High invasive pollen transfer, yet low deposition on native stigmas in a Carpobrotus-invaded community

Bartomeus I., Bosch J., Vilà M. (2008) High invasive pollen transfer, yet low deposition on native stigmas in a Carpobrotus-invaded community. Annals of Botany. 102: 417-424.
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Doi: 10.1093/aob/mcn109

Resum:

• Background and Aims: Invasive plants are potential agents of disruption in plant-pollinator interactions. They may affect pollinator visitation rates to native plants and modify the plant-pollinator interaction network. However, there is little information about the extent to which invasive pollen is incorporated into the pollination network and about the rates of invasive pollen deposition on the stigmas of native plants. • Methods: The degree of pollinator sharing between the invasive plant Carpobrotus affine acinaciformis and the main co-flowering native plants was tested in a Mediterranean coastal shrubland. Pollen loads were identified from the bodies of the ten most common pollinator species and stigmatic pollen deposition in the five most common native plant species. • Key Results: It was found that pollinators visited Carpobrotus extensively. Seventy-three per cent of pollinator specimens collected on native plants carried Carpobrotus pollen. On average 23% of the pollen on the bodies of pollinators visiting native plants was Carpobrotus. However, most of the pollen found on the body of pollinators belonged to the species on which they were collected. Similarly, most pollen on native plant stigmas was conspecific. Invasive pollen was present on native plant stigmas, but in low quantity. • Conclusions: Carpobrotusis highly integrated in the pollen transport network. However, the plant-pollination network in the invaded community seems to be sufficiently robust to withstand the impacts of the presence of alien pollen on native plant pollination, as shown by the low levels of heterospecific pollen deposition on native stigmas. Several mechanisms are discussed for the low invasive pollen deposition on native stigmas. © The Author 2008. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.

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Production of undersized offspring in a solitary bee

Bosch J. (2008) Production of undersized offspring in a solitary bee. Animal Behaviour. 75: 809-816.
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Doi: 10.1016/j.anbehav.2007.06.018

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As predicted by Conditional Sex Allocation Theory, females of the solitary bee Osmia cornuta exposed to scarce floral resources biased their progeny sex ratio towards males, the least costly sex, and produced smaller-than-average females. Surprisingly, nesting females also produced a number of 'tiny' offspring, which contrasted with regular-sized offspring within the same nest. Developmental and wintering mortality are strongly size dependent in O. cornuta, and a high proportion of tiny offspring did not survive. This result is in disagreement with Optimal Allocation Theory, according to which resources should be allocated in portions that maximize fitness returns. I ask why did O. cornuta females build tiny provisions and why did they lay female eggs (with lower survival probability than male eggs) on these provisions. I argue that egg maturation rates and selective pressure to avoid kleptoparasitism and provision desiccation in cells left unsealed for long periods may impose a limit to the time available for cell provisioning. Under low food availability, this limit will be reached before provision sizes resulting in maximum fitness returns are attained. I also argue that the decision to fertilize an egg (and thus produce a female) is made at the beginning of the cell-provisioning process, so that females cannot adjust offspring sex to provision size. At the same time, altering the female-male cell sequence within a nest would result in fratricide because of protandric emergence. I provide evidence supporting these ecological and physiological constraints on resource allocation decisions in O. cornuta. © 2007 The Association for the Study of Animal Behaviour.

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Life Cycle Ecophysiology of Osmia Mason Bees Used as Crop Pollinators

Bosch J., Sgolastra F., Kemp W.P. (2008) Life Cycle Ecophysiology of Osmia Mason Bees Used as Crop Pollinators. Bee Pollination in Agricultural Ecosystems. : 0-0.
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Doi: 10.1093/acprof:oso/9780195316957.003.0006

Resum:

Several solitary bee species in the genus Osmia have been studied as potential pollinators of fruit trees and other early-blooming crops. Methods to manage large populations in agro-ecosystems have been developed for at least three species. This chapter reviews current knowledge on the life cycle of Osmia and emphasizes the need to establish a solid ecophysiological basis to develop adequate rearing methods for these species. Two phenological events - the timing of adult diapause in the autumn, and the timing of emergence in the spring - require particular attention when managing Osmia populations. The timing of adult diapause is critical because prewintering temperatures have a profound effect on fat body depletion, winter survival, and vigor at emergence. Timing of emergence and its synchronization with bloom of the target crop is important to maximize pollination and production of bee progeny. Both events can be adjusted with proper temperature management. © 2008 by Oxford University Press, Inc. All rights reserved.

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Spatial variation in selection on corolla shape in a generalist plant is promoted by the preference patterns of its local pollinators

Gómez J.M., Bosch J., Perfectti F., Fernández J.D., Abdelaziz M., Camacho J.P.M. (2008) Spatial variation in selection on corolla shape in a generalist plant is promoted by the preference patterns of its local pollinators. Proceedings of the Royal Society B: Biological Sciences. 275: 2241-2249.
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Doi: 10.1098/rspb.2008.0512

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An adaptive role of corolla shape has been often asserted without an empirical demonstration of how natural selection acts on this trait. In generalist plants, in which flowers are visited by diverse pollinator fauna that commonly vary spatially, detecting pollinator-mediated selection on corolla shape is even more difficult. In this study, we explore the mechanisms promoting selection on corolla shape in the generalist crucifer Erysimum mediohispanicum Polatschek (Brassicaceae). We found that the main pollinators of E. mediohispanicum (large bees, small bees and bee flies) discriminate between different corolla shapes when offered artificial flowers without reward. Importantly, different pollinators prefer different shapes: bees prefer flowers with narrow petals, whereas bee flies prefer flowers with rounded overlapping petals. We also found that flowers with narrow petals (those preferred by bees) produce both more pollen and nectar than those with rounded petals. Finally, different plant populations were visited by different faunas. As a result, we found spatial variation in the selection acting on corolla shape. Selection favoured flowers with narrow petals in the populations where large or small bees are the most abundant pollinator groups. Our study suggests that pollinators, by preferring flowers with high reward, exert strong selection on the E. mediohispanicum corolla shape. The geographical variation in the pollinator-mediated selection on E. mediohispanicum corolla shape suggests that phenotypic evolution and diversification can occur in this complex floral trait even without specialization. © 2008 The Royal Society.

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Association between floral traits and rewards in Erysimum mediohispanicum (Brassicaceae)

Gómez J.M., Bosch J., Perfectti F., Fernández J.D., Abdelaziz M., Camacho J.P.M. (2008) Association between floral traits and rewards in Erysimum mediohispanicum (Brassicaceae). Annals of Botany. 101: 1413-1420.
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Doi: 10.1093/aob/mcn053

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• Background and Aims: Floral rewards may be associated with certain morphological floral traits and thus act as underlying factors promoting selection on these traits. This study investigates whether some traits that are under pollinator-mediated selection (flower number, stalk height, corolla diameter, corolla tube length and corolla tube width) in the Mediterranean herb E. mediohispanicum (Brassicaceae) are associated with rewards (pollen and nectar). • Methods: During 2005 the phenotypic traits and the visitation rate of the main pollinator functional groups were quantified in 720 plants belonging to eight populations in south-east Spain, and during 2006 the same phenotypic traits and the reward production were quantified in 400 additional plants from the same populations. • Key Results: A significant correlation was found between nectar production rate and corolla tube length, and between pollen production and corolla diameter. Visitation rates of large bees and butterflies were significantly higher in plants exhibiting larger flowers with longer corolla tubes. • Conclusions: The association between reward production and floral traits may be a factor underlying the pattern of visitation rate displayed by some pollinators. © The Author 2008. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.

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Laboratory bioassays to evaluate fungicides for chalkbrood control in larvae of the Alfalfa leafcutting bee (Hymenoptera: Megachilidae)

Huntzinger C.I., James R.R., Bosch J., Kemp W.F. (2008) Laboratory bioassays to evaluate fungicides for chalkbrood control in larvae of the Alfalfa leafcutting bee (Hymenoptera: Megachilidae). Journal of Economic Entomology. 101: 660-667.
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Doi: 10.1603/0022-0493(2008)101[660:LBTEFF]2.0.CO;2

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Chalkbrood, a fungal disease in bees, is caused by several species of Ascosphaera. A. aggregata is a major mortality factor in populations of the alfalfa leafcutting bee, Megachile rotundata (F.) (Hymenoptera: Megachilidae) used in commercial alfalfa seed production. Four formulated fungicides, Benlate 50 WP, Captan, Orbit, and Rovral 50 WP were tested in the laboratory for efficacy against hyphal growth of A. aggregata cultures. The same fungicides, with the addition of Rovral 4 F, were tested for their effects on incidence of chalkbrood disease, and toxicity to M. rotundata larvae. Benlate, Rovral 50 WP, and Rovral 4 F reduced incidence of chalkbrood with minimal mortality on larval bees. Benlate and Rovral 50 WP also reduced hyphal growth. Orbit was effective in reducing hyphal growth, but it did not reduce incidence of chalkbrood and was toxic to bee larvae. Captan was not effective in reducing hyphal growth or chalkbrood incidence, and it was toxic to bee larvae. Fungicides that reduce incidence of chalkbrood and larval mortality in this laboratory study are candidates for further study for chalkbrood control.

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FunGicide tests on adult alfalfa leafcutting bees (Hymenoptera: Megachilidae)

Huntzinger C.I., James R.R., Bosch J., Kemp W.P. (2008) FunGicide tests on adult alfalfa leafcutting bees (Hymenoptera: Megachilidae). Journal of Economic Entomology. 101: 1088-1094.
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Doi: 10.1603/0022-0493(2008)101[1088:FTOAAL]2.0.CO;2

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Chalkbrood is a serious disease of alfalfa leafcutting bee Megachile rotundata (F.) (Hymenoptera: Megachilidae) larvae, causing upward of 20% infection in the field. The causative agent is the fungus Ascosphaera aggregata. This bee is used extensively for alfalfa seed pollination in the United States. Using laboratory bioassays, we previously demonstrated that fungicides can reduce chalkbrood levels in the larvae. Here, we evaluate the toxicity of four fungicides, Benlate, Captan, Orbit, and Rovral, to adult bees by using three different bioassays. In the first test, fungicides were applied to bees' thoraces. In the second test, mimicking foliage residue, a piece of filter paper soaked in fungicide was placed on the bottom of a container of bees. The third test evaluated oral toxicity by incorporating fungicides into a sugar-water solution that was fed to the bees. The filter paper test did not discriminate among the fungicides well, and the oral test resulted in the greatest mortality. Toxicity to males was greater than to females. The use of fungicides for chalkbrood control is a logical choice, but caution should be used in how they are applied in the presence of bees.

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Fungicide tests on adult Megachile rotundata (F.) (Hymenoptera: Megachilidae).

Huntzinger CI, James RR, Bosch J, Kemp WP (2008) Fungicide tests on adult Megachile rotundata (F.) (Hymenoptera: Megachilidae). Journal of Economic Entomology 101: 1088-1094.

Foraging and nesting behavior of Osmia lignaria (Hymenoptera: Megachilidae) in the presence of fungicides: Cage studies

Ladurner E., Bosch J., Kemp W.P., Maini S. (2008) Foraging and nesting behavior of Osmia lignaria (Hymenoptera: Megachilidae) in the presence of fungicides: Cage studies. Journal of Economic Entomology. 101: 647-653.
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Doi: 10.1603/0022-0493(2008)101[647:FANBOO]2.0.CO;2

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During orchard pollination studies in California, we observed dramatic changes in nesting and foraging behavior of Osmia lignaria Say (Hymenoptera: Megachilidae) after sprays with tank mixtures containing fungicides. A characteristic pattern of postspray events observed includes erratic behavior and interrupted foraging and nesting activity for several days. In an effort to determine whether fungicidal sprays were disruptive to bee foraging and thus to pollination, we exposed O. lignaria females nesting in field cages planted with lacy scorpionweed, Phacelia tanacetifolia Benth (Hydrophyllaceae), to selected spray mixtures normally encountered in California orchard production systems: iprodione (Rovral), propiconazole (Orbit), benomyl (Benlate), and captan (Captan 50 WP); the surfactant Dyne-Amic, alone and mixed with Rovral; and the tank mixture IDB (Rovral + Dyne-Amic + the foliar fertilizer Bayfolan Plus). An additional cage sprayed with an equal volume of water acted as control, and a cage sprayed with the insecticide dimethoate as a toxic standard. For each female O. lignaria, we recorded time spent inside the nest depositing pollen-nectar loads, foraging time, cell production rate, and survival. All females in the dimethoate treatment died postspray + 1 d. Before death, some of these females behaved similarly to our previous orchard observations. A high proportion of females in the IDB cage were inactive for a few hours before resuming normal foraging and nesting activity. No lethal or behavioral effects were found for any of the other compounds or mixtures tested. Our results indicate that the fungicide applications that we tested are compatible with the use of O. lignaria as an orchard pollinator.

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Field use of an incubation box for improved emergence timing of Osmia lignaria populations used for orchard pollination

Pitts-Singer T.L., Bosch J., Kemp W.P., Trostle G.E. (2008) Field use of an incubation box for improved emergence timing of Osmia lignaria populations used for orchard pollination. Apidologie. 39: 235-246.
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Doi: 10.1051/apido:2007061

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Wintered populations of blue orchard bees, Osmia lignaria, may require incubation to time emergence to crop bloom. In this study, bee nests were placed in an almond (California) and an apple (Utah) orchard under two incubation treatments: in wood blocks and field incubation boxes. Loose cocoons were also placed in the boxes. Incubation boxes had heating units (set to max. temperature = 22°C) to increase or prolong daytime temperatures to higher than ambient (≥ 14°C higher in Utah). Bee emergence was monitored, and temperatures were recorded. The incubation boxes allowed for faster accumulation of heat units compared to wood blocks. Bees survived well under all conditions (>90% emergence). Compared to bees in wood blocks, females in incubation boxes required three days less in CA and eight days less in Utah for 50% emergence. Results show the utility of heated incubation boxes for shortening O. lignaria emergence time, helping to synchronize bee emergence with bloom initiation. © INRA/DIB-AGIB/ EDP Sciences, 2008.

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