| dc.description.abstract | After its discovery in North America during the summer of 2000, the soybean
aphid, Aphis glycines Matsumura (Hemiptera: Aphididae) became a major pest of the
soybean, Glycine max (L.) Merr., in most soybean growing regions of the United States.
The use of insect-resistant plant varieties and natural enemies, important components of
Integrated Pest Management (IPM), when applied solely have the potential to be effective
measures for controlling soybean aphids. However, resistant host plants may influence
natural enemies in beneficial or detrimental ways, thereby altering their effectiveness when
the two strategies are combined. Therefore, we investigated how a resistant variety impacts
fitness of a biological control agent to understand its compatibility for pest management of
the soybean aphid. A near isogenic susceptible soybean variety without the Ragl gene and
a resistant variety with the Ragl gene were used to determine the effect of the Ragl on the
development and fitness of the soybean aphid parasitoid, Binodoxys communis Gahan
(Hymenoptera: Braconidae). Before testing for effects of the Ragl gene on the parasitoid,
we first validated the expression of the Ragl gene and confirmed that these plants were
resistant to soybean aphids by determining the growth rate of soybean aphids on both
resistant and susceptible plants. The soybean aphid population and per capita growth rate
were significantly higher when reared on susceptible soybean plants compared to resistant
plants. In addition, polymerase chain reaction (PCR) was used to verify the genotypes and
the presence of the Ragl gene in some of the plants used in the growth rate experiment. Results of the soybean aphid growth rate experiment combined with the results of the PCR
helped to validate the expression of the Raglin the resistant plants used in our
experiments. To determine the impact of these resistant plants on parasitoids, the total
numbers of mummies (parasitized soybean aphids) produced and adult parasitoid
emergence were compared for parasitoids that were given aphid hosts from either
susceptible or resistant plants. Parasitoid fitness was measured in terms of parasitoid
development time, their body length, and their metatibiae length. We found a higher
number of mummies in susceptible soybean plants than in the resistant plants as well as a
higher emergence rate of adult parasitoids from the mummies reared on susceptible plants.
The development time from mummy to adult parasitoid emergence was only one day
longer with aphid hosts from resistant plants compared to susceptible plants. Despite some
difference in the size of parasitoids from resistant and susceptible plants, very few
parasitoids completed development on resistant plants. In summary, our results indicate
poorer establishment and reproductive performance of B. communis from soybean aphids
on resistant plants compared to soybean aphids on susceptible plants. This suggests that
widespread adoption of resistant soybean plants might be detrimental to the overall
sustainability of this parasitoid and its ability to help control soybean aphids. We did,
however, find that at least some B. communis could successfully develop and emerge on
soybean aphids from resistant plants, suggesting that there is at least some possibility that
the parasitoid could survive and assist in aphid management even if the Rag 1 resistant
plants become commonplace. The parasitoid's relative fitness and reproductive output will
likely play important roles in ultimately determining the short- and long-term compatibility
of utilizing both B. communis and resistant soybean plants for soybean aphid control. | en_US |
