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Habitat
and Host Specificity of
Braconid Parasites of Stemborers
(Marianne Alleyne, Claire Rutledge & Robert Wiedenmann)
Since 1994, we have been assessing ecological and physiological suitability and specificity of three species of Old World braconid parasitic wasps. The three species of the Cotesia flavipes-complex attack stemborers that are pests of corn and other gramineous plants; two species are New World stemborers, and the third, European corn borer, is an exotic species.
Cotesia flavipes
(Illustration: Nahum Sauceda)
Parasitic wasps respond to different habitat cues. The three Cotesia species respond differently to odors from different grasses, but differences among grasses were not strongly pronounced. C. flavipes preferred corn and sorghum; C. sesamiae preferred sorghum and wheat; and C. chilonis showed preferences for wheat and giant cane Arundinaria gigantica. C. flavipes and C. sesamiae preferred odors from grasses to non-grasses, whereas C. chilonis showed no preferences for grasses or non-grasses. Further, the wasps did not learn new preferences, meaning they are less likely to switch to new habitats. This habitat specificity ensures the parasites will have little harm to non-target species found outside grass-crop habitats.
Clockwise from Top: Stemborer within tunnel, Female Cotesia wasp inspecting tunnel entrance, Cotesia wasps inspecting host larvae.
We tested host suitability for nine host-parasite associations, using
the braconid parasites Cotesia flavipes, C. sesamiae
and C. chilonis; and the three stemborers, European corn borer
(Ostrinia nubilalis), southwestern corn borer (Diatraea grandiosella)
and sugarcane borer (D. saccharalis). Ostrinia nubilalis
was totally unsuitable for any of the three parasite species. Among the
other six combinations, we found different levels of host immune responses
varying from total suitability (no encapsulation) to total unsuitability
(complete encapsulation), and that the process of encapsulation occurs
at a similar rate, but with differing intermediate steps, among the different
host-parasite combinations.
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Top: Encapsulation cluster as viewed from outside of host. Middle: Heavily encapsulated parasitoid eggs and normal larvae dissected from the same host. Bottom: Encapsulated parasitoid larvae and normal larva dissected from the same host. (M. Alleyne) |
We also imported a South African population of Cotesia sesamiae, to test for compatibility with southwestern corn borer; however, it was physiologically incompatible. Responses to plant cues indicates the parasites should assort themselves into particular habitats in nature, and the physiological specificity expressed indicates that the parasites likely will be able to utilize successfully only a narrow subset of hosts that are encountered in that habitat. Further, the process of encapsulation and its magnitude suggest how we should test physiological suitability for assessing potential biological control agents. Our results on ecological specificity, host suitability and encapsulation show that these parasites will have a narrow ecological and physiological host range, and should have little impact on non-target species, but explicit testing will be needed.
Publications
- Alleyne, M. & R. N. Wiedenmann. 2002. Effect of time in culture on the suitability of two novel-association pyralid hosts for Cotesia sesamiae (Hymenoptera: Braconidae) development. Biological, V25, pp116-122.
- Alleyne, M., R. N. Wiedenmann & R. R. Diaz. 2001. Quantification and development of teratocytes in novel-association host-parasitoid combinations. Journal of Insect Physiology, V47, pp1419-1427.
- Alleyne, M. & R. N. Wiedenmann. 2001. Suitability of lepidopteran stemborers for parasitization by novel-association endoparasitoids. BioControl, V46, pp1-23.
- Alleyne, M. & R. N. Wiedenmann. 2001. Encapsulation and hemocyte numbers in three lepidopteran stemborers parasitized by Cotesia flavipes-complex endoparasitoids. Entomologia Experimentalis et Applicata, V100, pp279-293.
- Alleyne, M. 2001. Physiological factors determining host suitability of lepidopteran stemborers for parasitization by Cotesia flavipes-complex parasitoids (Braconidae: Hymenoptera) Ph.D. Dissertation, Department of Entomology, University of Illinois at Urbana-Champaign.
- Rutledge, C. E. & R. N. Wiedenmann. 1999. Habitat preferences of three congeneric braconid parasitoids: Implications for host-range testing in biological control. Biological Control. 16:144-154.
- Wiedenmann, R. N. & J. W. Smith, Jr. 1999. Using novel host-parasitoid associations for biological control of native pests. Pp. 16-37, in L. D. Charlet and G. J. Brewer, eds. Biological control of native or indigenous insect pests: challenges, constraints and potential. Thomas Say Publications in Entomology.
- Rutledge, C. E. 1998. Habitat preferences and fidelity in the Cotesia flavipes complex (Hymenoptera: Braconidae): Current preferences and the potential for change through learning and selection. Ph.D. Dissertation, Department of Entomology, University of Illinois at Urbana-Champaign.
- Wiedenmann, R. N. 1998. Midwest Institute for Biological Control. Midwest Biological Control News 5:1-2.
- Rutledge, C. E. & R. N. Wiedenmann. 1997. Habitat selection in three closely related parasitoids of stemborers. Midwest Biological Control News 3: 4.
- Smith, J. W., Jr. & R. N. Wiedenmann. 1997. Foraging strategies of stemborer parasites and the application to biological control. Insect Science and its Application 17: 37-49.
- Wiedenmann, R. N. & J. W. Smith, Jr. 1997. Novel associations and importation biological control: the need for ecological and physiological equivalencies. Insect Science and its Application 17: 51-60.