Written by Kris Tollerup, University of California Cooperative Extension Area-wide IPM Advisor, Kearney Agricultural Research and Extension Center, Parlier, CA
For a few seasons now, I have been interested in understanding more and ultimately finding better monitoring tools for Leaffooted bug, Leptoglossus spp. Most growers and PCAs have a good working knowledge of this bug and likely have attended one or more of my talks covering the subject. We know that leaffooted bug overwinters in aggregations consisting of just a few to several hundred individuals. The aggregations tend to occur on citrus, palm frowns, Cyprus trees, pomegranate, walnut (Fig. 1), olive, and on/in non-plant substrates like pump houses, farm equipment, and wood piles. The list is extensive. The reason why aggregations can occur on such a diversity of substrates is that they are not necessary interested in feeding but more so in seeking a protected area to survive winter. An interesting behavior that I have made is that aggregations typically occur where the group can best collect heat from the sun during peak solar radiation periods.
In spring or as early as late winter, individuals begin leaving aggregations. I, as well as other researchers, found that dispersion is closely associated with temperature and not necessarily dependent on other environmental factors such as day length. I observed some moderately large aggregations on pomegranate in Tulare Co. and after warm mid-February temperatures of about 80 F, nearly all the LFB dispersed. To particularly where, at that early time in the season, we did not determine. The site had neighboring plantings of citrus and olive, which we surveyed but did not observe LFB in those crops. Typically at mid-March, LFB starts moving into almond and history shows that they can cause substantial economic damage.
Because of work conducted by a host of researchers including, Kent Daane, Kris Tollerup, Brad Higbee, and David Haviland, we have a good understanding of how to manage LFB with insecticides once detected in an orchard (see UC IPM Guidelines for LFB on almond and pistachio). We do not, however have a tool to monitor LFB early in the season when they first begin moving into almond. A handful of University of California and USDA-ARS researchers, including myself are looking at possible lures that could serve to attract LFB to a monitoring trap.
Over the past few years, my team has been working to develop a lure comprised of whole-ground-almond (WGA). We have determined that adult and immature LFB will aggregate on navel orangeworm (NOW) egg traps baited with whole-ground almond. To increase the effectiveness, we modified the NOW egg trap by attaching a 9.75-inch wooden shish kabob skewer to the side which provides a branch-like substrate for LFB egg-laying. The hypothesis is that females will detect a suitable food-source lure and subsequently lay eggs on the trap. Such a trap could detect the early-season movement of LFB into almond via egg-laying.
The UC Pest Management Guidelines recommends monitoring for LFB in almond during March and April by examining aborted nuts for gummosis, or oozing on the nut surface. An important note is that if gummosis is found, it should be distinguished from a physiological disorder by cutting a cross section through the nut and looking for a puncture wound. The drawback, however is that considerable damage can occur before detecting the bug. Additional sampling methods that can be used in April and May include using a beat tray for mid-canopy sampling or a long pole to knock upper-canopy branches to startle adults, causing them to fly. Beat trays provide a useful tool for detecting nymphs but it indicates that adults have been present long enough to lay eggs and for the eggs to hatch. In other words, feeding damage has likely already occurred.
The most effective monitoring method is to be creative. Start by looking for overwintering aggregations around orchards, paying close attention to the proximity of any pomegranate orchards and / or pomegranate hedgerows. If you locate aggregations, note their size and watch them weekly starting at the end of February or early-March to estimate when they begin to disperse. Monitor orchard edges, especially those close to known or possible overwintering sites. Search the sunny side of tree canopies for about 15 to 20 seconds per tree for adult LFB on developed nuts.
Insecticide use should occur only if monitoring indicates the presence of leaffooted bug and/or its feeding damage. Apply insecticides only after considering the potential risks of the compound to beneficial organisms, including bees and biological control agents, and to air or water quality. For more information on these topics please consult the UC IPM Pest Management Guidelines for Almonds.