Mtu^^^^^^-^ti^ UBRARY STATE PLANT BOARD Circular No. 18, Second Series. (Revision of No. 14.) United States Department of Agriculture, DIVISION OF ENTOMOLOGY. THE MEXICAN COTTONBOLL WEEVIL. (Anthouomus grandis Boh.) SCOPE OF THE CIRCULAR. Circular No. 6 was published in April, 1895, and coutained a brief report of the observations made up to that time, and the conclusions based on those observations, concerning the Mexican cotton-boll weevil, an insect of Central American origin which, during 1894, attracted considera ble attention in th( cotton fields of south Texas. The investi- gation was continued during the summer, fall, and early winter of 1895, especially by My. Schwarz, who visited Texas in May and June and again from October to De- cember, and by Mr. Townsend, who was stationed in the State during the greater part of the summer. The writer went to Texas in December, and in company with Mr. Schwarz carefully studied the con- dition of affairs at that season and talked with many prominent cot- ton growers. The results of these supplementary investigations were published in Circular No. 14, which was issued both in English and in Spanish. During 189(> still other investigations were made by the gentlemen mentioned and by Mr. C. L. Marlatt, who studied especially the question of remedies, and the results obtained necessitate the pub- lication of still another circular on the subject. In this circular all of the essential points of the previous circulars have been repeated, the section on remedies has been entirely rewritten, and a paragraph has been added on the work of the weevil during 1896. GENERAL APPEARANCE AND METHOD OF WORK. This insect is a small, grayish weevil, of the shape and general appearance shown in fig. 1, a, and measuring a little less than a quar- ter of an inch in length. It is found in the cotton fields throughout Fig. 1.- -Aiithonomus grandis: a, adult ])e('tle: enlarged. '>, pnjia; c. larva — all SB the season, panctiiring and laying its eggs in the squares and bolls The larvcT, of the shape and appearance shown at fig. 1, c, and measur ing a little over three eighths of an inch in length when full grown live within the buds and bolls and feed upon their interior substance The squares attacked usually drop, but most of the damaged bolls remain upon the plant and become stunted or dwarfed, except late in the season, when they either dry or rot. DISTRIBUTION. This insect through its ravages caused the abandonment of cotton culture around Monclova, Mexico, about 1862. Two or three years ago Pig. 2.— Map showing distribution of the Mexican cotton-boFi woevil. cotton w^as again planted in that vicinity, but the weevil immediately reap])eared and destroyed the cro}). At Matamoras tlie weevil was noticed eiglit or ten years ago. About 1893 it crossed the river at Jirownsville, and in 1804 was noticed in the country around 8an Diego, Ahce, and IJeeville. At the (^lose of tiie season of 18!)1 the insect occu- ])ied a territory extending to tlie north a little beyond Beeville, a few miles to the east of that i)oint, and southwest to the neigiiborliood of IJealitos, on the National INIcxican Jvailway. Tlie greatest damage seems to have been done along the lower Nueces liiver. During 1805, and particularly in tlie latter part of tlio season, it extended its ran^e to a considerable extent. Toward the east it was found in moderate abundance alon<;- tlie valley of tlie (luadaloui)e Kiver at Victoria, Thoniaston, and Cuero. North of its old ran<;e it extended to Kenedy, Floresville, and many points in the country lyin^- between tin* hitter ])lace and Cuero. A single held was found near San Antonio which contained weevils in large numbers, and in tlie same way a single Held was found far to the east at Wharton in which the weevils had appeared late in the season. The exact localities where the insect was found during' 1895 are indicated on the accomi)anying map. AVORK OF THE WEEVIL IN 18V)(J. It was feared that during 1896 there would be a further spread of the weevil, but for some reason, probably on account of the severe midsum- mer drought, there was not only no spread beyond the lindts indicated on the 1895 map, but, on the contrary, a shrinkage of the territory infested. The main spread in 1895 took place in the autumn and at the outer boundaries, as at San Antonio and at Wharton the weevil was unquestionably killed by the winter frosts. In a field, for example, near San Antonio, which was several times examined in 1895 by Mr. Schwarz, ]\Ir. Townsend, and by the Avriter, and in which the weevil was extremely abundant down to the month of December, not a trace of the insect could be found in 189G. In 181)6 the drought prevented the '•make" of the toj) crop at many points, and there was little food for the autumnal generations of the weevil, and therefore a lesser sx)read from the localities of successful hibernation. NATURAL HISTORY AND HABITS. The insect passes the winter in the weevil state. It can be found on the cotton plant until late in I)ortion of the plant is green. It is found most abundantly in the earlywinterhidden between the involucre and the boll, and later it frequently works its way down into the dry and open bolls. All the specimens found by Mr. Schwarz in such situations in the late spring of 1895 were dead; but Mr. Townsend found a few living in March. The dry boll is probably not a fre- quently successful hibernating place. Judge S. G. Borden, of Sharpsburg, however, writing under date of January 27, 1896, states that the weevil at that time was being found nearly every day in the dry bolls; but this statement lacks the sig- nificance which it might other- wise have had as bearing on December, and, in fact, as long as any Fig. 3 newly hatched larva in young square; b. nearly full-grown larva in sitii; c, pupa in young boll picked from ground. the question of hibernation from the fact that no heavy frost had proba- bly occurred up to that time at Shari)sburg. Witli tlie cutting of tlie plants or witli the rotting or drying of the bolls as a result of frost, the adult weevils leave the plant and seek shelter under rubbish at the surface of the ground, or among weeds and trash at the margin of the fields. Here they remain until the warm days of spring, Avhen they fly to the first buds on such volunteer plants as may come up in the neighborhood. They feed on these and lay their eggs on the early squares, and one, or perhaps two, generations are developed in such situations, the number depending upon the character of the season and the date of cotton i^lanting. By the time the planted cotton has grown high enough to produce squares the weevils have become more numerous, and those which have developed from the gen- eration on volunteer cotton attack the planted cotton, and through their punctures, either for feeding or egg-laying, cause a wholesale shedding of the young squares. It seems to be an almost invariable rule that a square in which a weevil has laid an egg drops to the ground as a result of the work of the larva; in the square on the ground the larva reaches full growth, transforms to pupa, and issues eventually as a beetle, the time occupied in this round approximating four weeks. Later, as the bolls form, the weevils attack them also, and lay their eggs in them, and the larva3 develop in the interior just as with the squares. The bolls, however, do not drop. Fig. 3, a and h, show the larv?e in the squares, and c, a young boll cut open and the pupa in its customary position. There is a constant succession of generations from earl}^ spring until frost, the weevils becoming constantly more numerous and the larvai Tig. 4. — Mature Ijoll cut open at left, showing full-grown larva : the one at the right not cut, and showing feeding punctures and oviposition marks. and pup«ne as well. A single female will occupy herself with egg-laying for a considerable number of days, so that there arises by July an inex- tricable confusion of generations, and the insect may be found in the field in all stages at the same time. The bolls, as we have just stated, do not drop as do the squares, but gradually become discolored, usually on one side only, and by the time the larva becomes full grown generally jcrack open at the tip. While in a square one usually finds but a single larva, in a full-grown boll as many as twelve have been found. In any case, however, the hatching of a single larva in a boll results in the destruction of the boll to such an extent that its fiber is useless. Where no serious frost occurs in December, the insects all, or nearly all, reach maturity and enter hibernating quarters, although larva' have been found on into January at 8harpsburg. Whenever a heavy frost comes ill this montli, or before, the ()l)seivations of last fiijl show that tliose insects wliich liave not rea(;he(l tlie beeth*. sta«»e are nearly all killed. From this fact it follows that the insect will i)robably not jirove as injurions in other ])ortions of the cotton belt as it is iu southern Texas. It was found durin <»■ the latter part of 1895 that the weevil w^as i)resent in anumber of localities in which it was not known by the planters themselves to occur. It is impor- tant that every planter who lives in or near the region which we have mapped out should be able to discover the weevil as soon as it makes its appearance in his fields. Where a field is at all badly infested the absence of bloom is an indica- tion of the presence of the insect. In the early part of the season the weevils attack the squares first, and these wilt and droj) off. A field maybe in full blossom, and as soon as the insect spreads well through it hardly a blossom will be seen. This dropping alone, however, is not a sufficient indication of the weeviFs presence. KSquares are ^, . j , . u ^ ^^ i, , -, ^. .n on • ^^ 1 ■ Fk;. ;).— Late fall boll, show- shed irom other causes, but it a suiDcient number mg bow beetles iiide be- ef fallen scjuares are cut open the cause will be tween boii and involucre. apparent. The characteristic larva of the weevil will be quite readily recognizable on comj)arison with the figures which we publish herewith. As stated above, the bolls do not drop. The punctures made by the weevils in feeding, however, are comparatively characteristic, and where a boll is discolored and has begun to crack at the tip the larva or the pupa can be seen without trouble on cutting it open. Late in the season the weevils themselves will be found between the involucre and the boll, as shown in fig. 5, or in their absence the feeding marks and the yellow, granular excrement which collects in the involucre at the base of the boll are excellent indications. POPULAR NAMES. In south Texas, among Spanish -speaking people, the insect is gener- ally known as the "picudo," a descriptive name which refers to the snout or beak of the insect. English-speaking planters generally referred to the insect at first as "the sharpshooter," a term which for many years has been applied to any insect which causes through its punctures the shedding of the sc^uares or the rotting of the bolls. As there are sev- eral native insects that are commonly called sharpshooters, and which, though injurious, are by no means to be compared with this insect, it becomes necessary to discourage in every way the use of the word sharpshooter as applied to this weevil. This was attempted in the first edition of the circular by illustrating one of the commonest of the insects ordinarily termed shari)shooters, calling attention to the radical differences which exist between it and the weevil under consideration. The adoption of the term "Mexican cotton-boll weevil'' for the new pest is recommended. The term sharpshooter is now much less gener- ally apx^Med to the weevil than it was at first. Planters generally' now refer to it as the boll weevil, or the Mexican weevil, or the Mexican boll weevil. PARASITES AND NATURAL ENEMIES. It is safe to say that little assistance will be derived from the work of natural enemies and parasites upou this insect. Of the former none of any importance have been found. Several j^arasites, however, have been found to attack it, and in one or two locah'ties some little good has resulted from their work. The}^ have only been abundant, how- ever, late in the season, after the weevil has completed its damaj^e for the year and at a time when a minimum of good can be accomplished by the destruction of the larva. The majority of the weevils in a given field fail to hibernate successfully, being killed by cold weather or some other cause, so that the work of parasites at this time does not count. Careful estimates, however, show that from 15 to 20 per cent of the weevil larvie in fallen squares in Xovember, 1895, at Beeville and Kenedy were destroyed by parasites. REMEDIES. In considering the matter of remedies it should be understood at the outset that experience has shown that none of the general applications of insecticides are of the slightest value against this species as a means of protecting infested fields. The weevil in its work in growing cotton is thoroughly protected against poisons, breeding as it does within the blossoms and squares. As demonstrated by the exi)erience of the spring of 189(5, poisons may, however, be used as a means of destroy- ing overwintered beetles on volunteer cotton. The beetles which have survived the winter collect in the early spring on the first sprouts which appear on old cotton and eat the partially expanded leaves and the tender leaf stems, and at this stage can be poisoned by the appli- cation of an arsenical to this new growth. To do tliis it will be neces- sary to thoroughly spray the growing tips, and this should be done when volunteer cotton is very small, preferably mere sprouts or bunches of leaves an inch or two in length; later on the growing parts can not be easily reached. With an ordinary knapsack pump a field may be gone over rapidly and the volunteer cotton thoroughly treated, the nozzle being directed at each growing tip. The first application should be made as soon as the volunteer plants sprout, and ])erhaps repeated two or three times within as many weeks. As o dinarily cultivated, the number of volunteers is small and the time required for the thorough spraying of such plants will not be great. A strong solution should be ai)plied, viz, 1 pound of the poison to 50 gallons of water, because no harm will be done if the volunteer plants are ultimately killed by the I)oison. The practicability of this method has been demonstrated, but it has been abundantly shown that the very best system of control of the weevil is in a system of cultivation of cotton, to be later described, which will ])revent all i)ossibility of volunteer growth whatever. The poisoning and the other x^alliative measures relative to Aolunteer growths are given, therefore, merely as a means of correcting an evil which may result if the cultural system referred to has been neglected. These remarks api>ly, for instance, to the trap system, Avhich we have hitherto recommended among others. This consists of attracting the earliest beetles to a few cotton plants left at convenient points and i)rotected from winter killing by forced watering, so that they will branch out and ac(iuire buds often in advance of volunteer cotton. From these the beetles may be collected by hand when they are attracted to them by the first warm days, or, preferably, these plants may be poisoned, as already suggested. The fact that the spring generation develops only u|)()n volunteer cotton has suggested the possibility that the insect will not spread beyond the region Avhere volunteer cotton will grow in s])ring, but unlbrtiinately this possibility is by no means absolutely to be niiied upon. Neveitheless, the destruction of su(*h voliiiitcu'r i)lants as come up in corntields and in abandoned lields which the ])re\ ions year were l)lanted to cotton, unless they be systematically poisoned, can not be too strongly recommended, for it is a matter of observation that the shade afforded by the corn or the rank-growing weeds which come uj) iu abandoned lields is especially favorable to the development of the weevils. While the plauts are young, and where labor is as chea]) as it is in south Texas, a great deal of good can be accomjdished by i)icking and burning the fallen squares, and if this is done promptly a large num- ber of the insects will be destroyed. It should be done at least twice, at iutervals of three weeks, during the period while the plants are small. As soon as the jdants begiu to branch out, however, this method becomes impracticable, on account of the difidculty of tinding the squares on the ground. The idea of iHcking the affected bolls during the cotton i)i eking was suggested in the writer s first published account of this insect. It was thought that the aftected bolls could be so readily recognized that many thousands of the insects could be destroyed by the cotton pickers by picking these affected bolls and carrying them away in a separate receptacle to be burned. The amount of extra labor involved in this operation, however, would be very considerable, and the affected bolls in many instances are not to be recognized at a glance. During the past year Mr. Stronhall, of IJeeville, has devised a machine for jarring the affected squares and blossoms from young cot- ton jdants and collecting them at the same time. This apparatus has been given a partial demonstration the past season, but was not seen at work by any of the entomologists engaged in the investigation. It is arranged to brush the cotton from both directions vigorously, and the loosened bolls and squares are caught on receiving traj^s and ulti- mately burned or otherwise destroyed. The brushes work in o])posite directions and strike the cotton i)lants on either side. It can be adjusted to plants of different ages. The careful investigation of this weevil during the past two or three years by the Division of Entomology has fully demonstrated the supreme importance of the cultural method of control, to which fact we gave si^ecial prominence in our first circular on this insect. There can be no question now that in the proper system of growing cotton a practically complete remedy for the weevil exists. In the first place, it has been established beyond question that the conditions of cultivation which make volunteer growth possible also make the continuance of the weevil inevitable. Of first importance is the early removal of the old cotton in the fall, preferably in November or earlier. This can be done by throwing out the old plants with a plow, root and all, and afterwards raking them together and burning them. This treatment should be followed, as promptly as may be, by deep ])lowing, say to a depth of 6 or 8 inches. This leaves the field comparatively clean of old cotton stalks, facilitates thorough cultivation the following year, and, at the same time, collects and destroys all of the weevil larvie and pupie in the cotton at the time, and also most of the adults. The escapijig beetles will be buried by deep plowing, and will not again reach the surface. Few, if any, of them Avill succeed in hibernating in the absence of the ordinary rubbish in the fields in which they winter. Fields treated in this way have given a practical demonstration of the usefulness of the method. 8 UNIVERSITY OF FLORIDA Illillllll 3 1262 09228 3299 The greatest danger from the weevil is due to the presence of volun- teer cotton, which means early food for the weevils in the spring and abundant means for their overwintering, and tbe effort made to retain volunteer and get early cotton, or the "first bale," is a very serious menace to cotton culture within the weevil district. This cultural method, if generally practiced, will undoubtedly prove a perfect remedy for upland cotton, and will vastly reduce weevil damage in the lowlands, where the weevil is more apt to winter, perhaps in adjoining woods or roadside vegetation. The e^j removal of cotton by the means suggested is especially advised wlienever tbe presence of the weevil shows that the picking of a top crop is problematical. In such instances it would be well to uproot and destroy cotton stalks in September or October, as would have been thoroughly feasible for much of the ui)land cotton in 1896. If this cultural method can be enforced, either by State legislation or by the cooperation and insistence on the part of landowners that their renters shall carry out the system out- lined, the weevil difficulty can undoubtedly in very large measure be overcome. In connection with the system of fall treatment of the cotton, con- stant and thorough cultivation of the growing crop as late as possible is of considerable value, and is also what should be done to insure a good yield. With a crossbar to brush the plants many of the blos- soms and squares containing weevils will be jarred to the ground and buried, together with those already on the ground, in moist soil, and a large percentage of the material will rot before the contained insects have developed. It will be greatly to the interest of all growers of cotton in the prolific district lying to the northeast of the region at present infested to urge the passage of an act during the session of 189G-97 which will bring about the enforcement of remedial work in 1897. This act should pro- vide for the appointment of commissioners in each county upon the application of a certain number of the citizens of that county. These commissioners should be empowered to enforce remedial work, to levy penalties, or to have the work done by their own agents, the cost to be assessed upon the proi^erty. It will be well to let this law have a wide bearing and not to confine its application to this i)articular insect, but cover all injurious insects, in case of future emergencies of a similar nature. Such a law should be passed in every State in the Union. Though it might remain inoperative for years, its application would be available in case of any sudden emergency, snch as the introduction from a foreign country of a new injurious insect, or the sudden multi- plication and spread of any one of our native species. L. O. Howard, Entomoloylsi, Approved : Ohas. W. Uabney, Jr., Assistant Secretary, Washington, D. C, February 4, 1897.