Dataset Information

Movement of soil-applied imidacloprid and thiamethoxam into nectar and pollen of squash (Cucurbita pepo).

ABSTRACT: There has been recent interest in the threat to bees posed by the use of systemic insecticides. One concern is that systemic insecticides may translocate from the soil into pollen and nectar of plants, where they would be ingested by pollinators. This paper reports on the movement of two such systemic neonicotinoid insecticides, imidacloprid and thiamethoxam, into the pollen and nectar of flowers of squash (Cucurbita pepo cultivars "Multipik," "Sunray" and "Bush Delicata") when applied to soil by two methods: (1) sprayed into soil before seeding, or (2) applied through drip irrigation in a single treatment after transplant. All insecticide treatments were within labeled rates for these compounds. Pollen and nectar samples were analyzed using a standard extraction method widely used for pesticides (QuEChERS) and liquid chromatography mass spectrometric analysis. The concentrations found in nectar, 10 ± 3 ppb (mean ± s.d) for imidacloprid and 11 ± 6 ppb for thiamethoxam, are higher than concentrations of neonicotinoid insecticides in nectar of canola and sunflower grown from treated seed, and similar to those found in a recent study of neonicotinoids applied to pumpkins at transplant and through drip irrigation. The concentrations in pollen, 14 ± 8 ppb for imidacloprid and 12 ± 9 ppb for thiamethoxam, are higher than those found for seed treatments in most studies, but at the low end of the range found in the pumpkin study. Our concentrations fall into the range being investigated for sublethal effects on honey bees and bumble bees.

SUBMITTER: Stoner KA

PROVIDER: S-EPMC3384620 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Movement of soil-applied imidacloprid and thiamethoxam into nectar and pollen of squash (Cucurbita pepo).

Stoner Kimberly A KA Eitzer Brian D BD

PloS one 20120627 6

There has been recent interest in the threat to bees posed by the use of systemic insecticides. One concern is that systemic insecticides may translocate from the soil into pollen and nectar of plants, where they would be ingested by pollinators. This paper reports on the movement of two such systemic neonicotinoid insecticides, imidacloprid and thiamethoxam, into the pollen and nectar of flowers of squash (Cucurbita pepo cultivars "Multipik," "Sunray" and "Bush Delicata") when applied to soil b ...[more]

PMID: 22761727

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Project description:Background and aimsNectar is a very complex mixture of substances. Some components (sugars and amino acids) are considered primary alimentary rewards for animals and have been investigated and characterized in numerous species for many years. In contrast, nectar proteins have been the subject of few studies and little is known of their function. Only very recently have detailed studies and characterization of nectar proteins been undertaken, and then for only a very few species. This current work represents a first step in the identification of a protein profile for the floral nectar of Cucurbita pepo. In this regard, the species studied is of particular interest in that it is monoecious with unisexual flowers and, consequently, it is possible that nectar proteins derived from male and female flowers may differ.MethodsManually excised spots from two-dimensional (2-D) electrophoresis were subjected to in-gel protein digestion. The resulting peptides were sequenced using nanoscale LC-ESI/MS-MS (liquid chromatography-electrospray ionization/tandem mass spectrometry). An MS/MS ions search was carried out in Swiss-Prot and NCBInr databases using MASCOT software.Key resultsTwo-dimensional electrophoresis revealed a total of 24 spots and a different protein profile for male and female flower nectar. Four main proteins recognized by 2-D electrophoresis most closely resemble β-d-xylosidases from Arabidopsis thaliana and have some homology to a β-d-xylosidase from Medicago varia. They were present in similar quantities in male and female flowers and had the same molecular weight, but with slightly different isoelectric points.ConclusionsA putative function for xylosidases in floral nectar of C. pepo is proposed, namely that they may be involved in degrading the oligosaccharides released by the nectary cell walls in response to hydrolytic enzymes produced by invading micro-organisms. Several types of oligosaccharides have been reported to increase the pathogenic potential of micro-organisms. Thus, it is possible that such a mechanism may reduce the virulence of pathogens present in nectar.

Project description:We have identified a kind of parthenocarpy in zucchini squash which is associated with an incomplete andromonoecy, i.e. a partial conversion of female into bisexual flowers. Given that andromonoecy in this and other cucurbit species is caused by a reduction of ethylene production in the female flower, the associated parthenocarpic development of the fruit suggested the involvement of ethylene in fruit set and early fruit development.We have compared the production of ethylene as well as the expression of 13 ethylene biosynthesis and signalling genes in pollinated and unpollinated ovaries/fruits of two cultivars, one of which is parthenocarpic (Cavili), while the other is non-parthenocarpic (Tosca). In the latter, unpollinated ovaries show an induction of ethylene biosynthesis and ethylene signal transduction pathway genes three days after anthesis, which is concomitant with the initiation of fruit abortion and senescence. Fruit set and early fruit development in pollinated flowers of both cultivars and unpollinated flowers of Cavili is coupled with low ethylene biosynthesis and signalling, which would also explain the partial andromonoecy in the parthenocarpic genotype. The reduction of ethylene production in the ovary cosegregates with parthenocarpy and partial andromonoecy in the selfing progeny of Cavili. Moreover, the induction of ethylene in anthesis (by ethephon treatments) reduced the percentage of bisexual parthenocarpic flowers in Cavili, while the inhibition of ethylene biosynthesis or response (by AVG and STS treatments) induces not only andromonoecy but also the parthenocarpic development of the fruit in both cultivars.Results demonstrate that a reduction of ethylene production or signalling in the zucchini flower is able to induce fruit set and early fruit development, and therefore that ethylene is actively involved in fruit set and early fruit development. Auxin and TIBA treatments, inducing fruit set and early fruit development in this species, also inhibit ethylene production and the expression of ethylene biosynthesis and response genes. A model is presented that discusses the crosstalk between ethylene and auxin in the control of fruit set and early fruit development in zucchini squash.

Dataset Information

Movement of soil-applied imidacloprid and thiamethoxam into nectar and pollen of squash (Cucurbita pepo).

Publications

Movement of soil-applied imidacloprid and thiamethoxam into nectar and pollen of squash (Cucurbita pepo).

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