 |
Diana Pilson University of Nebraska dpilson1@unl.edu |
|
|
Diana Pilson University of Nebraska dpilson1@unl.edu |
Five species of moth commonly feed within wild sunflower inflorescences at our field site, representing five genera: Suleima, Homoeosoma, Cochylis, Isophrictis, and Plagiomimicus. The first three may occur as pests on crop sunflower as well.
 |
 |
| Suleima helianthana | Empty pupal case and larval frass on bud |
Two generations per year are seen at our field site. The first generation larvae develop in the stems of growing plants. By the time these larvae have pupated, wild sunflower inflorescences have begun to appear. The first generation lays their eggs on the developing buds, where the larvae develop. Larvae in stems can cause malformation of the plant, including loss of the main stem and the development of multiple side branches. Larvae in buds appear to malform the inflorescence as well, and many damaged buds probably do not flower.
 |
 |
 |
|
Adult P. spumosum
|
Larva just entering...
|
Late instar P. spumosum
|
Adults of this moth are nocturnal and rarely seen, although the larvae are common in most years at our site. Early instar larvae can be found under the petals of unopened buds, and later larvae tunnel into the back of the flowerhead through a puddle of plant exudate. Larvae enter the flowerhead anywhere from 10 days before to 5 days after the inflorescence opens. The larval entrance hole is readily visible as the larva continues to push dark frass (larval excrement) out, creating a frass pile embedded in the sap. Several larvae may enter a flowerhead, but only 1 larva usually survives to pupation due to intraspecific predation. Larvae are equally aggressive in the lab, and must be isolated in separate containers. Larvae feed on developing achenes and hollow out a space under the seeds. Feeding by Plagiomimicus often damages >50% of the seeds in a head.
 |
 |
|
Larva exposed
in “bald” area of eaten seeds (florets removed)
|
Multiple
entrance holes with frass
on back of inflorescence |
Larvae of this species are dark with lighter longitudinal stripes, and can easily be found on wild sunflower heads because of their telltale webbing. Larvae initially feed on pollen, and are recorded to feed on crop sunflower achenes. In wild inflorescences, the larvae appear to tunnel among, and feed upon, developing achenes. Individual flowerheads (diameter ~18mm) have contained nearly 30 larvae. Larvae are also highly mobile and move between flowers and probably between plants, as the larvae are common hanging on the field crew after a day in the plots.
 |
 |
|
Typical H.
electellum larva
on an inflorescence |
Webbing produced |
 |
 |
|
Isophrictis
adult
|
Probable
seed damage by Isophrictis sp.
|
|
|
|
Isophrictis
sp. larvae
|
Larval
holes in dried receptacle
|
Isophrictis larvae appear to feed within an individual achene in early instars. Later instars, pupae, and empty pupal cases are common in the drying receptacle of flowerheads that are beginning that are releasing seeds. Several larvae and/or pupae may be found in a flowerhead.
 |
 |
 |
| Cochylis hospes larvae | Seeds damaged by Cochylis hospes | Adult Cochylis |
The larvae of this moth vary from pink to bright green, and are found in webbing among the florets. They feed on achenes from this webbing, and thus leave a characteristic hole on the top of damaged seeds.
 |
 |