INVESTIGADORES
BUTELER micaela
congresos y reuniones científicas
Título:
Temporal variation and cultivar effects on wheat stem sawfly larval mortality
Autor/es:
BUTELER, M.; D. K. WEAVER; PETERSON, R.K
Lugar:
Indianapolis, USA
Reunión:
Conferencia; Reunion Anual de la Sociedad Entomologica de Estados Unidos; 2009
Institución organizadora:
Entomological Society of America
Resumen:
The larval idiobionts Bracon cephi and B. lissogaster (Hymenoptera: Braconidae), parasitize the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), in wheat in Montana. These parasitoids prevent future damage by killing the sawfly larvae and they also prevent yield loss associated with larval sawfly feeding (Buteler et al. 2008, Agric. For. Entomol. 10: 347-354; 11: 123). These solitary ectoparasitoids attack their hosts by inserting their ovipositor through the stem wall to sting and paralyze the  larvae. The parasitoid larvae feed on the sawfly larvae (Fig. 1a) and pupate within a cocoon inside the stems (Fig. 1b). Adults chew a hole in the stem from which they emerge (Fig. 1c). These braconid parasitoids are bivoltine, and the second generation overwinters in the wheat stubble. Thus, postharvest residue management is critical  to survival of the overwintering cocoons, and leaving tall undisturbed residue is recommended (Runyon et al. 2002, J. Econ. Entomol. 95: 1130-1134). Crops that senesce later probably experience greater rates of parasitism by providing more time for oviposition by second generation adults.  There is limited information on the performance of these parasitoids in newer wheat cultivars, and the historical literature are rom Canadian populations of B. cephi only. The study was conducted in two wheat fields, one near Conrad and the other near Havre, Montana, separated by a distance of approx. 165 km. Each large field had a history of sawfly parasitism and were planted with two different spring wheat cultivars.  In Havre, where overall parasitism is lower than in Conrad, earlier maturing solid stem wheat had lower proportions of parasitized larvae before harvest. In proportions of parasitized larvae in Conrad, both types of wheat had similar numbers (Fig. 2).Wheat in Conrad senesced later, and was harvested around two weeks later than in Havre both years of the study. This may explain the greater parasitism levels for both cultivars found in Conrad.  It is likely that wheat harvested later had greater parasitism because it serves as a sink for oviposition by later second generation adults. After harvest, even though there was typically a greater number of sawfly hosts in the solid stemmed wheat, both types of cultivars had relatively similar number of surviving parasitoids within a site/year (Fig. 3).  The success of second generation adults at parasitizing overwintering larvae was typically low (Fig. 4), but it was generally greater in later maturing hollow stem wheat than in earlier maturing solid stem wheat.Overall, these data suggest that solid stem wheat is similar in suitability to hollow stem wheat for parasitoids, although later maturing hollow stem cultivars can yield greater numbers of parasitized larvae late in the season. The study was conducted in two wheat fields, one near Conrad and the other near Havre, Montana, separated by a distance of approx. 165 km. Each large field had a history of sawfly parasitism and were planted with two different spring wheat cultivars.  In Havre, where overall parasitism is lower than in Conrad, earlier maturing solid stem wheat had lower proportions of parasitized larvae before harvest. In proportions of parasitized larvae in Conrad, both types of wheat had similar numbers (Fig. 2).Wheat in Conrad senesced later, and was harvested around two weeks later than in Havre both years of the study. This may explain the greater parasitism levels for both cultivars found in Conrad.  It is likely that wheat harvested later had greater parasitism because it serves as a sink for oviposition by later second generation adults. After harvest, even though there was typically a greater number of sawfly hosts in the solid stemmed wheat, both types of cultivars had relatively similar number of surviving parasitoids within a site/year (Fig. 3).  The success of second generation adults at parasitizing overwintering larvae was typically low (Fig. 4), but it was generally greater in later maturing hollow stem wheat than in earlier maturing solid stem wheat.Overall, these data suggest that solid stem wheat is similar in suitability to hollow stem wheat for parasitoids, although later maturing hollow stem cultivars can yield greater numbers of parasitized larvae late in the season. The study was conducted in two wheat fields, one near Conrad and the other near Havre, Montana, separated by a distance of approx. 165 km. Each large field had a history of sawfly parasitism and were planted with two different spring wheat cultivars.  In Havre, where overall parasitism is lower than in Conrad, earlier maturing solid stem wheat had lower proportions of parasitized larvae before harvest. In proportions of parasitized larvae in Conrad, both types of wheat had similar numbers (Fig. 2).Wheat in Conrad senesced later, and was harvested around two weeks later than in Havre both years of the study. This may explain the greater parasitism levels for both cultivars found in Conrad.  It is likely that wheat harvested later had greater parasitism because it serves as a sink for oviposition by later second generation adults. After harvest, even though there was typically a greater number of sawfly hosts in the solid stemmed wheat, both types of cultivars had relatively similar number of surviving parasitoids within a site/year (Fig. 3).  The success of second generation adults at parasitizing overwintering larvae was typically low (Fig. 4), but it was generally greater in later maturing hollow stem wheat than in earlier maturing solid stem wheat.Overall, these data suggest that solid stem wheat is similar in suitability to hollow stem wheat for parasitoids, although later maturing hollow stem cultivars can yield greater numbers of parasitized larvae late in the season.
rds']