UW-Madison/Extension Insect Diagnostic Lab Update May 2, 2024
With the above average temperatures this spring, insect activity is a bit ahead of schedule compared to recent years. Diagnostic caseload at the UW Insect Diagnostic Lab is currently low, but is expected to increase dramatically over the next few weeks. A summary of cases from the UW Insect Diagnostic Lab involving fruit crop insects can be found below:
Spongy moth: We’ve now accumulated enough growing degree days for egg hatch in parts of southern Wisconsin and small caterpillars were recently observed in Walworth and Dane Counties. Expect additional egg hatch in the coming days and activity of “ballooning” caterpillars, which can be dispersed by the wind. Spongy moth populations have been trending upwards for several years due to dry spring weather patterns, and growers with a history of activity and/or an abundance of egg masses should remain vigilant. Growers in northern Wisconsin wanting to get a better idea of the timing of egg hatch can check out the USA Phenology Network’s spongy moth page, with a color-coded forecast map.
Eastern tent caterpillar: Similar to spongy moth, caterpillars have begun emerging in southern parts of the state. Growers should keep an eye out for silken tents and small caterpillars in the coming days and weeks. The USA Phenology Network also has a color-coded forecast map for eastern tent caterpillar. By next week, egg hatch is expected in central Wisconsin.
Scale insects: I’ve recently seen a few samples of oystershell scale and other scale insects at the UW Insect Diagnostic Lab from fruit trees. Since scale insects are covered with a protective waxy coating, it’s important to target to vulnerable juvenile (“crawler”) stages. The timing of crawler activity can vary for each scale species, so properly identifying these insects is an important step. Vigilant scouting during the colder months can also be an important long-term IPM approach as selective pruning and dormant oil treatments can be considerations for managing scale insects.
Spring pollinator activity: As is typical this time of the year, many solitary bees (e.g., mason bees, mining bees, etc.) and other pollinators are active and providing critical ecosystem services. I have recently received many reports of spring pollinator activity from around the state. Use caution when applying pesticides around the time of bloom to reduce risks to pollinators.
Brown marmorated stink bugs: I’ve had a number of reports of adult brown marmorated stink bugs at the UW Insect Diagnostic Lab over the last month. These were mostly from the southern half of the state in residential/structural situations, where overwintering adults were spotted.
Periodical cicadas: This year we’ll experience the emergence of Brood XIII periodical cicadas (Magicicada spp.) which last emerged in parts of southern Wisconsin in 2007 (17 years ago). The distribution of these insects in Wisconsin can be very localized and most growers in the state will not see these insects. However, if you happen to be in a cicada “hotspot”, periodical cicadas can injure both fruit and landscape trees through their egg-laying activities. Historically, damage to fruit trees has been noted in some spots in southern Wisconsin, such as Richland and Walworth Counties.
As of late April and early May, I’ve now received a few reports of cicada tunnels leading to the soil surface from Iowa and Walworth counties. These holes are typically noticed in the soil a few weeks before the mass emergence. Emergence is linked to soil temperatures exceeding 64˚F (18˚C) at a depth of 8 inches. We’ll likely start seeing cicada emergence in late May in Wisconsin with activity continuing into June. Adult cicadas are usually active for around a month, so cicada populations should be on the downswing as July approaches.
See the new Wisconsin Periodical Cicada Website for additional details, including a map of known cicada sites in the state. The site also includes a citizen science project to better document the distribution of these insects in the state. Please consider sharing your sightings and photos of periodical cicadas on that website.
Reminder about diagnostic support from the IDL: Growers and consultants in need of insect diagnostic services are always welcome to submit a sample to the UW Insect Diagnostic Lab. Lab services are provided free of charge. You can find additional information about the IDL here: insectlab.russell.wisc.edu
This article was posted in Insects and tagged Brown Marmorated Stink Bug, eastern tent caterpillar, insect, Insect Diagnostic Lab, periodical cicadas, PJ Liesch, scale insects, spongy moth, spring pollinator activity.