The other major guild of insects that feed on plants include galling insects. Feeding by the immatures of these insects in the early developmental stages of plants or plant parts modifies plant phenotype to develop galls. Such structures provide the insect with a safe feeding site that also acts as a nutrient sink in the plant. The Hessian fly, a common pest of wheat across the globe, is an example of galling insects.
The signs of Hessian fly infestation on wheat plants are not easily identifiable except for the death of plants causing bare or sparse patches in the areas of heavy infestation. In some cases, they cause lodging of tillers and darker bluish color of the leaves (Fig. 11) (Whitworth et al. 2010, Schmid et al. in press). These symptoms may be identifiable in images taken by a low flying UAV. Subsequent field surveys could verify the prevalence of pest infestation in the field and help developing management practices.
Similar UAV and remote sensing methods as described above are applicable for mapping infestation by gall forming insects in the field. Poor performance of plants because of pest infestation can be identified in a field based on lower NDVI values. In the cases of the Hessian fly infestation on wheat, we demonstrated a significant negative relationship between NDVI and pest infestation (Bhattarai et al. in prep). NDVI estimated from both the satellite (Sentinel 2 [LINK]) and manned-aircraft (TerrAvion[LINK]) data decreased with increasing Hessian fly infestation in the commercial wheat fields in Kansas. Although multi- and hyper-spectral data are expected to detect unusually darker foliage of the Hessian fly infested plants in the field evidence for such pattern does not exist.
Bhattarai, GP, RB Schmid, and BP McCornack. in prep. Detecting insect pests in agricultural fields using remote sensing data
Schmid, R. B., A. E. Knutson, K. L. Giles, and B. P. McCornack. in press. Hessian fly (Diptera: Cecidomyiidae) biology and management in wheat
Whitworth, R. J., P. E. Sloderbeck, and H. N. Davis. 2010. Crop insects in Kansas. Kansas State University
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