Understanding the influence of alternate hosts and harvested blocks on SWD populations and SWD fruit preference

Project goal:  To determine if adjacent sweet cherry blocks or alternate hosts influence SWD populations in tart cherry and determine if SWD have a preference for certain hosts.

Project description:  Data suggest that SWD have host preferences that may increase their reproductive success.  This project investigated wild host or other non-commercial fruit adjacent to orchards and the impact on SWD population growth in neighboring tart cherry blocks.  In 2016, we conducted transect studies at 10 tart cherry orchards in northwest Michigan to evaluate adult SWD movement and infestation of fruit.  Five of the selected tart cherry orchards were located less than 50m from a commercial sweet cherry orchard, and there were no woodlots or other type of wooded landscape between these blocks.  Two transects of standard SWD traps baited with effective commercial lures were placed in a line perpendicular to the interface between sweet and tart cherries. We used ten traps per transect.  Traps were placed at five row intervals approximately 100m into both the tart and sweet cherry orchards.  Traps were monitored weekly from 1 June through 15 August. We sampled for larvae in fruit weekly from straw color in sweet cherries through tart cherry harvest. 

Similar methods were used to evaluate SWD populations in non-crop hosts.  We identified at least three non-crop host plants that are adjacent to a commercial tart cherry orchard and placed a trap at these sites.  This was replicated at five sites in northwest Michigan.  Traps were placed in selected non-crop host plants. The hosts were selected to create a transect from the wooded area into the orchard center.  Five traps were placed into the orchard from the edge into the middle of the block.  Traps were monitored weekly from 1 June through 15 August.  We sampled for larvae in fruit of the non-crop hosts as the fruit began to ripen (~30 June) through tart cherry harvest.

In 2016 and 2017, we conducted choice and no-choice lab bioassays to determine if SWD have a preference for certain fruit.  No-choice bioassays were conducted on Montmorency and Balaton tart cherry; Emperor Francis, Gold, Regina, and Ulster sweet cherry; and the wild hosts: mulberry, black raspberry, honeysuckle, and raspberry.  Each type of fruit was collected throughout it’s ripening process, from green to ripe.  At each collection, fruit was tested for firmness, average weight, and brix.  Seven fruit were added to the deli cup bioassay chamber and exposed to male and female SWD adults for 48 hours.  The fruit was tested for larvae with the brown sugar extraction method after 5+ days.  Choice tests were conducted in bug tents where multiple ripenesses or varieties of fruit were added.  The fruit was exposed to 10 male and 10 female SWD adults for 48 hours and the fruit was sampled for larvae after 5+ days.    We also looked at SWD preference in a choice test comparing already infested fruit to non-infested fruit.

Results: SWD Research Update 2018

Project lead/collaborators: Nikki Rothwell, Emily Pochubay, and Larry Gut

Funding sources:  Project GREEEN and Michigan Cherry Committee

Start year: 2016

End year: 2017