Issue link: https://read.dmtmag.com/i/603228
70 DECEMBER 2015 Good Fruit Grower www.goodfruit.com pathologist Kerik Cox is working to identify pathogenic fungi and bacteria associated with the beetle, which may be the real killer of infected trees. USDA researchers Louella Castrillo and John Vandenberg are also involved, looking for biological control agents and better traps. Insecticides labeled against tree borer species may be used, but applications must be closely timed with beetle attacks or made repeatedly or have long residual activity, Breth said. Previous research done by USDA researcher Christopher Ranger shows that systemic insecticides do not work. Interesting biology The black stem borer larvae don't feed on the tree but on a symbiotic fungus, Ambrosiella hartigii, which the mother beetle, called the foundress, carries with her to line the chamber in the sapwood or heartwood inside the 1-millimeter (1/25-inch) diameter hole she bores into the tree. She hollows out a channel in which to lay eggs. After she has filled the chamber with eggs (about 18) and the fungal food source is adequate for the brood, she backs out and dies, leaving her body to plug the hole. "Therefore, we can't evaluate treatments by counting dead borers," Breth said. Inside the chamber, eggs hatch into larvae that develop into about ten females for every male. It takes about 30 days for the insect to develop from egg to adult in optimal conditions but typically longer under natural conditions. The flightless males mate with the females, which leave the chamber to become new foundresses. There are two generations per year, with the last gen- eration overwintering as adults in galleries at the base of infested trees. "In late summer, the beetles migrate to a hole lower on the trunk to overwinter—as many as 100 in one chamber. The beetles go into diapause and are not active again until the next spring," Breth said. Females emerge to infest new sites starting in late April, after two or three days with temperatures above 68 °F. In 2014, activity began about May 13, and peak emergence occurred June 11, Agnello said. The first generation of adults emerged July 9-23 and the second August 20, but activity continued through September 16. This year, first flight activity was noted about May 5, with a peak at the beginning of June. Monitoring Growers should look for toothpick-like strands of frass—made of compacted sawdust from the channels— that can be seen sticking out from infected trunks after calm, rainfree days. Bark around new holes is often dis- colored and blistered, but not always, and oozing sap can be seen around the holes. Julianna Wilson, Michigan State University's IPM coordinator, advises scouting with traps made from inverted clear plastic bottles baited using one of these three methods: —Squirt about a quarter cup of ethanol-based hand sanitizer (unscented) into the cap end (bottom) of your trap. —With the bottle capped, pour in a cup of cheap vodka through one of the holes made in the side of the trap. —Purchase a ready-made ethanol lure to hang inside the trap and fill the bottom of the trap with soapy water. Hang traps on the edge of woods next to an orchard and inside orchards, and check them weekly. Beetles are very tiny and require the use of a microscope and training to identify them correctly, she said. • "We don't know how to control it yet. We don't know why they've recently come to apples." —Art Agnello A simple trap baited with ethyl alcohol (vodka will work) can be