Progress 09/15/02 to 09/14/05
Outputs
Research was conducted to elucidate the biology of palm leaf skeletonizers, including Homaledra sabalella (Lepidoptera: Coleophoridae), which is native to Florida and the Caribbean and has long been known on some palmate palms, and a putative cryptic species of Homaledra that is believed to be a relatively recent adventive in Florida, Puerto Rico, and the US Virgin Islands, and that infests primarily coconut palms, Cocos nucifera. No external taxonomic characters were observed to distinguish between Homaledra sabalella and Homaledra sp., but slight internal differences were found. Near the end of the current project, we initiated but have not yet completed molecular studies to clarify the taxonomy of Homaledra spp. In the field, we presently distinguish these species by their host plants. In a survey, Homaledra sabalella was found from southern Florida to Savannah, Georgia. In field studies, larvae of H. sabalella matured in about 20-35 days, attaining a maximum mean
length of 15.0 mm. The larvae fed on the superficial tissues of the abaxial, and less commonly the adaxial leaf surface, constructing tubes of silk and frass in which they remained concealed. A technique was developed using a lamp to illuminate the tubes and observe larval activity. The larvae fed and constructed sections of their tubes at night, and were inactive during the day. The nightly increase in tube length was about 3 mm, and the mean length of the tube at the completion of the larval stage was 74 mm (range, 32-112 mm). On some nights, the larvae shifted the positions of their tubes to occupy fresh leaf tissue. When mature, the larvae formed a cocoon by drawing the tubes into a ball. The pupal stage was completed in 14-16 days (27 degrees C constant temperature). Based on monthly sampling of Homaledra sp. on coconut palm in Puerto Rico and Florida, population fluctuations showed no consistent seasonal pattern. Caterpillars of Homaledra spp. were observed on 78 species of
palms. In a field test in Florida, bifenthrin applied as a foliar spray killed 100 percent of Homaledra sabalella larvae on Sabal palmetto and Latania loddigesii. In Puerto Rico, 100 percent of Homaledra sp. larvae were killed by feeding on bifenthrin-treated palm leaf material in the laboratory, but in the field there was a high percentage survival of larvae on palms treated with bifenthrin. Natural enemies of Homaledra spp. included hymenopterous parasitoids of diverse families. Phytomyptera sp. n.(Diptera: Tachinidae) was the most frequent and widespread parasitoid reared from Homaledra sabalella and Homaledra sp. in Florida. This species was possibly introduced along with Homaledra sp. in Florida and may be a major factor in a reduction in recent years of palm leaf skeletonizer damage there. It was not collected in Puerto Rico in spite of intensive collecting and rearing efforts. The more extensive damage to palms by Homaledra spp. in Puerto Rico compared to Florida may be related
to the absence of Phytomyptera on this island. This tachinid should be studied as a potential biological control agent for introduction into Puerto Rico and possibly California for control of Homaledra spp.
Impacts
The knowledge of bionomics of palm leaf skeletonizers generated in this project is useful as a basis for developing and improving pest management practices for these and related insect pests. The chemical control methods developed in the project will be of use for management of the pest, including quarantine and regulatory efforts. Knowledge of the natural enemies of these pests is essential to the development of biological control.
Publications
- No publications reported this period
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Progress 10/01/03 to 09/30/04
Outputs
Observations were continued to elucidate the biology of the palm leaf skeletonizer, Homaledra sabalella (Chambers), and a putative cryptic species of Homaledra. The former is native to Florida and the western Caribbean and is usually a minor pest of cabbage palmetto, Sabal palmetto, and other palmate palms. Beginning in the 1990s, outbreaks of a species of Homaledra were observed in Florida, Puerto Rico, and the U.S. Virgin Islands, causing severe damage, especially to coconut palms, Cocos nucifera. Since H. sabalella had rarely been observed on coconut palm, it was hypothesized that this was an introduced cryptic species of this genus. After intensive examination, no external taxonomic characters were observed to distinguish between Homaledra sabalella and the putative new species, but slight differences were observed in the morphology of the male genitalia. In the late 1990s, a palm leaf skeletonizer identified as Homaledra sabalella was found on palms in southern
California. We are conducting studies using DNA technology to clarify the taxonomy of these species of Homaledra in Florida and the Caribbean, and determine which of the species is present in Southern California. In studies in the field, larvae of H. sabalella developed to the pupal stage in about 20-35 days, attaining a maximum mean length of 15.0 mm. The larvae fed on the superficial tissues of the abaxial, and less commonly the adaxial leaf surface, constructing tubes of silk and frass in which they remained concealed. They fed, and increased the lengths of their tubes at night, and apparently were inactive during the day. The nightly increase in tube length was about 3 mm, and the mean length of the tube at the completion of the larval stage was 74 mm (range, 32-112 mm). The larvae formed a cocoon by drawing the tubes into a ball. The pupal stage was completed in 14 -16 days (observations at 27 degrees C constant temperature). Data are being analyzed from monthly sampling to
determine the seasonal distribution of Homaledra sp. Palms were examined on various sites including natural and urban areas, and arboreta and botanical gardens. Homaledra spp. were observed on 60 species of palms. Bifenthrin was tested as a foliar spray for control of Homaledra sp. on Sabal palmetto and Latania loddigesii. In both tests, this treatment resulted in 100 percent mortality of the caterpillars. Biological control would be the best long range management method. Natural enemies of Homaledra spp. were reported last year, at which time Phytomyptera n. sp. (Diptera: Tachinidae) was found to be the predominant natural enemy of both Homaledra sabalella and the putative new species in southern Florida. During observations this year, the same species of Phytomyptera was found to parasitize Homaledra sabalella in northern Florida near Gainesville, extending the known range of this species, which had previously been thought to be restricted to the tropical climate of southern
Florida. This finding implies that Phytomyptera is well adapted to both tropical and cooler regions where Homaledra spp. is present, which would be an advantage for this potential biocontrol agent in some areas.
Impacts
The knowledge of bionomics of palm leaf skeletonizers generated in this project is useful as a basis for developing and improving pest management practices for these and related insect pests. An understanding of the seasonal history will provide a basis for timing chemical and other methods of control, and knowledge of the natural enemies of these pests is essential to the development of biological control.
Publications
- Howard, F. W., and R. M. Giblin-Davis 2004. Palm insects. pp. 1622-1627, In John Capinera (ed.), Encyclopedia of Entomology, Vol.3.. Kluwer Academic Publishers, Dordrecht, the Netherlands.
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Progress 10/01/02 to 10/01/03
Outputs
Studies are being conducted to elucidate the bionomics of Homaledra sabalella (Lepidoptera: Coleophoridae), and the closely related Homaledra sp. n. in Florida, Puerto Rico, and the U.S. Virgin Islands. Both species are palm leaf skeletonizers. Homaledra sabalella is native to Florida and islands of the western Caribbean. It attacks several species of palms, but is most common on Sabal spp. and other fan-leaf palms. Homaledra sp. n. is apparently an introduced species in Florida and Puerto Rico, and is found most often on coconut palm, Cocos nucifera. The caterpillars of Homaledra spp. prefer mature rather than young leaves. Caterpillars of Homaledra sp. n. were seldom found on leaves of coconut younger than 4 months. In Florida, the numbers of caterpillars of Homaledra sp. n. on coconut palms diminished during the summer season. However, in Puerto Rico, numbers of Homaledra-damaged areas on foliage increased in summer. Sampling methods for both regions will be
standardized for future comparisons. In a survey of natural enemies of Homaledra spp., a total of 230 specimens of Hymenoptera and 263 specimens of Diptera were reared from caterpillars in Florida. Phytomyptera sp. n. (Diptera: Tachinidae) was the most widespread parasitoid reared from both species of Homaledra. Hymenoptera included Conura sp. (Chalcidae), Horismenus sp. nr. ignotus (Eulophidae), Arachnophaga costalis, Brasema sp. (Eupelmidae), Goniozus nigrifemur, G. scitulus (Bethylidae), and an unidentified genus and species of Scelionidae. A predatory beetle, Plochinus amandus (Coleoptera: Carabidae) was found in tubelike shelters made by the caterpillars on leaves. There were similarities and differences in the natural enemy complex attacking Homaledra spp. in Puerto Rico and in Florida. Conura sp. (Chalcidae) was found in both regions. Additional specimens reared from Homaledra spp. in Puerto Rico were identified to the families or superfamilies Bethylidae, Braconidae,
Chalcidoidea, Elasmidae, and Eupelmidae. Specimens of these and from the U.S. Virgin Islands are being processed for identification to species. Only one species of Diptera, i.e. a species of Syrphidae, was identified as a natural enemy of Homaledra sp. in Puerto Rico. Phytomyptera sp. n. (Tachinidae) has not been reared from Homaledra spp. in Puerto Rico. It is noteworthy that damage to palms by Homaledra spp. is currently more extensive in Puerto Rico than in Florida. Possibly this may be related to the absence of Phytomyptera, which is so prominent in Florida. This tachinid should be studied as a potential biological control agent for introduction into Puerto Rico, and possibly California.
Impacts
The knowledge of bionomics of palm leaf skeletonizers generated in this project is useful as a basis for developing and improving pest management practices for these and related insect pests. An understanding of the seasonal history will provide a basis for timing chemical and other methods of control, and knowledge of the natural enemies of these pests is essential to the development of biological control.
Publications
- No publications reported this period
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