Chionodes mediofuscella (Clemens) (Lepidoptera:Gelechiidae), an indigenous insect infesting the seeds of giant ragweed (Ambrosia trifida L.) (Compositae)

Ragweeds are anemophilic composites belonging to the genus Ambrosia, and are the most important aeroallergens in North America.

Ambrosia trifida L., giant ragweed, is a ruderal plant widely distributed throughout the eastern and central portions of North America. The greatest concentration of this species occurs along the drainage areas bordering the Mississippi and Missouri Rivers. This plant is an annual, and reproduces solely by seeds. These seeds undergo primary and secondary dormancy, and remain viable in the soil for long periods of time.

Conventional forms of control have failed to keep this species in check. Biocontrol by seed-feeding insects may provide a partial solution.

Chionodes mediofuscella (Clemens), a seed-infesting gelechiid, may provide this control in areas where giant ragweed has escaped its natural enemies. The biology and immature stages of this species are poorly known. The egg, last instar, and pupal stadium are described.

Egg: .4-.5 mm in length; greatest width .2 mm. Shape ovoid, obovate, some crescent shaped.

Last instar: length 4-9 mm, head capsule .6-.9 mm in width; weights 1.0-12.0 mg.

Pupa: length 5.2 mm (females), 4.5-4.6 mm (males); thoracic width 1.2-1.4 mm (females), 1.0-1.1 mm (males); abdominal width 1.4-1.8 mm (females), 1.1-1.4 mm (males).

Field collection techniques and methods for rearing the larvae of this species are also described.