Graduate Thesis Or Dissertation
 

Studies on resistance of rice to Sogatodes oryzicola (Muir) and a parasitoid, Haplogonatopus sp., in Costa Rica

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  • Twenty-one rice cultivars were evaluated to determine the difference between populations of Sogatodes oryzicola (Muir) (Homoptera: Delphacidae) in Costa Rica and Colombia, Survival, mortality and population development of S. oryzicola on five selected cultivars was used to determine levels of plant resistance. The importance and potential of the parasitoid-predator Haplogonatopus sp. (Hymenoptera: Dryinidae) on S. oryzicola also was studied. Minor differences were observed among cultivars: Inti, CICA 4 and IR 8, which were resistant in Colombia were intermediate in Costa Rica. Cultivars rated intermediate in Colombia, were rated the same in Costa Rica, except CR-1113 which was susceptible in two Costa Rica colonies. Susceptible ratings in cultivars coincided in both countries, except Tadukan which was resistant to the Northern Atlantic colony and intermediate in the overall rating in Costa Rica. Seedling mortality in intermediate and resistant cultivars was higher in Colombia. The results indicated that there were no biotypes of S. oryzicola within or between populations in Costa Rica and Colombia. Results suggest that CICA 4 has an antibiotic effect on S. oryzicola : more nymphs died, fewer nymphs were produced and fewer adults developed than on the other cultivars. Longevity of S. oryzicola adults was shorter when they fed on CICA 4, IR 8, CR-1113 or Ciwini than on the susceptible check Bluebonnet 50. Low levels of resistance could explain why rice fields planted with CR-1113 often become infested with S. oryzicola. Haplogonatopus sp. was a parasitoid and predator on S. oryzicola . Percent parasitism ranged from 1.7 to 12.2 in unsprayed plots, and from 1.4 to 5.0 in the sprayed plot. In the laboratory, dryinid females produced ca. 118 offspring. The complete life-cycle of the dryinid was 26.7 +̲ 0.7 days at a mean of 27 C. No dryinid males were found, and females lived 6.8 +̲ 0.8 days. The initial satiation capacity of females was ca. six to seven nymphs with a daily consumption of 15.4 +̲ 0.5 nymphs. S. oryzicola adults were not parasitized or preyed-upon. Second and third instar nymphs were preferred. Winged adults of S. oryzicola (parasitized as fourth and fifth instar nymphs) bearing the parasitoid could be the way this dryinid disperses.
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