Morphological description of the white grub Melolontha incana (Coleoptera: Scarabaeidae: Melolonthinae: Melolonthini)

Abstract

Melolonthinae are the largest subfamily of Scarabaeidae, considered as serious pests for their larvae attacking plant roots and tubers. The edaphic larvae are difficult to be identified because the study on larval taxonomy is far from satisfactory. In this study, multivoltine white grubs Melolontha incana (Motschulsky, 1853) were investigated using light and scanning electron microscopy, in order to provide more morphological characters for the pest identification. The white grubs are atypical for the epipharynx bearing 14 heli arranged in two rows; the mandible is furnished with a patch of minute granules; the maxilla is equipped with 18 acute stridulatory teeth arranged in line; each femur and tibiotarsus is furnished ventrally with a cluster of fossorial setae. The morphological comparisons with the other melolonthine species were provided. The adaptative relationship between the morphological feature and the multivoltine life history were briefly discussed.

Morphology of a grass‐feeding white grub Apogonia cupreoviridis (Coleoptera: Scarabaeidae: Melolonthinae: Diplotaxini) using scanning electron microscopy

“…However, during our field collections and observations on A. cupreoviridis , the adults feed on gramineous grasses and fallen ginkgo leaves, while the larvae were rarely observed in the farmland. These phenomena are quite different from the contribal Liogenys fusca (Rodrigues, Fuhrmann, et al, 2017) and most of the other crop‐feeding white grubs in Melolonthinae (Jia et al, 2020, 2021; Zhang, 1984).…”

“…The larvae usually possess seven short sensilla basiconica in Cetoniinae (Dong et al, 2020), eight sensilla basiconica in some Rutelinae (Fang et al, 2018); five short sensilla basiconica and a long sensillum trichodeum in some Aphodiinae (Li et al, 2019); and none in Prismognathus dauricus (Lucanidae) (Qu et al, 2019). In Melolonthinae, the larval antennae have 11 sensilla basiconica in Melolontha melolontha (Eilers et al, 2012) and M. incana (Jia et al, 2021), 21 sensilla basiconica in Pseudosymmachia tumidifrons , and 26 in Brahmina faldermanni (Jia et al, 2020). In this study, the larva of A. cupreoviridis is remarkably furnished with one bifurcated sensilla and nine basiconic sensilla on the antennal apex.…”

“…The arrangements of palidia on raster vary greatly in Melolonthinae (Hayes, 1929; Ritcher, 1966; Zhang, 1984). The palidia consist of a single, transverse, slightly curved, com‐like row of flattened pali anterior to the ventral anal lobes in Sericini (Pardo‐Locarno et al, 2007; Šípek & Ahrens, 2011), two parallel rows in Pseudosymmachia (Jia et al, 2020) and Melolontha incana (Jia et al, 2021), distally divergent in some Brahmina (Jia et al, 2020), circular, convergent at both ends in some Macrodactylini (Lugo‐García et al, 2018; Neita‐Moreno et al, 2012) and absent in some Holotrichia and other species (Zhang, 1984). In the current study, the palidia of A. cupreoviridis consist of two rows of pali arranged in V‐shape, similar to the previously described species in Diplotaxini (Table 1), although the number of pali is quite different (Ferreira et al, 2018; Patil & Veeresh, 1984; Rodrigues, Fuhrmann, et al, 2017).…”

“…For scanning electron microscopy (SEM), a total number of 10 fixed larvae were serially dehydrated in a graded ethanol (80%, 90%, 95%, 100%, and 100%) for 30 min each, then replaced by the graded mixtures of ethanol and tertiary butanol (3:1, 1:1 and 1:3, v/v) for 15 min and pure tertiary butanol for 30 min twice. After freeze-dried for over 2 h, the samples were sputter-coated with gold, and examined under a Hitachi S-3400N scanning electron microscope (Hitachi) at 5 kV, following the method using in Jia et al (2021).…”

“…In fact, larvae of Melolonthinae play complex roles in agricultural ecosystems, consuming decayed materials, feeding on weeds in farmlands, or even serving as prey or hosts for other animals and microbes (East & Pottinger, 1975; Sushil et al, 2008). Despite economic and ecological significance, larvae of Melolonthinae have been described for only 59 species, mainly belonged to Melolonthini, Rhizotrogini, Sericini, Macrodacylini, Pachydemini, Hoplini and some Diplotaxini (Jia et al, 2020, 2021; Neita‐Moreno et al, 2012; Ritcher, 1966; Sanmartin, 2007; Sawada, 1991; Šípek & Ahrens, 2011; Zhang, 1984).…”