Mapping Alfalfa Leafcutting Bee pollen dispersal across a 2-dimensional landscape

Natalie BoyleQSME Stat Project

April 2013

Deregulation of RoundUp Ready alfalfa and implications

• RoundUp Ready has become the first open pollinated perennial crop to be deregulated by the USDA

• Its reliance on insect pollinators for seed production makes gene flow between genetically engineered (GE) and GE-sensitive crops a potential risk for growers

Deregulation of RoundUp Ready alfalfa and implications

• We want to be able to recommend pollinator management practices for domicile spacing in the field to minimize any risk of transgene movement to nontarget fields

• To do so, we must then characterize pollinator movement in a spatial setting.

• Different types of pollinators are used on alfalfa, but this model is designed to incorporate behavior of only the alfalfa leafcutting bee (ALCB), Megachile rotundata.

Alfalfa leafcutting bee (ALCB)

• Used heavily in alfalfa seed pollination due to a more efficient tripping mechanism of the alfalfa blossom over the honey bee

• Solitary bees are managed by alfalfa growers and imported from suppliers in Canada every spring

• They nest in wood or styrofoam bee boards that are housed within domiciles that sit in alfalfa fields

Alfalfa seed field

ALCB boards housed within domiciles ALCB domicile in the field

ALCB on an alfalfa blossom

Methods:

• Set out ‘trap’ styrofoam nesting blocks in multiple domiciles across the Touchet Valley of Washington (near Tri-Cities) at the start of the pollination season

• Bring styrofoam blocks back to the lab on a weekly basis and test for RR gene in the collected pollen.

We already know the composition of the agricultural landscape within the Touchet valley

EX:Let’s assume boxes are the alfalfa fields located in the Touchet Valley

RR = RoundUp ReadyConv. = conventional

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Say we were to sample pollen from a domicile located in this alfalfa field and picked up the RR gene in pollen.

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We wouldn’t be able to know from the gene which RR field the transgene came from, therefore we would not be able to determine how far ACLB flew to pick up said gene

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Ultimate goal

• The aim of my proposed model is to use what we know about ALCB foraging behavior to predict likelihood of picking up the transgene in a landscape setting.

• Find an equation to predict ALCB movement– incorporate information about the spatial

distribution of RR fields

What we know

• We already have some idea of how P(foraging) changes with distance in alfalfa seed fields:

Bee foraging generally follows a negative exponential function. This graph was created with honey bee data.

As distance from point of origin increases, P(foraging) decreases.(Figure from Hagler et al 2011)

From St. Amand et al (2000)… He used different methods to map pollen movement in alfalfa by looking for specific markers harvested alfalfa seed

I would like to be able to detect the likelihood that ALCB is foraging in one field over another.

In this example, there would be a higher probability that the transgene came from the RR field in the NW corner over the field on the east side of the conventional plot.

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12% 80%6%2%

Because this work will be performed in an upcoming field season, I will need to simulate data based on what we know about ALCB foraging behavior to develop/test the model.

• Temporal variation in foraging distance– ALCB will likely move further away from their

domicile over time as local resources become depleted

• Directional bias in foraging?– Bees may not be equally likely to forage in all

directions, given the structure of the domiciles.

Potential problems:

Developing a likelihood model in R

• Negative exponential function• Binomial distribution in which P(foraging) will

be assessed by presence/absence of RR gene• Simulate data• Develop likelihood test based on simulated

data

Thanks!