Effect of Metaldehyde on Survival, Enzyme Activities, and Histopathology of the Apple Snail Pomacea canaliculata (Lamarck 1822)

Abstract

Pomacea canaliculata, as an invasive exotic species in Asia, can adversely affect crop yields, eco-environment, and human health. Application of molluscicides containing metaldehyde is one effective method for controlling P. canaliculata. In order to investigate the effects of metaldehyde on adult snails, we conducted acute toxicological experiments to investigate the changes in enzyme activities and histopathology after 24 h and 48 h of metaldehyde action. The results showed that the median lethal concentrations (LC) of metaldehyde on P. canaliculata were 3.792, 2.195, 1.833, and 1.706 mg/L at exposure times of 24, 48, 72, and 96 h, respectively. Treatment and time significantly affected acetylcholinesterase (AChE), glutathione S-transferase (GST), and total antioxidant capacity (TAC) activity, with sex significantly affecting AChE, GST, and TAC activity and time significantly affecting carboxylesterase (CarE). In addition, the interaction of treatment and time significantly affected the activity of GST, CarE and TAC. In addition, histopathological changes occurred in the digestive glands, gills and gastropods of apple snail exposed to metaldehyde. Histological examination of the digestive glands included atrophy of the digestive cells, widening of the hemolymph gap, and an increase in basophils. In treated snails, the hemolymph gap in the gills was widely dilated, the columnar cells were disorganized or even necrotic, and the columnar muscle cells in the ventral foot were loosely arranged and the muscle fibers reduced. The findings of this study can provide some references for controlling the toxicity mechanism of invasive species.

Keywords: acute toxicity; digestive gland; histopathology; molluscicide.

Figure 1

Effect of sublethal concentrations of metaldehyde on the enzymatic activities of AChE, GST, CarE and TAC in the digestive gland of P. canaliculata. CK indicates control; data are expressed as mean ± SE.

Figure 2

Micrographs of P. canaliculata digestive glands. (A). Digestive glands of control snails showing digestive cells (dc), basophils (bc), tubular lumen (T), and dark granules (dg). (D,E). digestive glands were exposed to 1/2 LC₅₀ metaldehyde. (B,C). Digestive glands exposed to 1/4 LC₅₀ metaldehyde show a widening of the hemolymph gap and an increase in basophils.

Figure 3

Micrographs of the gills of P. canaliculata. (A). In details of gill filaments of control group snails, normal gill filament columnar cells (CC) are tightly arranged, a few mucous cells (MC) are visible, and the hemolysis gap (h) is narrow. (D,E). Gill filaments exposed to 1/2 LC₅₀ of metaldehyde show disorganized gill filament columnar cells (CC) with cell degeneration, cilia loss (blue arrows), a greatly expanded hemolysis gap (h), and inflammatory cell infiltration (i). (B,C). Gill filaments exposed to 1/4 LC₅₀ metaldehyde show slight loosening and degenerative arrangement of gill filament columnar epithelial cells (CC) and more area of hemolysis gap expansion (h).

Figure 4

Micrographs of the ventral foot of P. canaliculata. (A). The ventral foot of the control group snails shows a neat and orderly arrangement of epithelial cells (e), normal morphology of columnar muscle cells (cm), and an interlocking arrangement of muscle fibers. (D,E). The ventral foot of the snail exposed to 1/2 LC₅₀ metaldehyde shows degeneration, necrosis, and an indistinct morphology of the epithelial cells (e) of the ventral foot. Columnar muscle cells (cm) were loosely arranged and scattered, with a marked reduction in myofibers and scattered interstitial inflammatory cell infiltration (i). (B,C). The ventral foot of snails exposed to 1/4 LC₅₀ metaldehyde shows varying degrees of inflammatory cell infiltration visible between fibers (i).