Southern Pine Beetle Biological Control

Dendroctonus frontalis Zimmermann
Scolytidae

From: Frank, J. Howard and John L. Foltz, 1997, Classical Biological Control of Pest Insects of Trees in the Southern United States: A Review and Recommendations, USDA, FS, FHTET-96-20.

Native: AL, AR, FL, GA, KY, LA, MS, NC, SC, TN, VA, WV, eastern OK and TX, and parts of Mexico and Honduras.

Resident natural enemies: Anthocoridae: Scoloposcelis mississippensis Drake and Harris -- NC. Cleridae: Thanasimus dubius (F.) -- GA, LA, MS, NC, TX (with hyperparasitoid Baryscapus thanasimi (Ashmead)). Braconidae: Atanycolus comosifrons Shenefelt -- FL, LA, MS, NC, TX and North; Cenocoelius nigrisoma (Rohwer) -- GA, LA, MS, NC, SC, TX; Coeloides pissodis (Ashmead) -- GA, LA, MS, NC, TX and North; Dendroster sulcatus Muesebeck -- Fl, GA, NC, TX and North; Doryctes anatolokus Marsh -- FL and North; Ecphylus schwarzii (Ashmead) -- NC and North, Meteorus hypophloei Cushman -- FL, GA, LA, MS, NC, TX and West; Spathius canadensis Ashmead -- NC, VA, and North; S. pallidus Ashmead -- GA, LA, MS, NC, TX and North; Vipio rugator (Say) -- FL, TX, and North. Ichneumonidae: Cremastus sp. -- NC. Torymidae: Roptrocerus xylophagorum (Ratzeburg) (= R. eccoptogastri) -- GA, LA, MS, NC, TX, VA, WV and North and West, Pteromalidae: Dinotiscus dendroctoni (Ashmead) (= Cecidostiba dendroctoni) -- GA, NC, TX, VA, WV, and West; Heydenia unica Cook and Davis GA, AL, NC, VA, WV and North and West. Eurytomidae: Eurytoma cleri (Ashmead) -- GA, NC, VA, WV, and West; E. conica Provancher -- not in South; E. tomici Ashmead -- GA, LA, MS, TX, VA. Scelionidae: Gryon sp. -- LA; Idris sp. -- LA; Leptoteleia sp. -- NC; Probaryconus heidemanni Ashmead -- GA, TX, VA.

Biological control attempts: Thanasimus formicarius (L.) (Cleridae) from Germany was released in WV (2,200 individuals) in 1892-1894, but was not recovered (Hopkins 1893). Some 200 individuals of the same species, from the USSR, were released in MS in 1980, and again was not recovered (Miller et al. 1987). Individuals of Rhizophagus grandis Gyllenhal (Rhizophagidae) from Europe were imported into the United States in 1976-1977, but were not released (Miller et al. 1987). These few North American attempts to establish biological control agents of foreign origin were trival in view of the importance of D. frontalis as a pest. Westward spread of Dendroctonus micans (Kugelann) in Europe led to programs in several western European countries to culture, release, and establish Rhizophagus grandis Gyllenhal from farther east in the pest's range (Evans and King 1989, Gregoire et al. 1989). Preliminary analysis of the results in reports of the British Forestry Commission is encouraging (e.g. Fielding 1992).

Biological control possibilities: Rhizophagus grandis (see under Dendroctonus terebrans) offers some possibilities. Natural enemies of D. frontalis in the disjunct parts of its range in Mexico (e.g., Tejada and Patton 1979) and Central America are too poorly known to determine whether any of them might serve as a biological control agent for importation into the South. The literature shows a general problem in documentation of natural enemies of scolytids (Conopthorus, Corthylus, Dendroctonus, Ips, Scolytus, Xylosandrus, and Xyleborus). Part of the problem was caused by inadequacy of systematics of scolytids and of their natural enemieswhen work was begun many decades ago. Consequently, there are no records of natural enemies for some species, whereas for other species there are long lists of records, some of them of questionable validity.

Another part of the problem was caused by recording of some organisms as natural enemies simply because they were discovered "in association" with scolytids, whereas they may inflict little or no mortality on scolytids. For this reason, it is necessary to set aside all early records that cannot be substantiated by existing voucher specimens of both the pest and its natural enemey (either parasitoid or predator) accompanied by adequate documentation. Consequently, we did not bother to copy all the records of natural enemies that we found in the literature. To resolve the problem we recommend (a) collecting voucher specimens of natural enemies of scolytids (accompanied by the scolytid specimen which was the host of a parasitoid or the prey of a predator) from every state, and (b) compiling a computerized database of records. Specimens of organisms that were collected "in associaton" with a scolytid would also be housed, and data about them would be entered into the database. One of the fields in the database would be reserved for direct evidence of causation of mortality, and another would be reserved for estimates of proportion of mortality inflicted on a pest population by the organism in question at numerous geographical locations. Data accompanying voucher specimens now housed in the U.S. National Museum of Natural History could be integrated into the database after reexamination of the specimens.

These recommedations would be inexpensive to carry out because they should take only a small part of the time of one professional entomologist who has an interest in systematics. Until these actions are taken, the predator-prey and host-parasitoid associations will remain unclear, and the potential for classical biological control will remain obscure.

Collaboration with forestry services in Canada and Mexico in constructing the database, in sharing taxonomic expertise, and in exchanging voucher specimens, is highly desirable. Dendroctonus frontalis is a prime example. There may be natural enemies in Mexico or Central America that could become useful as biological control agents for the South, but knowledge of the natural enemy complex in the South is fuzzy, and knowledge of the natural enemy complex in Mexico and Central America is almost nonexistent.

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