was discovered that light (from a flashlight) entering one unpainted straw diffused through it to lighten adjacent straws, thus decreasing their attractivity to bees searching for nest holes. The drilled laminates were of 2 sizes with the shorter unit measuring 14.5 cm3 and containing 52 drilled holes in which each had a paper soda straw (14 cm long x 7 mm wide) inserted. The longer laminate nest unit was 29 cm wide x 14.5 cm2 and contained 105 drilled holes, each with an inserted paper soda straw of the same dimensions as those in the shorter laminate units. Two milk carton nest traps were placed in each of the 64 nest shelters. Two short laminate nest traps were placed in each of the 16 shelters nearest the release site (inner circle) and one laminate nest trap was placed in each of the 32 nest shelters furthest from the release site (outer circle). In addition, one long laminate nest trap was placed in each of the 32 nest shelters comprising the inner and This content downloaded from 207.46. 13.28 on Tue, 30 Aug 2016 04:53:45 UTC All use subject to http://about.jstor. org/terms VOLUME 57, NUMBER 4 691 Table 1. Nesting success of O. I. propinqua/nest material/unit area. Dead immatures # # %nest Nest material Area nests cells So 2$ # % utilization Milk cartons Inner circle 50 173 107 30 36 20.8 6.8 Milk cartons Middle circle 86 301 200 60 41 13.6 11.7 Milk cartons Outer circle . 103 35J_ 22j_ J70 _60 Jj^9 _5JS 239 825 528 160 137 16.6 8.1 Short laminates Inner circle 185 588 367 175 46 7.8 11.1 Short laminates Outer circle \9? 645 407 185 J3 JU 117 379 1233 774 360 99 8.0 11.4 Long laminates Inner circle 154 515 329 143 43 8.3 9.2 Middle circle H6 _459 283 L40 _36 _718 _8J 300 974 612 283 79 8.1 8.9 middle circles. Thus, 224 nest traps representing 9632 nest holes were made available for this experiment. The inner circle was supplied with 5 nest units and 255 holes/shelter (4080 total nest holes), whereas the middle and outer circles were supplied with fewer traps/shelter (3 and 4), fewer nest holes/shelter (151 and 150), and fewer total nesting holes (2416 and 3136). All nest traps were placed in the middle of each nest shelter in similar designs.