Graduate Thesis Or Dissertation
 

Effectiveness of pheromone mating disruption for the ponderosa pine tip moth, Rhyacionia zozana (Kearfott) (Lepidoptera: Tortricidae), and its influence on the associated parasite complex

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  • The importance of pheromones in insect control relies both on their ability to reduce pest populations and on their relatively benign effects on nontarget organisms. This study was conducted to test the effectiveness of a pheromone application for mating disruption of the ponderosa pine tip moth, Rhyacionia zozana (Kearfott), and to determine if this treatment had any affect on the abundance or structure of the associated parasite complex. Chemical analyses, electroantennograms, and field bioassays showed that the most abundant pheromone component for R. zozana was E-9-dodecenyl acetate with a lesser amount of E-9-dodecenol also present. Acetate/alcohol ratios averaged 70:30 in gland washes; male moths were most attracted to sticky traps with synthetic baits containing ratios ranging from 70:30 to 95:5. Sixteen hymenopteran and one dipteran species of parasites were recovered from R. zozana larvae and pupae collected in Calif. and Oreg. Total percentage parasitism was high, averaging 47.2%. The ichneumonid, Glypta zozanae Walley and Barron, was the most abundant parasite, attacking over 30% of the hosts collected. Mastrus aciculatus (Provancher) was second in abundance, accounting for less than 4% parasitism. Hercon laminated-tape dispensers containing synthetic sex pheromone (a 95:5 mixture of E-9-dodecenyl acetate and E-9-dodecenol) were manually applied on 57 ha of ponderosa pine plantations in southern Oreg. The nominal dosage was 13.5 g of pheromone/ha from 100 releasers per hectare spaced at 10 m. Male moth response to pheromone-baited traps and to virgin females showed nearly total disruption of female sex pheromone communication with males. After the mating-disruption application, larval populations were reduced 83.2% in treated areas. The frequency of damaged terminal shoots was 50% lower in pheromone treated plantations than in check plots. Total percentage parasitism was not changed due to the disruption treatment. However, in treated areas, abundances of G. zozanae and M. aciculatus, were reduced and increased, respectively, compared to check plantations. A similarity index showed that the parasite community structures of check and treated areas differed more after disruption than before. Accounting for parasitism and reduced mating, surviving host populations in check plantations were over four times greater than in pheromone disrupted areas. The importance of the host's sex pheromone as a potential kairomone, and effects of changes in the host density caused by the mating disruption treatment on the associated parasites are discussed.
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