Controlling Two Aquatic Plant Pests: China Mark Moth, Nymphuliella daeckealis (Haimbach) and the Waterlily Leafcutter, Synclita obliteralis (Walker)
Significance of These Pests in Ornamental Ponds
The increasing popularity of aquatic gardens has created a strong demand for high- quality aquatic plant material. Unfortunately, insect pests can damage these aquatic plants. Maryland nursery and landscape managers report that two major insect pests commonly damage waterlilies: the China mark moth, Nymphuliella daeckealis (Haimbach), Family Crambidae, Nymphulinae, and a waterlily leafcutter, Synclita obliteralis (Walker), another Crambidae. Aquatic nurseries and landscape companies have limited options for controlling these insect pests in aquatic pools.
Feeding injury from N. daeckealis and waterlily leafcutter larvae causes aquatic plant producers major economic losses. In aquatic landscapes, damage from larval feeding makes plants unattractive, and excessive populations may reduce plant vigor or cause plant death.
Little information has been published about the life cycles of these two aquatic plant pests. To address this problem, University of Maryland Extension faculty at the Central Maryland Research and Education Center and at College Park conducted studies, detailed below, to establish basic life cycle information about N. daeckealis.
Life Cycle of N. daeckealis in Maryland
Egg and Larval Stages
Adult females lay eggs close to the edge of the waterlily leaf or on the leaf’s underside. After the eggs hatch, the larvae begin cutting small shot holes, which vary in diameter from 0.25 inch (63 cm) to 0.75 inch (1.8 cm), on the edge of the foliage. The larvae use the cutout leaf pieces as a body covering that serves as protection and enables the larvae to float.
N. daeckealis larvae have four instars, based on head capsule measurements. The moths overwinter as late instar larvae attached to the underwater stems of aquatic plants. In the spring, the water begins to warm and new waterlily foliage moves toward the surface. The larva, enclosed between two pieces of leaf held together with silk, begins to migrate to the water surface to feed on foliage. The larva attaches to the underside or edge of the leaf or moves to the leaf blade where feeding results in leaf skeletonization. Throughout development, the larva uses two cutout leaf pieces to construct an enclosed, boat-like, floating structure, and places itself between these pieces, forming a case. The larva then spins a silken layer inside the case. This case provides protection and transportation, allowing larvae to float from plant to plant. As the larva progresses through the instars, it consumes leaf tissue while concealed within the cut piece of foliage. As the larva matures, it harvests new, larger leaf pieces. The late instar leaf casing will be 0.5 inch to 0.75 inch (1.27 cm to 1.9 cm) long. When the larva in its case comes in contact with a waterlily leaf, the larva attaches itself and begins to feed.
Whereas early instar larvae are skeletonizers, late instar larvae are defoliators, consuming the entire leaf tissue. The larva does not leave the leaf case. If you carefully extract larvae from their leaf cases and place them in the aquatic pool, they sink and die. The leaf casing, therefore, appears to be essential to larva survival.
During hot weather, larvae were observed in higher numbers than during cool, rainy weather. During the later instars, larvae were found migrating over the leaf surface covered by a cut leaf piece and then boring down into the waterlily leaf petiole from the top of the leaf. Larvae often join whole waterlily leaves together and feed between the leaves. Cocoons can be found on the underside of leaves and attached to the stem.
The insect’s development continues until cooler temperatures arrive and the water- lily foliage becomes scarce. At this time, remaining late instar larvae migrate down the waterlily leaf stem and overwinter inside their leaf boat.
