Fenusa pumila Leach, 1817

Zhussip, Mukarram, Akhmetov, Kanat, Burkitbaeva, Ulzhan, Amanova, Gulmaira & Mazhenova, Laura, 2024, Contribution to the diversity of leaf miners of silver birch, Betula pendula Roth in North-Eastern Kazakhstan, Journal of Insect Biodiversity and Systematics 10 (3), pp. 589-604 : 594-596

Fenusa pumila Leach, 1817 ( Figs 3F, 4)

During leaf collection in the Pavlodar Region, 55 mined leaves ( Betula sp. ) were found from the beginning of June to the end of August 2019 –2022 in Pavlodar: Teatralny Public Garden, Victory Public Garden, 3/1 Toraigyrov St.

Occurrence of the leafminer species. Within the territory of the Pavlodar region, this study revealed four species of the genus Stigmella Schrank, 1802 and two species belonging to the genera Phylloporia Heinemann, 1870 and Fenusa Leach, 1817 . During the research, it was found that Stigmella lapponica (Wocke, 1862) and Stigmella naturnella (Klimesch, 1936) were predominant among the six species of miner insects. But if we consider them from the viewpoint of damage to the plant, we can say that Phylloporia bistrigella (Haworth, 1828) and Fenusa pumila Leach, 1817 are more harmful than the other four species (noticeable from the mined leaves). It was noted that most leaf miners belong to the Nepticulidae ( Stigmella species) and constitute 85% of the total diversity of defoliators. This genus is distributed everywhere, in the immediate vicinity of the Irtysh River, and at a distance from it, closer to the central Kazakhstan region (Ekibastuz). The Nepticulidae comprises four species of birch leaf miners in the region. Analyzing the distribution of leaf miners of this taxon, we found that representatives of S. naturnella and S. lapponica were most widespread. These types of leaf miners are found everywhere on birches. The exception is the S. continuella species, which was found only in Pavlodar and was not found in collections of birch leaves in Aksu, Ekibastuz, and the southern and northern areas of the region.

In general, the identified species are characterized by thriving in environments that are rich in trees and confinement to fodder plants of certain species, i.e., monophagy. Potentially harmful pests are S. lapponica , P. bistrigella , and F. pumila because they form a large mine on the leaf blade, in some cases several mines, which leads to plant suppression and defoliation. Fenusa pumila is one of the factors that significantly worsens the condition of silver birch. Unfortunately, chemical treatments are ineffective against these defoliating insects; therefore, further study of these species is required to determine the most effective way to combat them.

Leaf damage. More than 2000 birch leaves were examined in this study, and six species of the Nepticulidae , Incurvariidae , and Tenthredinidae families belonging to three genera were identified in the region: Stigmella , Phylloporia , and Fenusa . Each leaf miner consumes only a relatively small amount of leaf matter during its life; comparing miners with free-living species, one would assume that miners could never cause real damage to trees and plants cultivated by man. However, some species should be treated as separate pests. They appear either in excessive numbers when there are no leaves left on some trees or when they appear very early, which causes significant damage to the development of very young plants. Numerous small lesions accumulate and cause great harm to the development of the infected tree ( Pálsson et al., 2023). Among the examined leaves, 683 were damaged by miners. Hand calculation (the process of performing mathematical operations using only pen and paper, without the aid of electronic devices) was used as the method for counting ( Fig. 5). Many mine characteristics are most easily recognized from a fresh leaf that has not yet had time to dry. The bulk of leaf damage was inflicted by leaf chewers (chewed-off or skeletonized leaves). This type of damage was the only one in A. negundo because leaf mines and galls in this species were recorded in single cases and only during the first and second sampling rounds (in only 1–3 out of 1280–1360 leaves examined). During the third round, the proportion of leaves with mines in B. pendula and S. caprea was 6.2%–6.9% and that of leaves with galls was 0.6%–4.3%. Damages categorized as “other” (leaves with blotches, spots, necrotic areas, etc.) occurred with similar frequencies in all three species. In some cases, it appeared that they were inflicted by leaf-sucking insects or resulted from fungal infection; however, their origin usually remained unclear. The frequencies of such damage in B. pendula ranged between 25–53% during the first sampling round, 67–87% during the second round, and 94–99% during the third round. The total proportion of leaf area removed by the leaf mining proved to differ significantly between tree species (p<0.0001) and between sampling rounds (p<0.0001). On average, this proportion was the lowest in A. negundo (<1% during all rounds), intermediate in B. pendula (5.8% during the third round), and highest in S. caprea (7.5% during the third round). Moreover, the loss of leaf area due to leaf miners markedly increased during the growing season in B. pendula and S. caprea but remained unchanged in A. negundo ( Fig. 6). The seasonal dynamics of this trait in B. pendula and S. caprea and its absence in A. negundo are confirmed by the high statistical significance of the interaction of the factors “tree species” and “sampling round” (p=0.0008). Figure 6 presents the shares of species of each genus from their total number. Figure 4 presents mining insects in the larval stage on birch leaves.