HORTICULTURAL ENTOMOLOGY Flies (Diptera: Muscidae: Calliphoridae) Are Efficient Pollinators of Allium ampeloprasum L. (Alliaceae) in Field Cages STEPHEN L. CLEMENT,1,2 BARBARA C. HELLIER,1 LESLIE R. ELBERSON,1 1 3 RUSSELL T. STASKA, AND MARC A. EVANS J. Econ. Entomol. 100(1): 131Ð135 (2007) ABSTRACT In conjunction with efforts to identify efÞcient insect pollinators for seed multiplication of cross-pollinated plant species stored and maintained by USDAÐARS Western Regional Plant Introduction Station (WRPIS), experiments were conducted to assess and compare the efÞciency of the house ßy, Musca domestica L. (Diptera: Muscidae), and Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae), and different densities of each ßy species, to pollinate leek, Allium ampe- loprasum L., plant inventory (PI) accessions in Þeld cages for seed yield maximization and high germination. Cages with ßowering plants were exposed to 0 ßies or stocked with 100, 250, and 500 M. domestica or C. vicina pupae per week for 6 (2002) and 7 (2004) wk. Seed yield (weight per cage) increased linearly as ßy densities (C. vicina or M. domestica) increased from 0 to 500 pupae per week, with 500 ßy cages averaging 340.7 g (C. vicina) and 70.5 g (M. domestica) of seed in 2002 (PI 368343) and 615.3 g (PI 168977) and 357.5 g (PI 368343) in 2004 when only the C. vicina was used. For 0, 100, and 250 ßy cages, seed yields averaged between 2.3 and 175.3 g in 2002 and 10.7 and 273.1 g in 2004. Mean 100-seed weights between treatments ranged narrowly between 0.4 and 0.5 g in 2002 and 0.3 and 0.4 g in 2004, and germination rates of seed lots from “ßy cages” were mostly Ն80% in both years. The C. vicina is an efÞcient and cost-effective pollinator ($388.97 for pupae and shipping, compared with $2,400 for honey bee, Apis mellifera L. [Hymenoptera: Apidae], nuclei) for caged leek accessions, with 250 and 500 C. vicina pupae per week required to produce sufÞcient seed (130 g) to Þll an accession storage bag in the WRPIS gene bank. KEY WORDS leek, Calliphora vicina, Musca domestica, germplasm regeneration, insect pollination Regeneration of seed-propagated plant species is one plant species, and a seed lot inventory of Ϸ72,500 of the most important tasks for gene bank curators and accessions) in the U.S. National Plant Germplasm Sys- managers. This activity, which normally involves Þeld tem. A sizeable percentage of WRPIS germplasm is nurseries with multiple plant accessions, is necessary cross-pollinated species, including species in the ge- to replenish seed stocks in cold storage that are low in nus Allium (Alliaceae). Among the 105 species and 978 viability and supply. However, there is a risk of unin- accessions of Allium in WRPIS collections are 204 leek tended hybridization among accessions of allogamous accessions, A. ampeloprasum L. [sometimes classiÞed (outcrossing) entomophilous plant species if acces- as A. porrum (L.)]. Leek is a vegetable belonging to sions are clustered in Þeld nurseries. To prevent in- the onion family and is used as an ingredient in soups sect-meditated cross-pollination between clustered and salads. There are three other horticultural groups accessions in open-Þeld nurseries, gene bank curators in A. ampeloprasum (Kurrat, Great-headed Garlic, and use spatial isolation of accessions or Þeld cages over Pearl Onion), which are mainly cultivated in Europe plants with suitable insect pollinators (Clark et al. and the Middle East, but on a smaller scale than leeks. 1997, Schittenhelm et al. 1997). Leeks are an important crop in Europe. Wild A. am- The USDAÐARS Western Regional Plant Introduc- peloprasum originates from Portugal in the west tion Station (WRPIS), Pullman, WA, is a major gene through the Mediterranean countries to Iran and else- bank for plant collections (358 plant genera, 2,194 where in the Middle East (van der Meer and Hanelt 1990, Brewster 1994). Leeks, which do not normally bulb like onions, are grown from seed. Mention of a trademark or a product does not constitute a guarantee A leek seed stalk can approach 1.2 m in height and or warranty by the USDA and does not imply its approval over other suitable products. is terminated by a single umbel containing hundreds 1 USDAÐARS, Plant Germplasm Introduction and Testing Research of bell-shaped ßowers with light purple petals. These Unit, 59 Johnson, Hall, Washington State University, Pullman, WA protandrous ßowers facilitate out-crossing. However, 99164-6402. protandry only offers a partial barrier to self-pollina- 2 Corresponding author, e-mail: [email protected]. 3 Department of Statistics, Washington State University, Pullman, tion because pollen from ßowers that typically open WA 99164-3144. over 2Ð4 wk can fertilize receptive stigma of more 132 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 100, no. 1 advanced ßowers in the same umbel (McGregor 1976, CA (M. domestica) and Forked Tree Ranch, Porthill, Brewster 1994). This potential for self-pollination ID (C. vicina). Once a week between 8 July and 12 complicates seed regeneration because leeks are sub- August 2002, these vendors express-mailed 5,000Ð15,000 ject to severe inbreeding depression, which can lead pupae of their respective ßy species to Pullman, WA. to severe loss of vigor and reduced survival in seedlings In 2004, only C. vicina pupae were required for this derived from self-pollination (Currah 1986, Brewster study, and 15,000 pupae were purchased from Forked 1994, Silvertand et al. 1995). Therefore, leek acces- Tree Ranch and shipped weekly, 6 July to 16 August. sions must be regenerated without risk of contamina- Caged Field Experiments. The experiments were tion by pollen from neighboring accessions, yet under conducted, 2001Ð2002 and 2003Ð2004, at a major conditions that encourage high rates of cross-pollina- WRPIS seed regeneration site (25 ha) bordering the tion. These requirements can be accomplished by cou- Snake River and near Central Ferry in southeastern pling a suitable insect pollinator with caged plants of Washington (46Њ 40Ј 13Љ N, 117Њ 45Ј 8Љ W). Plots were a leek accession. established using 4-wk-old seedlings grown from The honey bee, ßies in the genera Calliphora, Lu- seed in a glasshouse and transplanted to the Þeld on cilia (Diptera: Calliphoridae), and Eristalis (Diptera: 26 and 27 September 2001 and 15Ð17 October 2003. Syrphidae), and the solitary bee Osmia rufa L. (Hy- The seedlings were transplanted into black plastic menoptera: Megachilidae) have been used to polli- ground cover for weed suppression and watered nate caged onions, A. cepa L. (Moffett 1965; Bohart et with drip irrigation as needed. Nitrogen was applied al. 1970; Free 1970; Schittenhelm et al. 1997; Currah before transplanting at 45 kg ⅐ haϪ1. No pesticides and Ockendon 1983, 1984). Although some of these were applied and weed control was by cultivation investigators found that ßies and honey bees were before transplantation and hand hoeing thereafter. equivalent in their suitability as pollinators for caged A plot (4 by 7 m) consisted of four 6-m-long rows onions (Currah and Ockendon 1983, 1984), others on 0.3-m centers, with each row containing 18Ð20 reported that calliphorid and Eristalis ßies were more evenly spaced transplants for a total of 75Ð80 plants suitable than honey bees for cross-pollinating onions per plot. The spacing between plots was 1.5 m. Each in cages (Bohart et al. 1970, Free 1970). It is well plot was thinned to 53 and 49 bolting plants on 8 May known that onion ßowers are unattractive to the 2002 and 16 June 2004, respectively. In June 2002 and honey bee (Bohart et al. 1970, McGregor 1976, Silva et 2004, before plants ßowered, each plot was covered al. 2003), so it is not surprising that some ßy species with a screen Þeld cage (4 by 7 by 2 m) (Synthetic might be better pollinators for caged onions, as well as Industries, Gainesville, GA) and randomly assigned a other alliums. Schittenhelm et al. (1997) did not rec- ßy density treatment: 100, 250, and 500 M. domestica or ommend the solitary bee O. rufa as a pollinator for C. vicina pupae, and one 0 ßy cage (no pupae added) caged onions because it was repelled by the plants. in 2002; and 0, 100, 250, and 500 C. vicina pupae in 2004. Without published accounts on the efÞciency of These assignments resulted in seven treatment cages different insects for pollinating A. ampeloprasum in per block in 2002 (one leek accession [PI 368343] ϫ cages, but armed with the results of the aforemen- two ßy species ϫ 3 ßy rates ϩ one 0 ßy cage) and eight tioned reports on A. cepa pollination, we chose to treatment cages per block in 2004 (two leek accessions evaluate two ßy species for their efÞciency to pollinate [PI 368343, PI 168977] ϫ one ßy species ϫ 4 ßy rates). leek accessions in cages. In addition, ßy pupae were Each experiment was replicated four times in random- available from commercial suppliers, whereas honey ized complete blocks for a total of 28 and 32 cages in bees, Apis mellifera L. (Hymenoptera: Apidae), were 2002 and 2004, respectively. Cages were secured to the unavailable at the start of this study. ground by using metal stakes and bottom edges along The research objective of this multiyear study was each side were buried in soil. to assess and compare the efÞciency of the house ßy, Fly pupae were placed in cages at the onset of Musca domestica L. (Diptera: Muscidae), and Calli- ßowering and until ßowering was complete. There phora vicina Robineau-Desvoidy (Diptera: Callipho- were six weekly release dates (8 JulyÐ12 August) in ridae), and variable densities of each species, to pol- 2002 and seven (6 JulyÐ16 August) in 2004.