## Abstract

### Economic Cost–Benefit Model Synthesis for Pest Control and Pollination

Using the insecticide treatment reduction and pollination increase data, we created a cost–benefit model for a hedgerow installation bordering two typical, 16-ha crop fields (one on each side). We have observed that it takes ∼3 yr before plants are mature with floral resources, and therefore, net benefits were calculated starting at Y > 3. Estimated economic benefit to growers for establishing hedgerows, for each year ( Y ) after the third year of establishment was calculated as:

(3)
$BY={∑Y=4Y[(PP+PPC1.05Y]}−C$
Where B Y is the estimated net economic benefit in dollars per field at Y years, starting at Y  = 4, from the time of initial restoration, P p is the mean profit increase resulting from differential pollination deficit, between control and hedgerow sites, P PC is the average profit change attributed to having a restored hedgerow adjacent to the field for pest control, and C is the cost of establishing and maintaining a 305-m hedgerow for the first three years. We took into account the time value of money (i.e., that money available now is worth more than the same amount in the future), and the uncertainty of future returns by applying a discount rate of 5%, such that profit each year was divided by 1.05 Y .

## Results

### Valuation of Pest Control Services

In 2009, one tomato field in the control group was treated for aphids. In 2010, three control fields and one hedgerow field reached the threshold for aphid treatment in our assessments. In total therefore, four of the eight control tomato fields and one of the eight hedgerow tomato fields reached thresholds and were treated for aphids. Using an average cost of one treatment for aphids of US$43.24/ha ( Miyao et al. 2008 ), it would cost ∼US$692 to treat a 16-ha field for aphids. With 4/8 or half of control fields needing treatment, that equals an average cost of US$346 per control field. When only 1/8 hedgerow fields require treatment for aphids, average costs for aphid control on hedgerow fields is US$86, 75% less per field than control fields. Although we sampled 200 m into fields from hedgerows, we calculated potential savings to a 16-ha field (400 by 400 m 2 ), as there was no decline in pest suppression of aphids up to the distance we measured (200 m from hedgerows; Morandin et al. 2014 ).

Few pests, other than aphids, were observed in our tomato fields at economic treatment threshold levels in the years of this study. Some fields were treated with sulfur for tomato russet mites ( Aculops lycopersici (Massee)); however, we did not include this in our model because these mites are not effectively controlled by natural enemies and therefore their populations would not be impacted by the presence of hedgerows (University of California Integrated Pest Management [ UC IPM] 2013 ).

### Valuation of Pollination Services

The number of replicated pollinator visits for the canola pollination efficiency study was between 31 and 83 for all groups except the CSM group, “small dark bees” which only had 12 replicate visits. Pollination efficiency of each group, based on seed set from one visit from an individual of that group (number in brackets is average seeds per pod from one visit), was honey bees (3.0), syrphid flies (3.1), striped sweat bees (3.0), tiny dark bees (2.6), small dark bees (2.8), and hairy legged bees (2.9), with no significant differences between any group ( F5,288  = 0.11, P  = 0.99; Table 1 ).

Table 1.

Mean seeds per pod (±SE) from one floral visit by each pollinator group on canola, B. rapa

Pollinator group a Average seeds per pod from one floral visit (±SE) No. of replicates
Honey bees 3.0 ± 0.39 60
Syrphid flies 3.1 ± 0.43 54
Striped sweat bees 3.0 ± 0.41 54
Tiny dark bees 2.6 ± 0.28 83
Small dark bees 2.8 ± 0.82 12
Hairy legged bees 2.9 ± 0.52 31
Pollinator group a Average seeds per pod from one floral visit (±SE) No. of replicates
Honey bees 3.0 ± 0.39 60
Syrphid flies 3.1 ± 0.43 54
Striped sweat bees 3.0 ± 0.41 54
Tiny dark bees 2.6 ± 0.28 83
Small dark bees 2.8 ± 0.82 12
Hairy legged bees 2.9 ± 0.52 31

Pollinator efficiency was not significantly different among groups, P = 0.99.

a The different types of flower visitors were recorded in CSM categories described in Kremen et al. (2011) .

In the studies with sentinel canola plants in the crop fields, there was no difference in total abundance of visitors on B. rapa flowers between hedgerow and control sites ( Fig. 1 ). However, there was a greater abundance of native bees observed on B. rapa plants at hedgerow than control sites ( F1,14  = 26.06, P  = 0.0002). Because overall floral visitor abundance was not different between field types, we did not see differences in seed set between fields with and without hedgerows. We used the relationship between floral visitors and seed set to estimate seed set differences due to differences in native bee abundance differences. The best-fit relationship between observed floral visitors and seed deficit was an exponential decay equation: y = 0.45exp(−0.128x) ( R2adj  = 0.42, F1,118  = 77.1, P  < 0.0001; Fig. 2 ).

Fig. 1.

Mean floral visitors (+SE) observed during 4-min visual observations on B. rapa sentinel canola plants in processing tomato fields adjacent to hedgerows or control (conventionally managed) field edges. Stars above a pair of bars indicate a difference in abundance for that group between treatments ( P  < 0.05).

Fig. 1.

Mean floral visitors (+SE) observed during 4-min visual observations on B. rapa sentinel canola plants in processing tomato fields adjacent to hedgerows or control (conventionally managed) field edges. Stars above a pair of bars indicate a difference in abundance for that group between treatments ( P  < 0.05).

Fig. 2.

Relationship between pollination deficit (maximal seed set minus open seed set, divided by maximal seed set at each grouping of four canola plants) and the observed abundance of floral visitors (honey bees, native bees, and syrphid flies) on B. rapa at four fields with hedgerows and four fields with conventionally managed edges (control) in each of two years, 2010 (open circles) and 2011 (closed circles).

Fig. 2.

Relationship between pollination deficit (maximal seed set minus open seed set, divided by maximal seed set at each grouping of four canola plants) and the observed abundance of floral visitors (honey bees, native bees, and syrphid flies) on B. rapa at four fields with hedgerows and four fields with conventionally managed edges (control) in each of two years, 2010 (open circles) and 2011 (closed circles).

Crop yields vary widely based on agronomic conditions; however, we used an average yield of 1,200 kg/ha and the 2011–2012 average value of canola seed at US$600/ton (US$0.60/kg) to calculate an average value from canola production of US$720 per hectare ( http://www.canolacouncil.org/markets-stats/statistics/ ). Input costs for non-GM canola were ∼US$300/ha resulting in a net profit of ∼US$420/ha. When we removed the estimated seed set resulting from honey bee and syrphid fly visits, field treatment (hedgerow or control edge) affected proportional seed deficit ( $χ2(1)$ = 10.5, P = 0.001). Using the mean values for seed deficit considering only native bees ( PI = 0.21), there was a 21 ± 4.9% (standard error) seed increase at hedgerow sites due to enhanced native bee populations. Therefore, if a hedgerow were present, greater pollination from enhanced native pollinator populations would increase yields 21% to 1,452 kg/ha and a net profit of US$571/ha, which represents a US$151 profit increase, per hectare, over no hedgerows. As in Morandin and Winston (2006) , we acknowledge that harvest and transport costs could increase slightly with greater yield; however, this likely would be a small amount and we do not factor it in. Using the above values, profit from a 16-ha canola field with a conventional edge would be US$6,720. With the pollination increase from native bee enhancement by hedgerows (in an area with no managed honey bees or other effective pollinators), profit would be increased on a field by US$151/ha (from US$420/ha to US$571/ha, or 36% increase) resulting in a profit increase of US$2,416 per 16-ha field.

Overall profit therefore, from the combined benefits of increased pollination and fewer pest control treatments over time will help offset the costs of a 305-m hedgerow plantings as shown in Fig. 3 . Scenario 1 shows the benefits from reduction in insecticide treatments alone each year (either no pollinator-dependent crops in the rotation or managed honey bees in the system provide all pollination needs). Scenario 2 is identical to scenario 1 but includes a 50% USDA EQIP cost share program. Scenario 3 depicts benefits from reduction in insecticide treatments each year and enhanced pollination in a pollinator-dependent crop every 3 yr. Like Scenario 2, Scenario 4 is identical to Scenario 3, but includes a 50% USDA EQIP cost share program.

Fig. 3.

Discounted profit (US$1.05% discounted rate per annum) from installation of a 305-m hedgerow of native California flowering plants on a field crop edge, calculated from the cost of installation and potential cost savings incurred from hedgerows from reduction in insecticide application and pollination benefits from natural enemies and pollinators. Scenario 1: benefits from reduction in insecticide treatments alone each year (either no pollinator-dependent crops in the rotation or managed honey bees in the system provide all pollination needs). Scenario 2: same as Scenario 1 but with a 50% USDA EQIP cost share program. Scenario 3: benefits from reduction in insecticide treatments each year and enhanced pollination in a pollinator-dependent crop every 3 yr. Scenario 4: same as Scenario 3 but with a 50% USDA EQIP cost share program. We do not show a potential for cost benefit from reducing the number of honey bee hives needed for pollination. However, a grower could also gain from the enhancement of native bees if they needed to rent fewer honey bee hives. Hedgerows were planted on field borders, so there was no loss in crop production. (Online figure in color.) Fig. 3. Discounted profit (US$ 1.05% discounted rate per annum) from installation of a 305-m hedgerow of native California flowering plants on a field crop edge, calculated from the cost of installation and potential cost savings incurred from hedgerows from reduction in insecticide application and pollination benefits from natural enemies and pollinators. Scenario 1: benefits from reduction in insecticide treatments alone each year (either no pollinator-dependent crops in the rotation or managed honey bees in the system provide all pollination needs). Scenario 2: same as Scenario 1 but with a 50% USDA EQIP cost share program. Scenario 3: benefits from reduction in insecticide treatments each year and enhanced pollination in a pollinator-dependent crop every 3 yr. Scenario 4: same as Scenario 3 but with a 50% USDA EQIP cost share program. We do not show a potential for cost benefit from reducing the number of honey bee hives needed for pollination. However, a grower could also gain from the enhancement of native bees if they needed to rent fewer honey bee hives. Hedgerows were planted on field borders, so there was no loss in crop production. (Online figure in color.)

## Discussion

All of our hedgerows or control edges had crops on either side of them, usually with both fields owned by the same grower, and therefore we modeled benefits to two, 16-ha fields on either side of the hedgerow. Due to crop rotations, we modeled a situation in which the adjacent crops would benefit from natural pest control services and a reduction in insecticide use every year (at the rate calculated for a processing tomato field although the benefit could be greater or less depending on the actual crop present). The enhanced profit from native bee enhancement would only be realized if pollination was deficient prior to native hedgerow installation, unlikely if managed honey bees or other pollinators such as syrphid flies were abundant in the area and efficient pollinators of the crop (such as in our case where there were abundant managed honey bees and syrphid flies, both efficient pollinators of B. rapa ). Therefore, Scenarios 1–2 ( Fig. 3 ) account for hedgerow installation cost return from reduced pest control costs only, and assume either crops that do not benefit from pollination or a situation where pollination is saturated already from wild and or managed pollinators.

However, as has often been shown to be the case in simplified agricultural landscapes, pollination is a limiting factor to seed set ( Kremen et al. 2002 , Long and Morandin 2011 , Klein et al. 2012 ), and seed set is increased in the presence of enhanced native bee populations ( Klein et al. 2003 , Kremen et al. 2004 , Morandin and Winston 2006 ). In addition, with current uncertainty in managed honey bee supply, it is important to understand input of native bees and ways to enhance their populations and pollination contribution to add resilience in cropping systems ( Garibaldi et al. 2011 , Winfree 2013 , M’Gonigle et al. 2015 ). This information is vital because recent overwintering losses of managed honey bee colonies in many parts of the world ( vanEngelsdorp et al. 2009 , Neumann and Carreck 2010 ) and a 300% increase in the proportion of crops requiring pollination ( Aizen and Harder 2009 ) has resulted in uncertainty as to whether managed honey bees can meet future global crop pollination requirements. Furthermore, a recent data synthesis found that crop yields around the world are responsive to increases in native pollinator visitation rates but not to increases in honey bee visitation rates ( Garibaldi et al. 2013 ). Syrphid flies were also efficient pollinators of the canola plants in our study, but we did not include them in our cost–benefit model because their numbers are highly variable from year to year in California, so cannot be relied on for crop pollination (N. M. Williams, personal communication). In addition, abundances in fields are not affected by the presence of hedgerows ( Morandin and Kremen 2013 ). Their somewhat greater abundance in control fields than in fields adjacent to hedgerows in our study was likely due to greater aphid abundance in control fields ( Morandin et al. 2014 ).

In Scenarios 3–4, we show economic benefit of hedgerows if crop rotations include pollinator-dependent crops and managed honey bees in the system do not provide all pollination needs. We factored in the pollination benefit only once every third year, to account for crop rotation of nonpollinator-dependent crops two out of three years, by reducing the pollination enhancement benefit by 1/3rd each year on both sides of the hedgerow. Although not significant, visual inspection of a boxplot of the interaction between distance and treatment on seed deficit showed a slight increase in seed deficit at hedgerow sites at the 100 and 200 m distances (still significantly lower than at control sites that had constant seed deficit at all distances). To keep our cost return estimates conservative, we therefore only applied the pollination benefit to the first 200 m of the field (8 ha).

We did not include potential reduction in cost of honey bee hive rental in our profit equations for the scenarios where managed honey bees are abundant in the landscape because of the inability from our data to make accurate predictions in the amount of reduction in hive rental that would be possible from enhancement of native bees with hedgerow restoration. However, hive rental reduction could greatly increase profit from hedgerows.

Cost return, using a 5% discount rate per year, to the grower in this case would take about 16 yr if the grower paid for the full amount of the hedgerow with only the savings that we observed from reduced insecticide application ( Fig. 3 ). However, with a 50% cost share such as EQIP, a grower would break even in costs and return at ∼9 yr postinstallation, less than the age of the hedgerows in this study. Thus, in situations where pollinator-dependent crops are not within the rotation, based on insecticide application savings calculated for processing tomato, growers likely will recuperate their initial investment in hedgerow restoration, especially when a cost-share program is used. When we modeled a situation in which we exclude pollinators other than native bees, simulating an environment with no managed pollinators or efficient pollinators other than native bees, cost return times decrease substantially to 5 yr and 7 yr (with and without cost-share programs, respectively).

This cost–benefit model is a starting point for valuing the economic benefit of multiple ecosystem services resulting from on-farm restoration in highly simplified agricultural landscapes. The value could be an over or under estimate for multiple reasons. These values could be underestimates of benefits of hedgerows to growers because costs can be comprehensively estimated, while total benefits are multifaceted and comprehensive estimation is beyond the scope of any one study ( Olson and Wackers 2007 ). Specifically, we have not valued the impact of natural enemies on multiple pests in tomatoes. For example, we conducted a sentinel stink bug egg parasitism experiment in order to assess differences in parasitism between control and hedgerow sites ( Morandin et al. 2014 ). We found greater parasitism up to 100 m into hedgerow sites than control sites. However, from this experiment, it was not possible to extrapolate to direct economic impact and cost savings from reduced pesticide use because stink bug levels remained below economic treatment thresholds during the years of this study. Also, there is the potential that enhancement of native bee populations may reduce the need for honey bee hive rental, a possible important savings with high rental costs and supply uncertain due to honey bee health issues. Further, some crops, in some areas, may benefit more from pollination enhancement by native bees and pest control than the crops and location that we used to create this model. And finally, other ecosystem services potentially provided by hedgerows, such as water quality enhancement through filtration of sediments and other pollutants, are not part of this study.

Our economic analysis could also be an overestimate in agroecosystems with crops where pest control protocols are preemptive rather than dictated by pest levels in individual fields, such as when insecticides are applied prophylactically as in neonicotinoid seed treatments ( Douglas and Tooker 2015 ). This problem could be mitigated if more growers and pest advisers used IPM protocols and pest threshold levels when making pesticide use decisions on crops. Overestimates may also occur in agroecosystems with few crops that require or benefit from pollination services or have their pollination needs met with managed honey bees.

We may also be overestimating the pollination impacts by using sentinel canola plants and scaling up to whole field crop systems. In using sentinel canola plants within a pollinator independent tomato crop, the canola may have concentrated available pollinators, which could lead to overestimation of the pollination service when scaled up to the field scale. The same number of pollinators, spread over a much larger field of canola, might have a much smaller effect on pollination. In addition, manual pollination can result in a greater number of seed and seed size, requiring a greater allocation of plant resources, resulting in an overestimate of pollination limitation ( Zimmerman and Pyke 1988 , Knight et al. 2006 ). However, Morandin and Winston (2005) found there was no decline in seeds per fruit in open-pollinated canola ( B. rapa and B.napus ) compared with manually cross-pollinated flowers, so we do not believe this was the case for our study.

Our research demonstrated that small-scale restorations can be cost effective, and provide profit to land owners in simplified agricultural landscapes. Using this, or similar models, data on pollination and pest control service enhancement from hedgerow or other habitat augmentation on multiple crops can be used to calculate cost return times and profit in a variety of situations for growers. In addition, other ecosystem service benefits could be added to these cost–return calculations. While the data derived from our study area in Yolo County, CA, show revenue after 5 to 16 yr, the cost–benefit model can vary depending on local conditions, including farm management and crop rotations ( Sardiñas and Kremen 2015 ). As a result, more long-term monitoring of crop yield, pollination levels, and pest populations on farms with and without hedgerows are needed. This model is a starting point for evaluating multiple ecosystem service benefits and economic return of within farm habitat enhancement to help minimize risks of investments. It can be applied to any agroecosystem where pest, natural enemy, and pollinator abundances are impacted by farmland habitat restoration.

## Acknowledgments

We thank our grower cooperators for allowing us to work on their farms. We thank S. Kaiser, H. Wallis, S. Ambercrombie, L. Swain, and R. Hanifin for assistance with data collection, specimen processing, and data entry, and K. Steinmann for advice on the manuscript. The research was funded by an NSERC Postdoctoral Fellowship to L.A.M., a Conservation Innovation Grant to C.K. and the Xerces Society, National Science Foundation grant (DEB 0919128) and a National Geographic Society Research and Exploration grant to L.A.M. and C.K.

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