The Bureau of Entomology has been conducting systematic and economic
investigations of the weevils infesting the bark of the trunk and
terminal shoots of conifers in the United States, the results of which will be
published in the regular technical and popular bulletins ; but since these can not be issued in time to be of service this season, this circular has been prepared to give the information which is of immediate practical importance in regard to one of the most destructive of these weevils

Hopkins, A. D. (Andrew Delmar), 1857-1948

United States. Bureau of Entomology

Undetermined

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0CIRCULAR No. 90. 	 Issued June 18, 1907.United States Department of Agriculture,BUREAU OF ENTOMOLOGY,L. 0. HOWARD, Entomologist and Chief of Bureau.THE WHITE-PINE WEEVIL.'By A. D. HOPKINS,In Charge of Forest Insect Investigations.The Bureau of Entomology has been conducting systematic and eco-nomic investigations of the weevils infesting the bark of the trunk andterminal shoots of conifers in the United States, the results of which will bepublished in the regular technical and popular bulletins ; but sinceC bFIG. 1.—White-pine weevil (Pissocles strobi): a, Adult, smaller figure natural size ; b, larva, line atleft natural length ; c, pupa, small figure of adult showing natural size. (Original )these can not be issued in time to be of service this season, this circularhas been prepared to give the information which is of immediate prac-tical importance in regard to one of the most destructive of these weevils.THE INSECT AND ITS HABITS.The white-pine weevil is a somewhat elongate, brownish snout beetle,4 to 5 mm. in length, having the thorax and elytra marked with irreg-ular spots of brown and white scales (fig. 1, a). The winter is passedin the adult stage, evidently in the ground. The beetles come out oftheir winter quarters and fly early in May, and after feeding for a fewdays on the bark of the living white-pine terminal shoots deposit their1 Pissodes strobi Peck; Order Coleoptera, Family Curculionid.2eggs in punctures in the bark of the shoot of the. previous year's growth,placing one or two eggs in a pit or cavity in the inner bark made bythe beak of the mother beetle. Infrom six to ten days the eggs beginto hatch into small white grubs(larvae), which at first are usuallyfound in large numbers feedingupon the inner bark and cambium(see fig. 2). They usually workdownward and sometimes extendtheir work into the bark of the2-year-old stem and base of thebranches. By the time the larv aehave completed their development(fig. 1, b) they are greatly reducedin numbers by natural enemies andother causes. The survivors bur-row into the wood or pith of theterminal and excavate individualtransformation cells, which theyline and cover with excelsior-likeborings. In these cells they trans-form to pupa (see fig. 1, c) andadults, and during July and Augustof the same year, when the adultsare fully matured, they bore theirway out and seek suitable placesin which to pass the winter.LONG LIFE OF THE ADULT.From recorded observations onsome species of Pissodes or barkweevils by investigators in Europe,and on representatives of otherallied forms in Europe and in thiscountry, it appears that an indi-vidual adult may live two or threeyears and will deposit eggs eachyear.SEASONAL HISTORY.2.—White-pine weevil : Newly hatched larvte 	 The beetles are active from aboutat work in vigorous terminal shoot of white the 1st to the 15th of May or later,pine. (Author's illustration.)depending on local conditions andweather. Eggs are evidently deposited during the principal activity ofthe adults, possibly during the greater part of the month of May. Theaperiod of development of the larvae varies greatly. Those more fortu-nate in securing a continuous food supply may become fully developedbefore some of the less fortunate ones in the same terminal are one-fourth as large, although the eggs from which both came may have beendeposited at about the same time. There is also a wide range in theperiod of transformation to the pupa and adults and again in the emer-gence of the latter. Thus, if the first eggs are deposited about the 8thof May at Milford, Pa., latitude 41° 20', altitude 500 to 1,000 feet, thefirst eggs will begin to hatch about the 14th of May, the first larvae willbe full grown about July 8, the first transformations to the pup willtake place about the 15th of July, the first adults will begin to emergeabout July 25, and adults will continue to come out until the first partof September. Practically all will be out by September 15. The prin-cipal period of emergence, however, is from about the 25th of July tothe middle of August.KINDS OF TREES ATTACKED.The white pine is the tree normally attacked, but the weevil is occa-sionally found in the terminals or topmost branches of the native andcultivated spruces, the jack pine, and very rarely in the pitch pine orother eastern piiies. The attack is confined to the small to large sap-ling and pole stages in the development of the tree.DISTRIBUTION.Our records indicate that this weevil follows the natural range of thewhite pine from southwestern North Carolina into New Brunswick andCanada and westward into Wisconsin.EVIDENCE OF ATTACK.The first evidence of attack on the living terminals is the exudationof fresh, clear, and shining drops of resin. Upon closer examinationfresh pinhole-like punctures are found in the bark (fig. 3), and at thesame time the inconspicuous beetles may be found on the terminal ; butupon the approach of the observer the beetles will often let go theirfoothold and fall to the ground, where they will feign death. In a fewdays after the first attack the injured terminals will have the resinmore or less abundant and conspicuous over the greater part of the sur-face. The first evidence that the terminals are infested with larvae isthe stunted, unhealthy appearance of the young growth at the tip,which will gradually die, the needles turning yellowish and laterbrownish.	 •The time of development of the broods to adults will be indicated bythe first appearance of dead tips.Old work of the weevil is evidenced by the presence of old dead ter-4FIG. 3.—Work of white-pine weevil, showing character of injury, chip cocoons, and pupal cells:a, Vigorous terminal shoot, showing condition of new growth at time pupa are transformingto adults ; b, 3-year-old top, showing how larva have migrated from terminal to the 2 and 3year old internodes ; c, chip cocoon and pupal cell, natural size. (Original.)5minals in the forksof the young trees(fig. 4) , and the re-sults of their workwill be evident in thedeformed growth,large forks, andbroad, low crowns ofboth young and oldtrees (fig. 5) .CHARACTER OF THEDAMAGE.The damage andloss, as affecting thecommercial tree, con-sists not only in thedeath of the terminalshoots, but in subse-quent abnormal de-velopment of thetrees so injured. Thedying of the leadingshoot throws the nextyear's growth into theupper lateral shoots,which results in aforked and m an y-branched top. Eachbranch produces avigorous terminal,and all compete forleadership in formingthe crown. In suc-ceeding years themore vigorous termi-nals of the topmostbranches are at-tacked and killed,causing more branch-es, and thus effec-tually preventing the Fdevelopment of thenormal straight trunkand symmetrical crowI6. 4.—work of white-pine weevil, showing result of killed terminalshoot in 4-year-old top of small sapling. (Original.)n necessary to a tree of commercial value.EXTENT OF DAMAGE.The extent of damage, as affecting natural reproduction, planta-tions, and tim-ber of commer-cial size in theforest, is difficultto estimate ; butit is an impor-tant item to becharged to thelosses in com-mercial growthof white pine andis therefore a for-estry problemwhich must de-mand special at-tention in thefuture manage-ment of wood-lots and forests,wherever the treepredominates.FAVORABLE A N DUNFAVORABLECONDITIONS FORDESTRUCTIVEWORK BY THEWEEVIL.The most fa-vorable condi-tion for seriousinjury by thisweevil consistsin a scattering oropen pure standof young whitepine where thegrowth is healthyand rapid, suchas is found inopen planta-tions, in aban-doned fields, andFPO. 5.—Work of white-pine weevil, showing result of killed terminalshoot in 8-year-old top of large sapling. (Original.) 	 around the bor-ders of dense stands wherever the soil and other conditions are mostfavorable for rapid growth.The unfavorable conditions for injury are slow growth, dense purestands, and mixed stands of pine and hardwood.Under the former conditions the thrifty, vigorous terminals are espe-cially favored as breeding places for the weevil; and where these arekilled, the vital energy of the tree is thrown into the lateral branches.Open stands, therefore, favor the development of large branches and aspreading crown, while under conditions unfavorable to weevil injurythe terminals are smaller and, even if they are killed, the close stand orlateral shade will tend to produce an upward or vertical growth of thetopmost branches, the stronger one taking the lead and soon repairingthe damage.NATURAL ENEMIES.Numerous parasitic and predatory insect enemies attack the develop-ing broods in the terminals. Woodpeckers, also, feed on the maturedFIG. 6.—Barrel for terminal shoots infested by white-pine weevil, with wire screen over end allow-ing escape of parasites but preventing escape of weevils. (Original.)larvae, pupa, and adults. Some of the larvae apparently die fromdisease, and when large numbers of them are crowded together thelarger ones appear to feed on the smaller ones, so that on the averagenot more than from 3 to 5 per cent of the hatched larvw ever reachmaturity and emerge from the infested terminals. However, eachfemale is capable of depositing more than one hundred eggs each yearfor several years ; thus the depredations are continuous. During someyears the damage will be slight, while. in other years it will be verysevere, the amount of injury depending on the number of adults thatsurvive and the conditions presented for their attack and development.METHODS OF CONTROL.It will be seen that in the successful control of this pest, as in thecontrol of forest insects in general, much depends on special features in8the general methods of forest management which will bring aboutunfavorable conditions for injury and thus prevent loss.It will also be seen how important it is to know the principal factsin regard to the life history and habits of the insect, in order to securethe best results from methods of management and of direct control.Heretofore this species has been confused with another species withvery different habits, and some of the published data and recommen-dations based on such confusions are of no value.The white-pine weevil rarely, if ever, passes the winter in the termi-nals. The present evidence indicates that it never breeds in the thickbark on the trunks and stumps of the white pine or other pines ; thusit can not be trapped in the trunks of felled and girdled pine.DESTRUCTION OF THE BROODS.The only practical method of destroying the weevil appears to be thetreatment of the infested terminals, and to secure the best results spe-cial attention must be given to certain important details.If the infested terminals are cut or broken during June and July andburned, the broods of the weevil will be effectually destroyed, but vastnumbers of natural enemies will also be destroyed. A better methodis to collect the terminals during the first half of July before the beetlesbegin to emerge and to place them in tight barrels securely coveredwith wire fly-screen netting on one or both ends (see fig. 6). The bar-rels should be left in the groves, so that the parasites and otherenemies may escape, while the beetles perish. After the 1st of Octoberthe weevils will all be dead, and the netting may then be removed,although the barrels with their contents should be left until the follow-ing June to allow the escape of the later developing and larger parasites.The barrel should not be placed in a position to collect rain. It isnecessary, however, if this method be adopted, that it be repeated twoor three years in succession in the same locality, in order to catch thesuccessive broods from the old parent beetles that live over from pre-ceding years.NOTE.The statements and recommendations in this circular are based on recentobservations and investigations by the author and by Field Assistant W. F. Fiske,and serve as a partial revision of what has hitherto been published.Approved:JAMES WILSON,Secretary of Agriculture.WASHINGTON, D. C., May 21, 1907.0

The white-pine weevil

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The white-pine weevil

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