PROGRESS REPORT~~SFRI SOUTHERN FOREST RESEARCH INSTITUTE

PUBLISHED Bl-MONTHLY

JANUARY - FEBRUARY 1972 UNDER INVESTIGATION-

Thanasimus dubius-an Important Predator of the Southern Pine Beetle

Among the insect enemies of the southern pine beetle, Thanasimus dubius may not always be the most abundant; howeve,:-, this clerid beetle is the most obvious predator and very likely a most effective one. Good reasons ex.ist for making this assumption: both adults and larvae are predacious and decimate all stages of their prey from the egg to the full_y grown beetle. Furthermore, the pred­ ators maintain an amazing degree of spacial and temporal coincidence with their prey, and particularly so with southern pine be~tle populations. These observations are not new. In fact, early investi­ gators gave considerable attention to the clerid predators as potential control agents of the southern pine beetle. The species also has an T. dubius feeding on a important dictinction. In southern pine beetle 1892, A. D. Hopkins imported about 2,000 specimen of the European species Thanasimus formicarius from Germany for re­ lease in West Virginia. The insects failed to become established, but this effort now marks a historical event: the first importation of a predator into the United States for the biological control of a forest insect. In another early report published in 1908, W. F. Fiske reported in the proceedings of the Entomological Society of Washington, D. C. (p. 23-27) that it was not uncommon to find southern pine beetle infested trees in which the brood had been largely destroyed by T. dubius. He assumed that clerid predators were capable of reducing epidemic levels of their prey species but undertook no specific investigations. R. C. Thatcher and L. S. Pickard (J. Econ. Entomol. 59: 955-957 .1966) first reported the much needed information on the biology and habits of T. dubius. We now know that the clerid may have 2½ to 4 generations annually in the Gulf Coast region versus 6 to 8 for the southern pine beetle. Studies reveal that the adult predator, during a life span of 5-10 weeks, destroys at least 75 southern pine beetles under experimental conditions. Similarly, a single predator larva may destroy more than 100 immature stages of the bark beetle. However, both are probably less effective under field conditions since they must search for the prey before feeding begins. The adult predators are extremely active and intercept many attacking beetles before they bore into the bark. "In the field, the life cycles of T. dubius and the south­ ern pine beetle were found to be closely synchronized at the be­ ginning of an attack. As the southern pine beetles landed on the bark, the adults of T. dubius moved about rapidly catching and feeding upon them and mating and laying eggs." Numerically speaking, the laboratory experiments show that at least 15 clerids were necessary per 100 southern pine beetles to prevent attack on caged bolts. Clerid larva (15x) -2- In 1968, the discovery of frontalin as the attractant of the southern pine beetle by SFRI scientists revealed the amazing phenomenon which allows the predators to arrive simultaneously with their prey on newly infested pine trees. The secret was simple. The predators, in their search for food and mates, use the same odorous clues as their prey. Employing synthetic frontalin, SFRI re­ searchers experimentally demonstrated that T. du­ bius pursues olfactorily the aggregation of the southern pine beetles and intercepts the prey dur­ ing the short period of ambulant life (J. Insect Physiol. 16:233-239. 1970). This demonstration of the spontaneous re­ Mid-stage larva of T. dubius coin­ sponses of both sexes of T. dubius to the attrac­ cides with last stage of southern tant of the southern pine beetle exerted an impor­ pine beetle (2x). tant bearing on contemporary control strategies. It disclosed that control procedures using insecticides on felled pine trees infested with the southern pine beetle inadvertently became more effective against the insect enemies of the pest than against the pest itself because the felled trees con­ tinued to attract predators and parasites following application of the insecticide. (J. Econ. En­ tomol. 64:1440-1444. 1971). On the other hand, the manipulation of an important predator with attractants became a distinct possibility. This, in turn, prompted SFRI scientists to en­ deavor to clarify a number of questions relating to the potential manipulation of T. dubius populations. Two questions in particular arise: What is the actual impact of T. dubius populations on the population dynamics of the southern pine beetle? And, what is the impact of associated in­ sects on the predator population itself? There is no doubt that T. dubius can and does contribute to a decline in southern pine beetle populations; the question remains as to the degree of effec­ tiveness exerted by the predator. Are the predators actually capable of achieving, by themselves, a major reduction of the pest? Some entomologists argue that T. dubius cannot be a highly efficient biological control agent for the southern pine beetle because its life cycle appears poorly synchronized with the prey, and because the clerid diverts its activities to other bark beetle species and is preyed upon by insects such as Temnochila uirescens. As a matter of argument, the life cycle and behavior of T. dubius could also be considered extremely well synchronized with that of the southern pine beetle because their longer life span makes their predation more efficient. The adults of pest and predators arrive on the same tree simultaneously and deposit their eggs. The predators remain to attack the adult pests as long as the pests continue to arrive on the trees and follow the pests to new host trees. The young predator larvae feed on the eggs and young larvae of the pest species while the mid-stage and older predator larvae attack fully grown larvae, pupae and cal­ low adults of the pest. Termination of the feeding period of the predator larvae coincides with the emergence of the south­ ern pine beetle brood. In fact, the predator goes through the non-feeding stages of its development only in the absence of the southern pine beetle. Therefore, of necessity the larval de­ velopment of the clerid surpasses that of the prey by several weeks, and one predator generation roughly covers two pest generations. Furthermore, a model of the predator/prey rela­ tionship may show that the T. dubius populations compensate the developmental delay extremely well through their larger biomass, their prolonged span of adult life, and their reproduc­ tive capacity which is approximately tenfold that of the south­ ern pine beetle. Similarly, it could be argued that the existence of alternative prey species such as fps spp. is rather advan­ tageous for sustaining endemic predator populations and will not hinder the effectiveness of the predator on southern pine Temnochila virescens (4x) beetles unless they become overly distractive. -3- 229 North Bowie Street JASPER, TEXAS 75951 SFRI

SOUTHERN FOREST RESEARCH · INSTITUTE

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This appears unlikely, as present SFRI sponsored studies indicate that none of the various pheromones recently isolated and identified from lps grandicollis and lps calligraphus provide the efficiency in attracting T. dubius as does frontalin. The clerid shows some preference, how­ ever, for trans-verbenol, a pheromone released by a large variety df bark beetle species in contact with fresh, resinous host material. This likely provides a clue as to secondary sources of food for the clerids in the absence of the favored prey species. SFRI investigators began using frontalin baited sticky traps in 1969 to study population trends in the southern pine beetle and the effectiveness of such traps for population surveys. They were immediately impressed with the large proportion of T. dubius captured by the traps when compared with the number of southern pine beetles (Figure). As a possible measure of their impact on the pest population, the following trend becomes evident. Clerid populations remained high during 1969 at a time when the southern pine beetle epidemic appeared to col­ lapse. Predator numbers continued at high levels through the spring of 1970 while the pest - population declined rapidly. Subsequently, the predator population-declined- drastically, and the pest species began a steady increase. Figure - Relative numbers of southern pine beetles (SPB) and its clerid predator, T. dubius, caught on frontalin % baited survey traps during spring (Sp), summer (Su), fall (F), and winter (W) 1969-1971 [n=111,349]. 100 0 ------o SPB . J) ... "" * PREDATOR* I "" * I '°O, I I "'"'O }I ,,, ,,, 75 I * o~--- ~~~if 60 45 >( X\, :\ ~ I • / 1c 30 0 • , -----* ... ,, , '\ 15 •., , * 0

Sp Su F w Sp Su F w Sp Su w [ 1969 ][ 1970 ][ 1971 ]

PROGRESS REPORT, 229 N. Bowie, Jasper, Texas 75951 Jan/Feb 1972 -4- PUBLICATIONS ON SFRI SPONSORED PROJECTS AND RELATED RESEARCH - 1971 (II)

J. P. Vite and J. A. A. Renwick. Inhibition of Dendroctonus frontalis response to frontalin by isomers of brevicomin. Naturwiss. 58:418. 1971.

The olfactory response of flying male and female southern pine beetles, Dendrocto­ nus frontalis Zimm., to the female-produced attractant, frontalin, was inhibited under field conditions by an analogue, endo-brevicomin. Tests in the forest demonstrated that the at­ traction of D. frontalis to traps baited with frontalin and alpha-pinene was halted or dras­ tically reduced, but the response of its predator, Thanasimus dubius F., was unaffected by the addition of this material. (See: SFRI PROGRESS REPORT 1971:9-10.)

J. P. Vite and J. A. A. Renwick. Population aggregating pheromone in the bark beetle, lps grandicollis. J. Insect. Physiol. 17:1699-1704. 1971.

Males and females of the bark beetle, Ips grandicollis, aggregate on host material in response to 2-methyl-6-methylene-7-octen-4-ol, a pheromone characteristic for five-spined fps species. This compound is produced by the male beetle upon feeding in the phloem tissue of suitable pine trees. Other compounds such as trans-verbenol and host ,!erpenes may cause occasional response to pines infested by other bark beetle species.-:----

D. L. Williamson. Olfactory discernment of prey by Medetera bistriata (Diptera:Dolichopodidae). Ann. Entomol. Soc. Am. 64:586-589. 1971.

Attractants, particularly synthetic pheromones of the southern pine beetle, were used to determine the mechanism of prey perception by Medetera bistriata, a dipterous predator. The fly possesses a mechanism capable of deciphering a bouquet of prey-habitat stimuli. A naturally infested tree attracted only one-third as many D. frontalis as did the synthetic compounds, yet M. bistriata response was greatest (87%) to the infested tree stem and a portion of the same tree placed in an olfactometer. This was unlike the response of a clerid predator, Thanasimus dubius, which responded greatest to frontalin. The response behavior of M. bistriata enables it to arrfve simultaneously with more than one prey species. A high degree of synchrony in prey-predator colonization, critical to its survival, is thereby ac­ complished.

SFRI PROGRESS REPORT Mar/Apr 1972 D. L. Williamson and J. P. Vite. Impact of insecticidal control on the southern pine beetle population in east Texas. J. Econ. Entomol. 64:1440-1444. 1971.

Availability of synthetic attractants for the southern pine beetle provided a means to evaluate the effects of prescribed insecticidal control measures on the pest and its natural insect enemies. Chemical communication of the southern pine beetle not only signals its own species for attack on a host, but it also attracts its more important Qredatgrs. Applica­ tion of the insecticidal control technique for southern pine beetle-infested trees inadvertent­ ly becomes more detrimental to beneficial insects than to the target insect for the following reasons:

(1) Secondarily-attracted parasites, predators, and competitors which seek food, mating, and oviposition sites on the outer bark are more efficiently eliminated than the bark beetle brood which is more protected beneath the pine bark. Searching habits of these natural enemies, such as T. dubius, continue longer and over a greater distance than those of the southern pine beetle. Thus, they are more vulnerable to contact with the toxicant.

(2) It was shown that the southern pine beetle exhibits a greater preference for vertical stems than horizontal stems when attacking trees and responding to its attractant. Trees felled and treated with BHC-diesel oil in accordance with recommended procedures con­ tinue to serve as focal points for beetle antagonists which are then decimated by the spray. In contrast, southern pine beetles are triggered to disperse in the absence of attractive centers with vertical host configuration.

(3) A large portion of the target insect population frequently has emerged from trees in an infestation at the time of discovery and treatment. Because of the short generation cycle of 3 to 4 weeks for the southern pinf> t "P.tle, the color of trees often does not fade rapidly enough after an attack to give timely warning. flowever, during optimal develop­ ment of the beetles, the development of important predators lags behind emergence of their prey.

(4) High concentration of insecticides and use of oil-base carriers are necessary to penetrate the thick bark of pine trees. The impact of BHC application on the ecosystem in treated forests may remain debatable; the potential hazards are not At its best, the method lacks lasting effects on southern pine beetle populations. At its worst, the adverse side effects appear to have contributed____.., to the creation of the chronic pest problem in east Texas. PUBLICATIONS ON SFRI SPONSORED PROJECTS AND RELATED RESEARCH - 1971 (I)

J. E. Coster and J. P. Vite. Effects of feeding and mating on pheromone release in the southern pine beetle. Ann. Ent. Soc. Am. 65:263-266. 1972.

Gas chromatographic analysis indicated that females which had fed contained less frontalin and trans-verbenol than similar females that had not fed. The decline in phero­ mone content was not precipitous or abrupt as suggested by behavioral studies with other Dendroctonus. Field bioassays confirmed the gas chromatographic studies in general but showed that in both virgin and mated females peak attractiveness occurred 24-28 hours after the host material was attacked by the beetles. This delay in attractiveness is thought to be due to capture of the attractive principle in frass particles, thus extending the actual decline of production.

G. B. Pitman. trans-Verbenol and alpha-pinene: Their utility in manipulation of the mountain pine beetle. J. Econ. Entomol. 64:426-430. 1971.

During summer 1969, a total of 725 mature white pines were baited with synthetic attractant. The baited trees were distributed over eight 40-acre plots in a grid fashion at approximately 2-chain (=132 ft.) distance from each other. Heavy attack occurred on 133 or 18% of the baited trees and these were eventually killed in spite of their being sprayed to a height of about 20 ft. with a 2.3% solution of lindane prior to baiting. An additional 15% of the baited trees received light attack but only 0.3% of the estimated mature pine in the test area were killed by the beetles. Furthermore, many of these trees were wit~in 10 to 15 ft. of baited, and subsequently mass attacked, pines.

G. B. Pitman and J. P. Vite. Predator-prey response to western pine beetle attractants. J. Econ. Entomol. 64:402-404. 1971.

Sticky traps baited with frontalin caught large numbers of western pine beetle, pre­ dominantly females, and very few predators. In contrast, brevicomin attracted the pest species in moderate numbers, caught mostly males, and a very large number of the predator, Temnochila virescens. It was concluded that it would be undesirable to use brevicomin in a trapping procedure as it destroys large numbers of the predators while exerting little direct effect on the female pest population.

National Science Foundation. It all comes through Columbus. MOSAIC __g_(4):8014. 1971.

Uses an article by J. A. A. Renwick and J. P. Vite in "Nature" on the mechanism of colonization of host trees by the southern pine beetle in response to pheromones as an example for the retrieval of information, through the Office of Science Information Service in Columbus, Ohio.

SFRI PROGRESS REPORT Jan/Feb 1972 J. P. Vite. Silviculture and the management of bark beetle pests. Proc. Tall Timbers Conference on Ecological Animal Control by Habitat Management. ~:155-168. 1971.

Harvest procedures have been and remain an efficient tool in management of bark beetle pests. Used for stand improvement, they work as preventive measures against the build-up of pest population levels that are destructive. Used as control measures, they economically remove pest populations along with the crop and with the least damage to natural enemies of the beetle. These principles of for est management are illustrated in relation to two diverse bark beetles, the spruce engraver, fps typographus L., in Europe and the southern pine beetle, Dendroctonus frontalis Zimmerman, in America. The general trend towards chemical control led to the widespread application of insecticides in an attempt to control bark beetle populations directly. Such attempts met with little success and involved great expense. In Texas, insecticidal control proved more effective against predators than against the pest and very likely caused the chronic outbreak conditions of the southern pine beetle that had never been observed before. The return to harvest control methods coincided with a rapid decline of the high pest population and a remarkable resurgence of insect predators. The recent discovery of population aggrega,ting pheromones led to the first trial imple­ mentation of synthetic bark beetle attractants into silvicultural practices for the manage­ ment of the more serious Dendroctonus pests of pine and Douglas-fir. Particularly, the man­ agement system practiced in southeast Texas is designed to counteract emigration of the southern pine beetle from known locations. The advantage is twofold: fore st management gains time for harvest control and salvage while improved spatial and temporal synchrony between pest and natural enemies intensifies predation as predator and prey respond to the same attractants. Harvest control procedures may best follow silvicultural practices established for the perpetuation of the crop species, but its scheduling must recognize the life cycle and be­ havior of the pest species. This poses more operational complications for one crop species than another.

J. P. Vite. Attractants for control of southern pine beetles. Southern Regional Technical Conference. Soc. Am. For. 1971 :259-265.

Describes "Harvest Control" and "Ground Check Control" of southern pine beetles in East Texas. (See: SFRI PROGRESS REPORT 1971:6-7.)