Good Fruit Grower

March 15

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Enhanced Biocontrol CODLING MOTH: It's what's for dinner. Sterilized carabid beetle before gut dissection. Investigating the predators down under using DNA gut content analysis. by Angela Gadino, Tom Unruh and Jay Brunner D o you ever wonder what those earwigs, spiders, and other ground-dwelling predators eat in your orchard? This question has been a main focus in the Enhancing Biological Control in Western Orchards Specialty Crop Research Initiative project. We know these predators are in our orchards, but up until now who is eating what has not been well documented, especially with regards to codling moth. We set out to look at which major predator groups found commonly in western orchards might be eating the most codling moth larvae. Codling moth larvae, once fully grown inside apples or pears, leave the fruit during summer and fall and seek cocooning sites from which they either emerge as second-generation adults or overwinter as mature larvae until the following spring. The cocooned larvae can be found in bark crevices on trees, on props, or in leaf litter and other organic matter on the orchard floor. Generalist predators active in the tree canopy, the trunk, or on the ground may discover and feed on codling moth larvae in these places. We believe that predation on these codling moth larvae, either moving to or in cocooning sites, can help reduce population levels in the following season. However, we needed real numbers to support our beliefs. But what is the best way to determine which of the predators we find in orchards are eating codling moth larvae in the field? Many of these lower canopy and ground-dwelling predators are cryptic in their feeding behaviors. Most predators are only actively hunting for prey during the night, and they like to hide in cracks, crevices, ground cover, leaf litter, or soil. Also, unlike parasitism, it is difficult to find evidence of predation since usually the whole body of the prey is consumed. Fortunately, new molecular technologies allow us to analyze the gut content of predators, which gives us a better picture of who is eating codling moth. The technique is relatively straightforward, using a primer in a PCR (polymerase chain reaction) analysis that amplifies any codling moth DNA that occurs in the gut content of each predator tested. The tricky part is capturing the predators in the orchard and collecting them before they have the chance to fully digest their prey so there is still DNA material available to analyze. Dissecting a carabid beetle to remove gut contents. Gut content samples after homogenizing with buffer solution. Placing gut content of a dissected carabid beetle into a vial for DNA analysis. 14 March 15, 2013 GOOD FRUIT GROWER PHOTOS by ANGELA GADINO, WSU Pitfall traps To do this, we used pitfall traps, which are plastic cups sunk into the soil, where the lip of the cup is level with the ground so unsuspecting insects will fall into the traps. Since most of these predators are active at night, the insects or spiders captured in the cups were collected each morning. The samples were then brought to the laboratory where they were sorted into groups and frozen until ready for analysis. The molecular analysis consists of two main parts. First, the frozen specimens were thawed, sterilized, and placed into small plastic vials and homogenized with a buffer solution. For some of the larger species, like ground beetles, the guts were dissected and used instead of the whole insect body. The homogenized samples were then ready to undergo PCR amplification, allowing us to detect codling moth DNA. Polymerase chain reaction analysis consists of several steps Preparing gut content samples for spiders, earwigs, and carabid beetles for DNA analysis.

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