- ~* 
 
 Issued March 23, 1910. 
 
 I'. S. DEPARTMENT OF AGRICULTURE 
 
 BDREAD OF ENTOMOLOGY CIRCULAR No. 119. 
 
 L. O. \ lOWARD. Entomologist and Chirf of Bureau. 
 
 T1IK CLOVEE ROOT-BORER 
 
 K. M. WEBSTER, 
 
 eal and Forage Tnseci Investigations. 
 
 •ji'.i: Cir mt m 
 
 : .I\TIMG OFFICE : 1910 
 
B UREA U OF ENTOMOLOGY 
 
 L. O. Howard, Entomologist and Chief of Bureau . 
 C. L. Marlatt, Assistant Entomologist and Acting Chief in Absence of Chief. 
 R. S. Clifton, Executive Assistant. 
 Chas. J. Gilliss, ChieJ < lerk. 
 
 F. H. Chittenden 1 , in charge of truck crop and stored product inst ct investigations. 
 
 A. D. Hopkins, in charge of forest insi ct inx stigations. 
 
 \V. D. Hunter, to charge of southern field crop insect investigations. 
 
 F. M. Webster, in charge of cereal and forage insect investigations. 
 
 A . L. Quaintance, in charge of deciduous fruit insect investigations . 
 
 E. F. Phillips, in charge of bee culture. 
 
 I>. M. Rogers, in charge of preventing spread of moths, field work. 
 
 Rolla P. Currie, to charge of editorial ivorl. 
 
 Mabel Colcord, librarian 
 
 Cereal and Forage Insect Investigations 
 
 F. M. Webster, in charg< 
 
 Geo. I. Reeves, YV. J. Phillips, C. N. Ainslie, E. O. G. Kelly, J. A. 
 IFvslop, V. L. Wildermuth, R. A. Vickery, T. II. Parks, Herbert 
 Osborn, agents and experts. 
 [Cir. 110] 
 
 (II). 
 
Circular No. 1 19. 'Revision of Circular No. 67.) 
 
 
 United States Department of Agriculture, 
 
 BUREAU OF ENTOMOLOGY, 
 
 L. O. HOWARD, Entomologist and Chief of Bureau. 
 
 THE CLOVEK ROOT-BORER. 
 
 Hylastinus obscurus Marsham. 
 
 r. , F. M. Webstek, 
 I <'■::■ g, of C> • al and Fora i I I ligations. 
 
 i vri:< )in i i ion. 
 
 The clover root-borer {Hylastinus obscurus Marsham) is not a 
 native of America, bul has been introduced from Europe and lias 
 established itself in the fields of red clover in some sections of the 
 eastern United States, as well as throughout the Stales of Oregon 
 and Washington, wherever clover is grown. Ii frequently commits 
 serious depredations by burrowing in the roots, thereby destroy- 
 ing the plants. It has long been known in Europe as a clover pest, 
 Eichoff" giving its distribution as Germany, Aus- 
 tria, France, England, and the Canary Islands. 
 Other European entomologists have also written 
 of its occurrence, and, according to Bach, it 
 infested large fields of clover near Odenbach> i^^^Ss 
 
 Germany, in 1803, an occurrence evidently coin- 
 cident with its description In Marsham in 1S02. 
 
 While it did not come to notice in America as 
 a pest until about 1S7S, when it was found in 
 destructive abundance in central New York, it 
 probably occurred in this country long prior to 
 that date. Dr. A. D. Hopkins, who is making a Fig. i The clover root- 
 special stn.lv of this group of beetles, riz, the ^f^T? 
 
 r s> l > Adu 1 itural size 
 
 Scolytidae, has shown the writer a specimen, from ai right. (Author's nius- 
 thecoUection of the late Doctor Fitch, with a New " 
 
 York label attached to the pin, referring to a note which he has 1 □ 
 
 unable to find. In all probability, however, this specimen antedates 
 the discovery of the insect by Riley in L878. Besides, owing to the 
 obscure habits of the pest, it is more than likely t hat it w as injurious 
 to clover even prior to this date- without, however, having been 
 detected bj farmers. Even at present, both in the Middle West 
 ami on the Pacific coast, where it is mosl destructive, it has 
 attracted httlc attention, die effects of its ravages being usually 
 
 
 I 'i' I luropai i hen Borkenkafer, p. '■>:, L881. 
 
 (1) 
 
attributed to adverse meteorological conditions. The pest seems 
 to have spread much more rapidly westward than southward, as it 
 probably occurs in the East nearly to the Mississippi River; but it 
 has attracted no attention along the Atlantic coast south of Penn- 
 sylvania. In that State, however, the writer found it abundant around 
 Chambersburg, but not disastrously so, in October, 1905. It has not 
 been reported at all from the vicinit}^ of Washington, D. C. It is cer- 
 tainly not seriously injurious in the New Eng- 
 land States at the present time, the late Dr. 
 James Fletcher reported a similar state of 
 affairs in Ontario, "Canada, and we do not 
 receive any reports of its occurrence between 
 the Mississippi River and the Rocky Mountains. 
 In Ohio, West Virginia, Indiana, and south- 
 ern Michigan it is becoming more and more 
 destructive. 
 
 Fig. 2.— The clover root-borer: 
 Larva or grub. Much en- 
 larged. (Author's illustra- 
 tion.) 
 
 DESCRIPTION OF THE INSECT. 
 
 The fully developed insect is a small, dark- 
 brown, hard-bodied beetle, shown enlarged in figure 1. 
 
 The larva, or grub, shown enlarged in figure 2, is about an eighth 
 of an inch long, dingy white, with honey-yellow head and brown jaws. 
 
 The pupa (fig. 3) is even smaller than the larva, also dingy white, 
 with two minute spinous projections on the top of the head and two 
 somewhat larger ones at the anal extremity. The eggs are elliptical, 
 white, and minute, yet large enough to be seen with the unaided eye. 
 
 LIFE HISTORY. 
 
 In the East there is certainly but one generation annually, though 
 this appears to be long drawn out, and scattering indi- 
 vidual larvse and pupa? may be found throughout every 
 month of the year. The finding of eggs as late as Sep- 
 tember 18 has been reported from Michigan. As a rule, 
 however, the insects pass the winter in the adult stage 
 (fig. 1) within the roots where they developed. During 
 May they abandon the old roots and seek out fresh 
 plants or fields in which to lay their eggs. The eggs 
 are mostly deposited between the middle of May and 
 June 20. The female gouges out a shallow cavity, 
 more often in the crown of the plant, sometimes at 
 the sides of the root even 2 or 3 inches below the 
 crow n, and in this places, singly, hut not far separated, 
 about half a dozen pale whitish, elliptical, very minute 
 eggs. These hatch in about a week, and the larvae (fig. 2) for a time 
 [Cir. 119] 
 
 Fig. 3.— The clover 
 root - borer: 
 Pupa. Much en- 
 larged. (Au- 
 thor's illustra- 
 tion.) 
 
feed in the excavation made by the mother, hut soon burrow down- 
 ward into the root, and before the 1st of August the majority of 
 them have become fullj grown and passed into the pupal stage 
 (fig. 3). B3 October nearly all have become fully developed beetles, 
 hut they make qo attempt to leave the plant until the following 
 spring. Bach states thai the adults fly at 
 Omegnen in March and April, while EichhofF 
 has observed them near Mulhausen, swarming 
 during the warm afternoons aboul the middle 
 of June; bul these observations were all made 
 in differenl parts of Europe. In our own 
 country, in Ohio, the adults are abroad and 
 have been swepl from clover fields early in 
 May: bul no swarming of the beetles has been 
 observed, though it is clear that they may 
 migrate about that time of the vear. 
 
 ~r 
 
 FOOD PLANTS. 
 
 In Europe, besides red clover and alfalfa, 
 the species is known to attack Scotch broom, 
 Cytisus Spartium 1 scoparius, and goat root or 
 yellow-flowered rest harrow (Ononis natrix). 
 In America it has so far been especially de- 
 structive to red clover (Trifolium pratense), 
 yet with the recently increasing interest in 
 the growing of alfalfa (Medicago sativa) in 
 the Northern States it may be expected to 
 become destructive to that crop also. Besides, 
 it is known to attack mammoth clover (Tri- 
 folium medium) and alsike (T. Tiybridum). 
 The fact that it also injures the garden pea 
 will be very suggestive to growers of peas for 
 canneries, and indicates the undesirability of 
 sowing pea-- early in the season on ground 
 that has recently keen in these clovers or 
 lying adjacent to the infested clover fields. Late-sown peas, how- 
 ever, would probablj nol become sufficiently large to invite attack 
 until after the hectics had appeared and gone. 
 
 Fig. 4.— 1 iwlng 
 
 work of cl 
 Slight 
 
 METHOD < )F ATTACKING RED I LOV1 i: 
 
 The insect's method of attack is well illustrated by figure I, show- 
 ing a clover root spin in two, exposing the excavations. In • 
 of extreme abundance, however, almost the entire main root. 
 except the hark, is eaten, the substance being displaced by 
 
 [Clr, 1 L9] 
 
excreta, and the dead top either becomes detached of itself or is 
 easily broken off if one attempts to pull up the plant. It will be 
 observed at once that until the roots have attained sufficient 
 dimensions it will be impossible for the insect to attack them. Over 
 the territory where red clover is grown in this country the seed 
 is sown either during late winter or spring; and during the first year 
 the roots of the plants have not yet attained sufficient size to 
 accommodate the insects at the. time the latter are, with the excep- 
 tion, perhaps, of a few belated individuals, abroad and depositing 
 their eggs; and thus the plants are almost, if not, indeed, entirely, 
 exempt from attack the first year. Hence it is not until the sum- 
 mer of the second year that the plants are destroyed. This has led 
 European entomologists to believe that, like many others of the Scoly- 
 tida?, the insect does not attack the plant until the latter has become 
 weakened by age or is diseased. But in this country, at least, this 
 can not be true, for the reasons just given. It is not improbable, 
 however, that, as between two plants with roots of the requisite size, 
 an unhealthy one would be preferred by the beetles rather than one 
 in a thoroughly vigorous condition. But as yet there have been 
 no observations tending to verify this hypothesis. A diseased clover 
 root, or one that has begun to decline from effects of age, is first 
 affected at the heart ; and, as will be observed from figure 4, this is the 
 part first attacked by the root-borer. 
 
 EFFECT FPON THE PLANT. 
 
 While an infested clover plant sooner or later succumbs to an attack 
 by this insect, life may be lengthened or shortened by meteorological 
 conditions. Thus, if the spring or early summer is very dry, the 
 plants begin to die in patches late in June, as soon as the hay crop is 
 removed; but if there is much rain during this period, the weakened 
 plants may continue to live until winter, dying out before spring. In 
 either case the farmer is likely to be misled and to attribute the loss 
 to the weather. The summer of 1005 was not a dry one. Copious 
 rams fell with sufficient frequency to enable all but the most seriously 
 affected plants to survive. A prominent seedsman of Indiana, who 
 was much among clover fields, thus described the situation in October: 
 
 In driving around this year and examining clover fields, we have found that several 
 fields which apparently should have pn >dueed an immense amount of seed, or al least, 
 say, 3 or 4 bushels to the acre, * * did not shake out, anythinm. We pulled up 
 
 some plants and discovered that the planl broke off at the crown; or if any of the root 
 did come with it. it was small and decayed. ( 'n close investigation we discovered a 
 little white worm which seemed to be in abundance and working amongst the roots. 
 \\ e not iced this in a number of fields and have been wondering what it was. We have 
 ;d-o had samples of clover plants from other seel ions of I ndiana showing these condi- 
 tions, and almost invariably the yield of such fields was less than a bushel per acre, 
 and in many instances hiillinu was abandoned and the huller taken out of the field. 
 I fir. 1 19] 
 
N VI I a \I I.MMll s. 
 
 While Doctor Riley found the larva of one of the common soldier 
 beetles, probably Telephorus MLineatus Saj , attacking the Ian ae of the 
 borer, and although it probably has other enemies, both among 
 insects and birds, these have so far proven of little economic impor- 
 tance. 
 
 rui.\ ENTIVE MKAsi RES. 
 
 The only preventive measure yel tried thai gives any promise of 
 success is summer fallowing as soon as the hay crop is removed. 
 
 At this time the young arc in an immature state and. if deprived 
 of food, musl perish. They can not migrate from one clover root to 
 another, and, if the meadow is now broken up, throwing the roots 
 up tn the hoi sun and winds, these wither and dry, thus no longer 
 supplying the necessarj sustenance, at this time so imperative to the 
 life of the larvse, and they perish. Thus an invasion of a new field 
 from an old one maj be prevented. Bui if the fallowing be delayed. 
 even for a few weeks, t he larva 1 will then have for the most pari passed 
 into the pupal stage, during which no food is required, and plowing can 
 have little or no ell'ect upon them. This measure, together with the 
 practice of allowing clover fields to stand only two years, would soon 
 reduce the pesl to subjugation in anj community. No trouble from 
 its work seems to occur in pastures. Once brought under control, 
 it would seem thai a system of rotation that involves mowing for 
 
 hay and seed the Qrsl year, and pasturing and then breaking Up the 
 
 ground the following year, if generally followed in a community, 
 would suffice to keep the pest in subjection. Extermination is nol 
 possible. 
 
 Approved : 
 
 James Wilson, 
 
 Secretary <;/" Agriadturt . 
 Washington, I). ('.. January l '., 1910. 
 
 [Cir. 119] 
 
 o 
 
UNIVERSITY OF FLORIDA 
 
 3 1262 09216 5561