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Annals of the Entomological Society of America
Oxford University Press on behalf of Entomological Society of America
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Abstract: |
The attraction of entomopathogenic nematodes (EPNs) to herbivore-injured plant roots has been documented
recently to be a common tritrophic interaction. Belowground tritrophic interactions are especially subject
to modulation by many abiotic factors including drought. In this study, complementary greenhouse experiments
were conducted to understand how drought stress might affect a potato plant’s impact on EPN behavior.
In separate trials, the responses of the EPN Steinernema diaprepesi (Nguyen and Duncan) (Rhabditida:
Steinernematidae) to root herbivory by larvae of the weevil Diaprepes abbreviatus (Linnaeus) (Coleoptera:
Curculionidae), in well-watered and drought stressed potato plants, were measured using soil-matrix olfactometers
with two arms. The drought treatments were initiated in 30-d old plants. Drought-stressed potato
plants received water when potentiometers read approximately 20 kPa, while for well-watered plants, the
number was 8 kPa. Four weeks after initiating the treatments, 400 ml water was added to all pots, immediately
before starting the experiments. The experiments revealed that S. diaprepesi infective juveniles (IJs) did
not migrate preferentially toward drought-stressed or well-watered plants when neither were subjected to
herbivory [t(21) = 1.13, P = 0.269]. However, plants with roots damaged by herbivory attracted more S. diaprepesi
IJs if they were well watered than if they were drought stressed [t(24) = 3.19, P = 0.004]. If both plants in the olfactometers
were drought stressed, EPNs moved preferentially toward those with root herbivory than those
with undamaged roots [t(23) = 3.19, P = 0.004]. No difference was detected in gas chromatography profiles
between droughted and well-watered plant roots subjected to herbivory [F(24, 336) = 0.68, P = 0.87]. GC analysis
showed that three compounds, including 3-nonanone [t(6) = 4.83, P = 0.003], artemisyl ketone [t(7) = 6.21,
P = 0.000], and benzoic acid, 4-ethoxy-, ethyl ester [t(7) = −4.22, P = 0.004] were significantly higher in drought
stressed than control plant roots. These results indicate that potatoes, like other plants, can recruit EPNs in response
to root herbivory, and that drought stress dampens this tritrophic interaction where choice is involved.
Additional research that resolves the mechanisms of these interactions may provide insights to exploit EPNs
for crop protection.
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