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Local and statewide information on a variety of current topics for home gardeners and market growers.
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Early Season, New Pests - White Lined Sphinx Moth


Lepidopteran (moth/butterfly) larvae seem to be making more than an occasional appearance in 2012. Over the last few weeks, University of Illinois Extension has highlighted local observations of armyworm, yellow-striped armyworm, and variegated cutworms with most of those local observations occurring in Mason and Peoria Counties. While observed larvae did not pose a threat to yield, their numbers were atypically high.

The case in question came into the Mason County office during the last week of May. The client described a grassy area that was covered with thousands of rather large larvae. A field visit found the area littered with numerous green/yellowish green caterpillars. Each individual larva had a single horn on the tail end. Many larvae displayed a prominent yellow line running down either side of the body highlighted by dark "smudgy" borders. Other larvae had a dark-colored back accented by three thin yellow/pale lines. All larvae had five false legs (prolegs). The roughly three-inch caterpillars were crossing a blacktop in droves, seemed to be vacating a weedy conservation area, and were eventually identified as white-lined sphinx moth larvae.

The adult of the white-lined sphinx moth is a very large and very beautiful delta-shaped moth that is highlighted by a mottling of brown, gray, and pink bands. The nectar feeding adult beats its wings much like a hummingbird and is actually mistaken for a hummingbird from time to time. The moth helps transfer pollen and deposits eggs on leaf tissue while visiting plants toward dusk.

Larvae did damage some adjacent corn and some volunteer beans, but they actually seemed rather disinterested in surrounding row crops. Damaged corn seemed to have merely been in the way when hungry larvae passed by. No plants were stripped to the main veins as one might expect when encountering armyworms. Larvae were much more interested in ditch bank weeds and weeds around a nearby homestead. Extension resources from neighboring states note that these larvae love to feed on chickweed, mustards, purslane, etc. Our field visit also noted an affinity for plantains and prostrate knotweeds.

Larvae were likely migrating for two reasons. First, larvae were likely migrating to a new food source following depletion/elimination of their previous food source. Second, larvae were likely also in transit as they prepared to pupate. Our field visit detected several larvae burrowing into the soil – a behavior consistent with the onset of metamorphosis. Larvae will burrow underground a few inches and the resulting pupae will likely seed a second generation of moths and larvae later this season. The two-inch long, brown pupae resulting from that second generation will serve as the overwintering stage.

Could the presence of white-lined sphinx moths indicate a developing issue for crops and produce? A tour of University websites notes that tomatoes, melons, and fruit trees can occasionally suffer injury from these hungry larvae. A review of university websites also noted some observations in Kansas row crop border areas in 2002 which resulted in supplemental (Section 2ee) pesticide labeling. Most available resources indicate that while these larvae may chew on row crops and produce, they will largely ignore crops. Instead the larvae will primarily graze on area weeds. The observation of this insect along with other larvae indicates that a mild southern winter and natural control-deterring dry weather have created a favorable environment for moth/butterfly larvae in 2012.

Matt Montgomery, Extension Educator, University of Illinois Extension, 309-547-3711, mpmontgo@illinois.edu

Here in Livingston, McLean, and Woodford Counties, our proximity to Matt's findings in the Peoria means growers need to be aware of this potential pest issue.  This is a reminder of the importance of field scouting.  Knowing that white lined sphinx larvae are out in large numbers, extra attention should be paid to the development of tomatoes and melons.  Suspected damage or pests found in the field can be brought to our office for diagnosis, or sent to the Digital Diagnostic Lab http://www.dddi.org/uiuc/public/

http://www.dddi.org/uiuc/public/


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