MSU Extension Fruit & Nuts

In this video we will demonstrate how to use the filter method for sampling for spotted wing-drosophila larvae in blueberries. This is a quick and easy sampling method that growers, scouts, and extension agents can use to determine whether larvae are present in their fruit. While this video shows how to use this method for blueberries, it can be used for other fruits such as raspberries, blackberries or cherries. Dr. Rufus Isaacs from Michigan State University will be talking through the different steps of this method in this video. We begin with the first step, picking ripe fruit in the field. So today I'm going to demonstrate the salt filter method with these blueberries here that we have at the Trevor Nichols Research Center in Fennville, MI. These are ripe now, so it's time to start sampling them to see if they have spotted wing drosophila larvae in them and we're going to demonstrate this method to you today. So typically what we would do is sample from an area like this. This is up next to a woods, so it's likely to have a bit more pressure than other parts of the field. So we sample and take a minimum minimum of 4 to 8 ounces of fruit. So these are ripe blueberries and already taking some of them, but you can see we would just go through the bushes a nd take the sample of ripe berries from around this area. And then we might take multiple samples from the field as well if we wanted to see different cultivars had different levels, or if different parts of the farm had different levels of SWD infestation. So put it in this container, mark it. I've got the field number here and the date, and that can just keep track of the sample later on as we go through this processs. For the second step, Rufus will demonstrate how to process the blueberries once all of the samples have been picked. OK, so we just picked these fruit from the field, these blueberries, fresh blueberries that we're checking to see if they have spotted-wing drosophila larvae in them and we do that by giving them just a light pressing to get them ready for this test. We don't want to squish them because then that will plug up the filters later. But we're going to take these two samples do that light pressing action and then this is a solution of salt water. We have one cup per gallon of salt water here so it's a strong solution and we pour that in to cover the berries. You can see there we've got two containers the liquid is covering those berries and then we can leave this solution together for like 30 minutes i s the minimum. We often do an hour because that increases the chance that we'll get all the larvae out of there so these can incubate with the salt solution and the blueberries for an hour. And then the salt solution is useful because that actually kills the larvae and then they're able to be seen. If you use just tap water, they'll be wriggling around inside your filter when you're looking at them later. So that's the difference with the solutions you could use just water, but we we like the salt water that kills those larvae in the in the filter. So next step will be to run this through the filter and then we'll look at it under the microscope. In this third step, Rufus will show how to sift the blueberries and salt water through a funnel so that the larvae get caught in the coffee filter. All right, so this is now, this sample has now sat in the liquid for an hour, and we're going to run the fruit and the liquid through there. So that separates the liquid from the fruit. And then we'll take this and give them a wash and an agitation to make sure all the larvae that might be in there come off. And then we can now separate the fruit and that sample can be thrown away. And the larvae, if there are any, should be in this filter that we're going to look at under the microscope. Before we proceed to looking for larvae using a microscope, we are going to take a look at how the sampling process looks in real time. In this case, we have a number of samples ready to be sifted on the left hand side, A bucket for the waste fruit is on the right hand side, and a garden hose with a spray nozzle attachment is easily within reach. With everything close at hand, it takes very little time to process each of these samples. Before we move on, we are going to quickly run through the supplies that are being used in this fruit processing step. The funnel that is being used is a 2 1/2 inch by 10 inch funnel. Inside the bottom of the funnel is a piece of wire mesh. The purpose of the mesh is to keep the fruit in the funnel while the salt water and larvae fall down into the coffee filter. For this video we are using wire mesh that has a hole size of approximately 0.08 inches. The coffee filter we are using is a four-cup reusable coffee filter with a wire mesh bottom. All of these supplies are readily available from online suppliers, or you can adapt this method as needed for your particular situation. Now we are going to move on to using a microscope to look for larvae in the coffee filters. For this step, we are going to use a stereo microscope to look for larvae in the coffee filters. The microscope shown here has a 10X eyepiece and a 0.5 X objective lens. This provides just enough magnification to easily see the very small larvae, but still allows us to have the entire coffee filter in the field of view. This makes looking for and counting larvae a quick and easy process. Microscopes similar to this one can be easily purchased online. While some microscopes can cost thousands of dollars, there are much cheaper options available that will only cost a few $100, and they will work just as well for looking for larvae. However, if you do not have a microscope or do not want to use one, you can also just visually inspect the bottom of the coffee filter for larvae. While you will not be able to see the very smallest larvae, you will still be able to see the medium and large larvae. If you do decide to proceed with only visually inspecting your coffee filters, make sure you have good lighting as that will help you to see more of the larvae in the filter. Once you have looked at all of your coffee filters, you can write down all of the larvae that you found, or write down zeros if you did not find any larvae. You can use this information in a number of ways, including making decisions on when to spray insecticides and what products to use. You can also use the information to make decisions on other aspects of your operation, such as whether to change when you harvest your fruit. Overall, this method is a quick and easy way to sample for spotted-wing drosophila larvae in your fruit. It's another tool in your toolbox that can be used to help you make management decisions on your farm. If you would like more information on the filter method for sampling for spotted-wing d rosophila, here are some resources you can explore. On the left are two peer reviewed articles that have been published on this topic and on the right are some links to supplies that are used in this method. Please note that these supplies links are provided to show examples of products you can use and do not constitute the endorsement of any products or supplier companies. Finally, we would like to thank the organizations who helped fund the development of this technique and the making of this video, including the USDA Specialty Crops Research Initiative, Project Green, and the Michigan Blueberry Commission. We also would like to thank the Trevor Nichols Research Center for hosting this video. If you would like more information on spotted-wing drosophila, please visit the swdmanagement.org website. Thank you for watching this video.