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Host Specificity of the Ragwort Seed FY1,2

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Seneca Jacobi L. is a poisonous weed that is rapidly spreading along the Pacific coast. In an effort to control this plant biologically the ragwort seed fly, Hy lemma (Pegohylemyia) Seneca ella (Meade), was selected for study from among the insects attacking ragwort. It is univoltine, and opposition in nature is very closely synchronized with the formation of the flower buds of its biennial host plant. The eggs are normally placed under the calyx bracts of the unopened buds, alongside the young florets. The larvae feed on the seeds about I month and drop to the ground to pupate when mature.

In our opposition tests, no eggs were laid on the buds of 32 species or varieties of plants in the Composite, including lettuce, Lacuna saliva var. capita's L.; safflower, Cardamoms tinctures L.; chicory, Ci thorium intybus L. and 4 species of Senecio. Small numbers of eggs were laid on the buds of Senecio vulgaris L., S. cineraria DC., Cota tinctoria (L.) Gay, Chrysanthemum segetum L., Erigeron canadensis (L.) Cronq., Calendula sp., and Cichorium endivia L. These eggs either failed to hatch, or the larvae failed to complete their development, apparently because of abnormal placement of the eggs, chemical unsuitability of the host, and/or the opening of the flower head before larval development was completed. The number of eggs deposited on the Senecio species tested was in direct proportion to their phylogenetic proximity and morphological similarity to S. jacobaea. On the basis of these host specificity studies, the seed fly has now been approved for release against S. jacobaea.

Document Type: Research Article

Publication date: April 1, 1967

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  • Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.
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