Recognition of adults
4.5-7.0 mm (male); 6.5-9.0 mm (female)
The anterior male wings are usually dark brown in the basal half and golden in the distal half. The female forewings are more uniform from golden brown to dark brown and the marks are usually less distinct. The labial palps are extremely elongated in both sexes. The males have a front costal fold.
Platynota stultana is similar to other platynota species such as platynota flavedana and rostrana platynota. The anterior costal fold is generally smaller in P. stultana than in these other species. A genital dissection can be used to confirm identity.
Late instar larvae are approximately 12-15 mm long with a cream-colored translucent abdomen. The head and the prothoracic shield are yellowish brown. The posterolateral margins on the prothoracic shield are shaded dark brown in some individuals. An anal comb is present with 5-6 teeth.
Platynota stultana completes 4-6 generations per year. Adults can be present throughout the year for much of their range.
Eggs are placed in masses that contain an average of 97 individual eggs per mass. Newly hatched larvae move to the top of the plant and feed within an outbreak or between two leaves. Young larvae can also be dispersed to other hosts by swelling in the wind with a silk thread. The subsequent instars are fed inside a shelter built with rolled or folded sheets. The larvae complete 5-6 instars in a period of 20-30 days (under greenhouse conditions). Third to fifth installation of last generation of hibernation in reticulated nests. The pupation takes place on a rolled sheet.
The larvae of P. stultana are highly polyphagous and have been recorded feeding on plants in more than 20 families. This species can be a serious pest in greenhouses and vineyards and the economically important hosts include alfalfa, Citrus sp., Corn, cotton, grape, peach, pear and pepper. As P. stultana expanded its range to northern California, it seems that it has also greatly expanded its range of hosts to a wide variety of non-native plants. It is recorded from only a few native plants in California.