Bedellia orchilella Walsingham Lepidoptera Lyonetiidae

Natural History

Distribution. Morningglory leafminer apparently is a native to Eurasia, but now it is widely distributed in the United States. Morningglory leafminer likely occurs in southern Canada but it is not recorded as a pest there. It is found in most areas of the world, including both tropical and temperate climates. Sweet-potato leafminer is associated with sweet potato in Hawaii, but its origin is uncertain, and it does not occur elsewhere in the United States or Canada.

Host Plants. Larvae of both species feed on plants in the family Convolvulaceae. Among vegetables, only sweet potato is attacked. Wild hosts include bindweed, Convolvulus spp., and morningglory, Ipomoea spp.

Natural Enemies. Morningglory leafminer is frequently parasitized by Apanteles bedelliae Viereck (Hymenoptera: Braconidae). Also reared from mor-ningglory leafminer is Spilochalcis albifrons Walsh (Hymenoptera: Chalcididae), but there is some disagreement whether this wasp is a primary parasite or hyperparasite.

A parasitoid identified as Omphale metallicus Ash-mead (Hymenoptera: Eulophidae) attacks sweetpotato leafminer. In Hawaii this parasitoid is thought to be a significant mortality factor; nevertheless, leafminer can be a serious problem in the absence of insecticides. Apanteles bedelliae was introduced to Hawaii to aid in suppression of sweetpotato leafminer, and is reported to be effective (Zimmerman, 1978).

Life Cycle and Description. These species are similar, though because there are some differences in their biology they are treated separately.

In morningglory leafminer, total development time, from the egg to adult stage, requires about 30 days at 18°C, but only 16-17 days at 29°C. Two generations are reported annually in New York.

  1. The eggs of morningglory leafminer are described as translucent white and a flattened sphere in shape. They measure about 0.3 mm long and 0.2 mm wide. Eggs generally are deposited on the lower surface of leaves, and usually adjacent to leaf veins. They are placed singly or in small clusters of 2-3 eggs. Embryonic development requires about 4.5 days at 27°C.
  2. Upon hatching, larvae of morningglory leafminer burrow directly into the leaf tissue. They are yellowish-gray though they turn greenish with age. Larvae develop dorsal pink spots during the third instar which disappear in the fourth instar, and are replaced by reddish tubercles in the fourth and fifth instars. White tubercles are added during the fifth instar. First instar larvae appear to be legless, but both thoracic legs and prolegs are evident in subsequent instars. Head capsule widths are 0.09, 0.15, 0.22, 0.31, and 0.45 mm in instars 1-5, respectively. Larvae are somewhat flattened in appearance and the anal prolegs project posteriorly, forming a fork. The first two instars form serpentine mines, but young third instars leave the mine, construct a lose webbing of silk on the lower surface of the leaf, and re-enter the leaf tissue to form a blotch-like mine. The remaining instars also function as blotch miners. An interesting feature of the feeding behavior is that except while molting the larvae use the silk as a point of attachment while feeding, insert the anterior portion of their body into the mine but leave the posterior portion protruding from the mine. At this point the larva voids its fecal material externally. The larva usually forms several blotch mines during its development. Fecal material is voided from the blotch and usually hangs down in a continuously webbed chain. Larval development time is about 11 days at 27°C. (See color figure 91.)
  3. Newly formed pupae are greenish with a mottled-red pattern but the red gradually fades and the pupae become greenish or brownish. The posterior end of the pupa is anchored to silk webbing. The anterior end is also supported by silk threads, however, so the pupa is positioned parallel to the leaf rather than hanging from the substrate by its anal end. Duration of the pupal stage is about 4.5 days at 27°C.
  4. Adults of morningglory leafminer are grayish brown and with fringed wings. The wingspan is about 11.5 mm. Females begin ovipositing soon after mating and deposit about 170 eggs (range 80-324 eggs). Most eggs are laid about 1-8 days after oviposi-tion commences, at about 20 eggs per day. Longevity of adults is about 25 days.

Sweetpotato leafminer is a relatively unimportant pest on a minor crop. Thus, it is perhaps not surprising that little about this insect is known, and that phenology is undocumented. As is the case with morning-glory leaf miner, a complete generation requires about 30 days. In Hawaii, it likely occurs whenever its host is available.

  1. The eggs of sweetpotato leafminer are laid singly in a crevice along a vein, usually on the lower surface of a leaf. The eggs are oval and flattened, and measure 0.3 by 0.2 mm in size. In color the eggs are whitish to reddish and highly iridescent. Duration of the egg stage is about eight days.
  2. The larval stage of sweetpotato leafminer is small, growing from about 0.4 mm to 7.0 mm long as it matures. The larva tunnels between the upper and lower leaf surfaces as it feeds. The tunnels are quite long and narrow, unlike morningglory leafminer where the mine becomes blotch-like as the larva reaches maturity. As the food supply is exhausted the larva leave its tunnel for a new feeding position and creates a new tunnel. When not in the tunnel the larva moves with a looping motion. The caterpillar is greenish throughout its development, and unlike many Lepidoptera the head, prothoracic and anal shield are not darkly pigmented, though they may have a brownish tint. Moderately sized hairs are sparsely distributed on the body. Duration of the larval stage is about 10 days.

Sweetpotato leafminer larva.

Sweetpotato leafminer larva.

Sweetpotato leafminer pupa.

Sweetpotato leafminer pupa.

  1. When the sweetpotato leafminer larva is mature it leaves the mine and spins a few silken strands which are used to anchor the pupa to the outside of the leaf. The pupa is dark-green when first formed, assuming a brown color with black spots as it matures. The head bears a dark angular projection, and the eyes are black. The pupa measures about 3.5 mm long. Duration of the pupal stage is about six days.
  2. The moth of sweetpotato leafminer is grayish-brown, and lacks distinctive markings. The wings, however, are unusual in form. The forewing tapers to a point distally, and the trailing edge bears a long fringe. The hind wing is very narrow, but bears a fringe of long hairs on all sides. The wingspan of the moth is about 7.5 mm.

Morningglory leafminer was described by Shorey and Anderson (1960) and Parrella and Kok (1977). Biology of this species in Egypt seems to be nearly identical (Tawfik et al., 1976). Clemens (1862) gave a good description of the larvae. Biology of sweetpotato leafminer was described by Fullaway (1911); Zimmerman (1978) added useful observations.

Adult sweetpotato leafminer.

Damage

The larvae of both species mine the foliage of sweet potato, leaving long-winding tunnels containing fecal material. As noted earlier, the larva of mor-ningglory leafminer changes its behavior and forms blotch mines later in life. If infestations are heavy the leaves acquire a withered or seared appearance. Sweet potato is quite tolerant of foliar injury, so leafminers is not usually considered to be a serious pest. Parrella and Kok (1977) suggested that hot weather was unfavorable for survival of morningglory leafmi-ner, which might explain why it rarely was reported to be damaging.

Management

Foliar insecticides, particularly systemic materials, can be applied for leaf miner suppression. Except perhaps in Hawaii, these species are rarely abundant, and insecticide applications are used sparingly so as not to disrupt naturally occurring parasitoids.

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