Effect of Gryllotalpa gryllotalpa (Orthoptera: Gryllotalpidae) on plant and crop characteristics of sugar beet, Beta vulgaris L. and detection of associated damage using hyperspectral remote sensing

Sugar beet is considered the most important source of sugar production in Egypt. However, the crop is infested by a wide range of insect pests, which damage the leaves and taproot, leading to substantial yield loss. The mole cricket Gryllotalpa gryllotalpa is one of the insect species causing huge damage to sugar beet and decreasing sugar production. Thus, this study aimed to determine the effect of G. gryllotalpa on the yield, vegetative characteristics, and sugar quality of sugar beet. To achieve this, the reflectance characteristics of sugar beet plants infested by G. gryllotalpa and not infested were analyzed using hyperspectral remote sensing data. These experiments were performed in Al-Qalyubia and El-Fayoum governorates regions, representing Upper and Lower Egypt, during the 2018/2019 season. Sugar beet seedlings of 80 days old were artificially infested by G. gryllotalpa at three intensity levels viz: 5, 10 and 15 adults per replicate. The infestation rate, weight loss, vegetative and sugar quality characteristics were assessed at all levels of G. gryllotalpa infestation. In addition, the damage due to different levels of G. gryllotalpa infestation during three different stages of sugar beet plant growth (the leaf development stage, rosette stage and harvestable stage) was compared using a hyperspectral remote sensing technique. The obtained results demonstrated that percentages of both infestation and weight loss in sugar beet root increased gradually with the increase of G. gryllotalpa infestation level. At the highest infestation level (15 adults/ replicate), the infestation rate reached 45.13% and 56.02% at the Upper and Lower Egypt sites, respectively. At the same locations, the % weight loss was 19.76% and 31.79%, respectively. In both regions, all vegetative characteristics of sugar beet plants such as plant height, number of leaves, and crown diameter were significantly decreased in the plants with different infestation levels comparing with those in the healthy plants. The sucrose and total soluble solids percentages gradually decreased with increasing infestation level. The percentages of sucrose were 17.56%—18.84% at high level of infestation, compared with 20.72% for healthy plants. The results indicated that hyperspectral remote sensing could be effective to distinguish between different infestation levels of G. gryllotalpa. Regarding the spectral bands, their effectiveness was in the following order: blue > green > red > near-infrared. Therefore, the remote sensing techniques could help for detection and prediction of G. gryllotalpa in sugar beet plants.