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Journal of the Lepidopterists' Society
BIOLOGICAL NOTES ON LOXOSTEGE FLORIDALIS (PYRALIDAE)1
John B. Heppner2
Department of Entomology and Nematology, University of Florida, Gainesville, Florida 32611
The genus Loxostege has a worldwide, largely north temperate distribution and includes several economically important species. The sugar beet webworm, Loxostege sticticalis (Linnaeus), is a major Hol-arctic pest, while the garden webworm, L. rantalis (Guenee) is an important North American pest. L. similalis of authors has been incorrectly used in place of the correct name, L. rantalis: the distinct L. similalis (Guenee) is South American (Capps, 1967). Seven species of Loxostege are recorded from Florida (Kimball, 1965).
Loxostege floridalis Barnes & McDunnough (Fig. 1) was described in 1913 as a subspecies of the more widespread L. albiceralis (Grote). E. G. Munroe (pers. comm.) is currently revising the Nearctic Pyralidae and considers L. floridalis to be a distinct species. Barnes & McDunnough (1913) collected larvae of L. floridalis on "Florida cranberry" from "Everglade, Fla." (probably Everglades City, Collier County, Florida). There are no other published records using the common name of "Florida cranberry" but the description provided by Barnes and McDunnough suggests it to be Lycium carolinianum Walter (So-lanaceae), the actual host plant of Loxostege floridalis. The plant is commonly known as Christmas-berry, because of the red fruits on the bushes during December. It is native only to coastal areas in Florida and west to Texas, with a record for coastal South Carolina. Although the host plant is used in inland Florida as an ornamental, L. floridalis has been recorded only from coastal areas in Florida as far north as Titusville on the Atlantic Coast and Cedar Key on the Gulf Coast.
Larvae of L. floridalis collected at Cedar Key were reared in a laboratory in Gainesville, Florida; eggs were not studied.
Larval Biology
Loxostege floridalis has been recorded feeding only on Lycium carolinianum. The related Loxostege albiceralis has been reared in Texas by R. O. Kendall on Lycium carolinianum var. quadrifolium C. L. Hitchie (Munroe, pers. comm.). Loxostege sticticalis is a much more general
1 Florida Agricultural Experiment Station Journal Series No. 5764.
2 Research Associate, Florida State Collection of Arthropods.
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Fig. 1. Adults of Loxostege floridalis: (a) male, dorsal aspect (wing expanse 26 mm); (b) female, dorsal aspect (wing expanse 29 mm) (both from Cedar Key, Levy Co., Fla.: male emerged 24 Jan 74, female emerged 26 May 74).
feeder and has been recorded from a variety of plants (Pepper & Hastings, 1941), three of which are species of Solanaceae. The genus is large and fewer species appear to be as restricted to one host as is L. floridalis.
On 13 December 1973, 12 fifth (last) instar larvae of Loxostege floridalis were found feeding on Lyciam carolinianum at Cedar Key, Levy County, Florida. The larvae were found clustered as a group among several branches, with some silk webbing evident. The communal feeding of L. floridalis is similar to that reported for L. sticticalis larvae (Pepper & Hastings, 1941). On 19 December 1973 only one fifth-ins tar larva was found at the same locality but a number of early second-instar larvae (Fig. 2a) were found clustered on one branch. In the laboratory the larvae of 13 December 1973 became prepupal by 26 December, spun cocoons, and pupated by 2 January 1974. Adults emerged as early as 10 days after pupation. The last-instar larva collected on 19 December 1973, which was subjected to a longer period of natural conditions than the larvae reared in the laboratory, was the only larva to enter diapause after cocoon formation. It was allowed to enter sand, where it constructed an ovate cocoon by 2 January 1974. The cocoon was composed of a thick layer of silk and encrusted with sand particles, making it very stiff and resistant to crushing. The cocoon was 21 mm long, about twice the pupal length. The cocoon had a bulbous apical, hollow chamber that barely became covered by sand
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Fig 2. Larvae of Loxostege floridalis: (a) early 2nd-instars (2x) clustered among leaves of host, Lycium carolinianum; (b) 5th-instar (3x), dorsal aspect (all from Cedar Key, Levy Co., Fla., 19 Dec 73).
when in the substrate and it was separated internally from the main pupal chamber by a thin layer of silk. On 12 May 1974 the cocoon was removed from the sand and found to still contain a prepupal larva, which pupated shortly thereafter, and a female emerged on 26 May (Fig. lb).
Paddock (1912) and Pepper & Hastings (1941) also record substrate cocoon formation for L. sticticalis but the cocoon is about twice the length of the L. floridalis cocoon; very elongate and without a separate, hollow bulbous apical chamber. In both species the apex of the cocoon is just below the substrate surface, although Pepper & Hastings (1941) observed that larvae of L. sticticalis make their cocoons deeper in the substrate during colder weather in Montana. L. rantalis has a cocoon similar to that of L. sticticalis and has similar behavior (Smith & Franklin, 1954). During the winter L. floridalis larvae diapause under natural
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conditions much as L. sticticalis larvae do in the first generation in May. Pepper & Hastings (1941) found a variable percentage of larvae of L. sticticalis from the same egg lots to enter larval diapause in May-June in Montana. The factors that induce larval diapause in some larvae but not in others are not yet known.
Second-instar larvae of L. floridalis collected on 19 December 1973 at Cedar Key molted on 23, 26, and 31 December (only a few were not synchronized), becoming prepupal by 9 January 1974. Of 40 larvae reared about half had spun cocoons in the rearing bags by 11 January 1974, with pupation occurring from 12-21 January. Adults of pupae formed by 12 January emerged on 24 January and sequentially thereafter with an average pupation period of 12.2 days. Pupation periods in L. sticticalis are in the same range of two weeks time in the summer for those larvae not diapausing (Pepper & Hastings, 1941).
Larva
Last-instar larvae of L. floridalis (Fig. 2b) dark gray, with a line of merging yellow spots on either side of midline adjacent to dorso-lateral elevated pinacula. Elevated pinacula become larger on segments nearer head, forming scoli on the dorsum of meso- and metathorax. Pinacula and scoli black, ringed with yellow on integument. Lateral to pinacula, a longitudinal line of merging orange spots margined with yellow. Lower lateral pinacula have integumental yellow bars at bases. Prolegs and venter, gray; thoracic legs, black. Head capsule, orange with most of vertex black, lower frons black, clypeus white, and labrum black. Last-instar larvae 26-32 mm in length.
A more extensive larval description is not included because S. Allyson (Canada Department of Agriculture) is currently preparing detailed larval descriptions for the Nearctic species of Loxostege.
Pupa
Pupa of L. floridalis (Fig. 3-4) yellow-brown with dark brown markings. Most of markings on dorsum of abdomen. Pupae average 11 mm long, 4 mm wide. Head produced to a point apically. Mesothorax moderately convex dorsally, flattened in the center, and prominently divergent from metathorax in lateral aspect (Fig. 4a). All 10 abdominal segments visible; segments 1-8 have similar dark brown marking on each segment (Fig. 3a). Spiracles of abdominal segments 2-3 surrounded by conspicuously dark, heavily sclerotized enlargements of exoskeleton. Setae, sparse. Proleg scars visible on abdominal segments 5-6 ventrally. Cremaster (Fig. 3b) has six posteriorly directed setae and two dorsal recurved hook-like setae. Cremaster of female as illustrated (Figs. 3-4); male cremaster bulbous (twice 9 size) to enclose larger genitalia.
The pupa of L. floridalis is similar morphologically to that of L. sticticalis but the lighter coloration and lack of brown markings in L. sticticalis will distinguish the two species. Pupae of other Loxostege species were not available for comparisons.
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Fig. 3. Pupa, 9, of Loxostege floridalis: (a) dorsal aspect; (b) cremaster, dorsal aspect (Cedar Key, Levy Co., Fla.).
Adult Biology
Nothing has been published on the behavior of adult Loxostege floridalis but inferences can be made from studies of the congeneric species. L. sticticalis is bi vol tine with a larval diapause of up to 10 months, from July until the following May, in Montana (Pepper & Hastings, 1941). Published records of L. floridalis indicate a similar pupation-emergence behavior but a multivoltinism commensurate with the more moderate Florida climate (Kimball, 1965). L. floridalis evidently has four generations in Florida. December larvae become adults during
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1 mm
Fig. 4. Pupa, $, of Loxostege floridalis: (a) lateral aspect; (b) ventral aspect (Cedar Key, Levy Co., Fla.).
January and February except for a percentage of larvae that diapause until May. Although the winter is mild in coastal southern Florida, there is a dry season from mid-winter to June, making diapause useful to insure survival of the population in the event of a particularly dry spring. The second generation of adults emerges in May and the third generation emerges in September. Adults present in November form the fourth generation that produces progeny for the January adults.
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From collections data there appears to be a sequential emergence of adults of L. floridalis to produce adult activity over a longer time period than delineated above for the four generations. A similar emergence overlap is found with L. sticticalis in Montana (Pepper & Hastings, 1941). Available records, however, indicate a lack of adults of L. floridalis from June-August. The voltinism of L. floridalis has not yet been fully studied, but it is possible that a portion of the June larvae do not emerge as adults until November, much as some larvae of the winter generation partially bypass one generation and wait until May to emerge. The remainder of the June larvae may estivate until September rather than emerge after two weeks as in other generations. Such a strategy would be adaptive to insure survival of a portion of the population during adverse conditions such as excessive heat during the summer of any given year.
Acknowledgments
I wish to thank T. C. Emmel, H. N. Greenbaum, and D. H. Habeck, all of the University of Florida, for reading the manuscript. I am also grateful for the information and encouragement given by E. G. Munroe, Biosystematics Research Institute, Agriculture Canada, Ottawa.
Literature Cited
Barnes, W., & J. H. McDunnough. 1913. Contributions to the natural history of the Lepidoptera of North America. 2(4): 166-195, 4 pis.
Capps, H. W. 1967. Review of some species of Loxostege Hiibner and descriptions of new species (Lepidoptera, Pyraustidae: Pyraustinae). Proc. U. S. Nat. Mus. 120: 1-75, 7 pis.
Kimball, C. P. 1965. The Lepidoptera of Florida. An annotated checklist. In Arthropods of Florida and neighboring land areas. Vol. 1. Fla. Dept. Agr., Div. Plant Indus., Gainesville. 363 p., 26 pis.
Paddock, F. B. 1912. The sugar-beet web worm. Loxostege sticticalis Linn. J. Econ. Ent. 5: 436-443.
Pepper, J. H., & E. Hastings. 1941. Life history and control of the sugar-beet webworm Loxostege sticticalis (L.). Mont. Agr. Exp. Stat. Bull. 389: 1-32.
Smith, R. C, & W. W. Franklin. 1954. The garden webworm—Loxostege sim-ilalis Gnen. as an alfalfa pest in Kansas. J. Kan. Ent. Soc. 27: 27-38.