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BULLETIN NO. 176 ,z.... JANUARY, 1931
UNIVERSITY OF WYOMING AGRICUL TURAL EXPERIMENT STATION
Bulletins will be sent free upon request. Address: Director of Experiment Station, Laramie, Wyoming. UNIVERSITY OF WYOMING Agricultural Experiment Station LARAMIE, WYOMING BOARD OF TRUSTEES Officer. WILL M. LyNN · President JOJ;EPH A. ELLIOTT Vice President FHI':O W. (;EDDES Treasurer FA Y E. J;AllTH , Secretary Ie. D. Ji'ULLER Ftscal Agent Executive Committee WILL M. LYNN ~'RANK A. HOLLlDAY JOSEPH A. ELLIOTT WALLACE C. BOKI> Appoin ted Members Term Expires 1921 ; JOSEPH A. ELLIOTT 1933 1921. FRED W. WWOES 1933 1923 FRANK ALAN HOLLIDAY 1933 1925 HARRIETT T. GRIEVE 1931 1925 J. M. SCHWOOB 1931 1927 WILL M. LYNN 1933 192Q WALLACE C. BOND 1935 1929 MABELLE G. OVlATT 1935 FHAXl\. C. E~J1~H~U~, Governor of \V)·omillg ...... •.•..••...... Ex Ofticio I\ATIIA HI"E A. MOHTO", State Superintendent of Public Instruction Ex Ontclo A. G. CHANE, Ph.D., President of the Uutveraity ...... • , ...... ••..... Ex Offtciu STATION STAFF A. G. CIlA"E, I'h.D Preaideut J. A. HILL, B.S Wool Specialist. IJirettor FAY E. SMITH . Secret,"·y M. A. ALEXANDEH, M.S Assistant Animal Husbandman o. A. DEATH, M.A...... •...... Sta tiun Chemtst "ROBERT II. BURNS, M.S...... Assistant Wool Specinl ist. C. L. COR.KINS, M.S Research Assoctate Entomologist and Apiculturist T. J. UU~~E'VALIJ. Ai.S...... Asst-a.uu soil lnvest iun tious *tJ. E. ECKERT, M.S Associate Apiculturist U. S. Bee Culture Field Station CECIL ELl>b:H, D.V.M., !l.S : Resen rch [,,,tholo;:ist *II. F. EPPSON, B.S...... Asslstnnt Chemist C. itA HIlLI) (;ILIJERT, AJ.J; Asaistu ut Research Apiculturist C. 8. (;IL13F:HT. M.A ...... •.•.••.•...... Aselstum Research Chemist GLEN HARTMAN, M.S Assistant Agronomist FIlA:\I( E. ItI'PNER. M.S Head of Weather' Station HALPH HONESS, B.A Assistant Research Zoologist FIII,IJ S. III'LTZ. Ph.D Animal Husbandman R. S. JUSTICE. B.S Assistant Cbemist FHANK J. KOHN, B.S Assistant Animal Husbandman AUBHEY M. LEE, D.V.M., ~l.S Assistant Vcterinarian D. C. lle('HEA [lY. I'h.I> Assistant Chemist EUZA BI'TII .l. Mcl\lTTRICI(, 1l.S Home Economics AVEN ~mLS()"'. Ph.D...... Botanist and Horticulturist IIA IlHY I'I-:AIlR():\. B.S Assistant Agronomist W. L. QI'>\YLI<:. H.S ...... ••.••...... Director of Exper imeut 1'-"~II'ms W. A. HIEDL, B.S Assistant Agronomist Il)}-J\ \r !'IITT. I'h D...... •••...... •...... ZoologiRt »n.l Psrnsi tologiat L. H. SCRIVNER, D.V.M Assistant Veterinarian tAo P. STUHTEVANT, Ph.D ...... Associate Apiculturist, in charg-e of U. S. Bee Cult lITE:' Fjeld Station EMMA J. THIESSEN, M.A ...... •...... •..... Assistant Home Economies A F' V \...... I'll I...... •...... •...•.. Ag-ronomist S S \\'11' "'YR . .\1 S...... •• ..•...... Asststnnt Anim.d Hushuudnutu JAMES R. WTANT. Ph.D Assistant Agronomist, Plant Pathologist H. S. WILLARD, M.S Assistant Animal Husbanrlrnnn MAHY MARKS. B.L.S Librarian JANE M. NEAL Clerk
·On leave of absence. tIll {'00J)f>rRtion with the U. H. Department of Agriculturp.. THE MEXICAN BEAN BEETLE
By HARVEY L. SWEE'I'MAN* The Mexican bean beetle is one of the few destructive spieces of the otherwise highly beneficial lady-bird family. Some of the members of this family are among our most valuable predatory in- sects, feeding upon plant lice, scale insects, soft-bodied larvae, and the eggs of insects. The species, Epilachna corrwpta Muls., is the most destructive bean pest in the United States. When first found in Wyoming in 1924 it was causing considerable damage to cultivated beans. The insect is a potential pe t that can become very destructive to beans in the state if the climate is suited to it. The primary purpose of this study is to determine the probabilities of the bean beetle becoming a serious pest in Wyoming.
DESCRIPTION OF STAGES AND INJURY All stages-eggs, larvae, pupae, and adults-of the bean beetle are conspicuous in the field. The eggs are pale or orange-yellow in color, nearly elliptical in outline and about twice as long as wide. They are attached to the leaf by one end laid irregularly in groups of about fifty on the under side of the leaves. (Fig. 1.) The larvae have four stages, molting three times previous to the pupation molt. The newly hatched larvae are about one-six- teenth of an inch long, pale greenish-yellow in color and have their bodies armed with spines. The developing and mature larvae are yellow, with six rows of spines which become strongly branched and black at the tip . (Fig. 1.) When over half grown they ap- pear to be "humped", the longest spines and the thickest portion of the body being in the middle. The abdomen in all stages tapers to the hind segment, which is produced to form a sucker-like apparatus by which the larvae are aided in clinging to the leaf, and by which they fasten themselves previous to molting. They are about one-third of an inch long when mature. (Fig. I.)
'Acknowledgments are elue Mr. Ceorae Boyd, County Agent of Platte County.. who rendered valuable assistance in the preparation of this paper. 4 Wy01ning Aqricultural Es periment Station But. 176
Figure 1. The various stages of the Mexican bean beetle on " bean leaf. Courtesy 01 the U. S. Bureau of Entomology.
The pupae are light yellow in color, spineless, and about the size of the adults. They hang head downward from the under surface of the leaves and are partly covered and protected by the shed larval skins, which are attached by the po terior end to the surface on which they are fastened. (Fig. 1.) The robust, semi-ovoid adults are about one-fourth of an inch in length and one-fifth of an inch wide. When newly emerged the color is lemon-yellow, but gradually darkens with age to brown or bronze. Usually each wing cover is marked with eight small black spots. (Fig. 1.) Both the adult and larval tages are destructive. The beetles cut irregular holes through the leaves, leaving portions of the tis ue and the larger veins. (Fig. 1.) The larvae are voracious feeders, and do more harm than the adults. At first they feed in colonies near the old egg mass on the lower surface of the leaf, but soon become scattered as they crawl to other leaves in earch of food. Jan. I93I The Mexican Bean Beetle 5
Figure 2. Typical injury to bean plants produced by the Mexican bean beetle. Courtesy of the U. S. Bureau of Entomology.
They consume the lower layers of the leaf, leaving the upper epi- dermis and the larger veins. The upper ti sue soon die and bleaches out, leaving a white skeletonized appearance. (Fig. 2.)
SEASONAL HISTORY The adults of the Mexican bean beetle emerge from hiberna- tion in the spring after the advent of warm weather and locate uitable food plants, principally beans. Egg-laying begins in about a week or ten days after the beetles appear, the egg generally being attached to the under surfaces of the leaves. The over-win- tering adults may continue oviposition until August. Incubation of the eggs requires about one to two weeks. The larvae feed upon the leaves and pods for about three to five weeks, then attach themselves to the leaves and pupate; the adults emerging eight to twelve days later. The number of generation in a season is de- pendent upon the climatic conditions and length of season, and 6 WY01ning Aqricultural Experiment Station But. 176
will vary at different altitudes. Probably one to two broods will occur under most Wyoming conditions. The beetles enter hiber- nation in the fall in moist, protected places, remaining dormant or semi-dormant, depending upon the weather, until spring.
FOOD PLANTS The bean beetle is primarily an edible-bean pest, preferring the common bean, such as snap beans (green or string beans), kidney beans, pinto beans, navy beans, and lima beans to other kinds. Its second choice of food is the beggarweed. Meibomia. The insect can reproduce successfully on cowpeas and soybeans, but injury to these crops is unusual. The only important food plants in Wyoming are the cultivated beans, which would confine the bean beetle to the agricultural sections of the state.
DISTRIBUTION The beetle is a native of the southwestern part of the United States and Mexico. In the West it is now found in Wyoming, Colorado, Utah, Arizona, New Mexico, and Texas. It was discov- ered in Alabama in 1920 and has increased its range rapidly to the north and east since then. It spread to Georgia, Tennessee, North and South Carolina, and Kentucky in 1921; Virginia in 1922; West Virginia and Ohio in 1923; Pennsylvania, Indiana, and Mississippi in 1924; Maryland in 1926; New York, Michigan, and Ontario in 1927; Delaware and New Jersey in 1928; and Connecticut and Iassachusetts in 1929. Fortunately the spread in the West is much slower than in the East. The bean beetle has been a serious pest of bean in the West since the first reliable entomological record were taken. The pio- neer settlers in Colorado, Arizona, and New Mexico reported serious injury to garden beans from a very early date. Apparently the insect had dispersed as far north, at least, as Arizona and New Mexico when settlement of this territory began. Dr. C. P. Gill- ette, State Entomologist of Colorado, reported the bean beetle as being the most serious pest of beans in Colorado in 18g0, when it was well established at Fort Collins, only a few miles from the Wyoming state line. Jan. I9JI The Mexictui Bean Beetle 7
Fortunately the pe t did not invade Wyoming until recently. It was found and reported as a pest at Wheatland in 1924 by C. L. Corkins of the Wyoming Agriculture Experiment Station, but was well established at that time so had gained entrance to the state sometime preceding, 1924. The probabilities are very great that the jump was made from Colorado. Undoubtedly it was car- ried by some vehicle of man since the arid plain between the Colo- rado and Wyoming infestations was insurmountable to the insect at that time if left to its natural means of dispersal. Since the discovery of the insect's presence in 1924 it has demonstrated great potentialities of being a serious bean pest in the state, especially in the irrigated sections. PROBABILlTIES OF SPREAD AND INJURY IN WYOMING It is extremely important for the bean growers of Wyoming to know if the bean beetle will spread throughout the bean grow- ing areas and become a serious pest. Studies of the past distri- bution of the pest indicate that it is usually destructive wherever it becomes established. The one notable exception to this occurs at Thomasville, Georgia, and along the southern limits of its dis- tribution in the East, where it is held in check by a combination of high temperature and high humidity. (Sweetman, unpublished.) The widespread damage in the East and the West suggest the probability that it will be injurious in this state wherever it is able to maintain itself. It fact, the record of the bean beetle at Wheat- land has demonstrated its ability to injure the bean crop in Wyo- ml11g. It has been shown from field studies that temperature and moisture conditions are extremely important factors influencing the dispersal and abundance of the beetle (Sweetman, 1929). Since it was impossible from field data to determine which factor was the most important, laboratory experiments were planned so that the weather environment could be controlled and varied at will. The conclusions in this bulletin regarding the possible spread and destruction of the pest are based upon the results of that study.
DESCRIPTIO=" OF "\PPARATUS AND METHODS A well insulated 'cabinet containing six separate compart- ments was used. Each section had a capacity of twelve cubic feet. 8 Wyoming Agricultural Expe-riment Station But. 176
The top of the cabinet was made of glass so that the light intensity could be controlled from outside the cabinet. The doors, which were about two feet square, contained glass so that the insects and instruments could be observed without opening the compartments, except at feeding time or when the cages were being transferred from one environment to another to obtain the alternated condi- tions. The temperature was maintained with electrical heating units operated with thermostats and cold running water, the two working against each other. Relative humidity was controlled by placing saturated salt solutions in wide pans, so as to have a large amount of surface exposed, and measured with recording hygrom- eters. In order to obtain uniform conditions, fans were used to keep the air in motion. The fans were placed so that the air currents passed directly over the salt olutions. The experimental material was placed on wire shelves at about the middle of the compartments so that the air currents passed directly through them, thus exposing the contents to the surrounding environment. Temperature of any degree desired could be obtained, but relative humidity much below 32 per cent could not be secured. Generally, a salt could be found that would give the approximate humidity sought above 32 per cent to nearly saturation of the atmosphere. Since the normal laboratory environment was dry, the problem of control consisted of raising the humidity to the desired amount. All temperatures were recorded in degrees Fahr- enheit, and moisture data in percentages of relative humidity. Series of temperatures ranging fr0111 63 degree to 99 degrees at interval of 9 degrees were used. Moisture conditions varying from 32 to 93 per cent were maintained in the various temperature environments. Alternated conditions were obtained by transfer- ring the insect from one environment to another at definite in- tervals. Since inse t are cold-blooded animals, their metabolic rates are dependent upon the surrounding conditions. Thus, the effects of climate on such organisms can be determined by exposing them to artificial weather and recording their reactions. Temperature is an extremely important factor in the life of the bean beetle. It is closely allied with moisture and does not affect the pest as a Jan. I93I The Mexican Bean Beetle 9 single factor except when approaching the high and low tempera- ture limits. Moisture is as important to all stages of the insect as temperature, and probably affects it principally through changes in the evaporation rate. The evaporation rate is, in turn, influ- enced by the temperature and air movement. The velocity of the air currents is very important as the temperature and relative humidity about the plants approaches a state of equilibrium with the environment away from the plants in proportion to the move- ment of the air. No direct effects of light on the bean beetle have been observed, but the influences of light are secured indirectly through the food. It is extremely important to keep the insects supplied with fresh food. The larvae, especially, show signs of restlessness shortly after the plants begin to wilt. Since it is impossible to discuss the effects of temperature on the Mexican bean beetle without taking into consideration the influence of mois- ture, their reactions to both factors are considered jointly.
EXPERIMENTAL RESUL'l'S A summary of the effects of temperature and moisture is pre- sented below. The complete data from which this summary was made were published elsewhere (Sweetman, 1930), to which the reader is referred for details of the experiments. Effects on Adults. The adults were killed in a few hours when placed in a high temperature of 99 degrees regardless of the relative humidity of the environment. A temperature of 90 degrees with high humidity was very destructive to the acLults, but, with a low humidity of 32 per cent, was favorable to length of life and egg production. When alter- nated with lower temperatures (81 degrees, 72 degrees, 63 de- grees), the' adverse effects were largely overcome below 81 degrees and partially offset at that temperature. A temperature of 81 degrees was favorable to length of life of the adults with all humidities (32-93 per cent) used, and to egg production with humidities of 60 per cent and higher. High moisture environments were more favorable than low humidity conditions, but the difference was not so great as with higher tem- peratures. When alternating temperatures were used in moist en- 10 Wyoming Aqricult ural Experiment Station Bul, I76 vironments with 8r degrees, good egg production resulted with a temperature of 72 degrees. Humidities of 93 per cent or above may be detrimental to egg production. A temperature of 72 degrees with humidities of 40 to 90 per cent was favorable to length of life of the adults and to egg pro- duction, although the number of eggs laid was reduced in the dry conditions. High egg yields with alternating temperatures re- sulted in the 8r -degr ee and 9o-degree chambers with moist con- ditions, but production was low in the 63-degree, dry environment. A temperature of 63. degrees was favorable to length of life of the adults, but was near the minimum effective temperature for egg production. With alternating temperatures above 63 degrees, the rate of oviposition was in proportion to the number of hours at the higher temperatures, the greatest yield occurring in the combination with 90 degree in low humidity. Thus the adult beetle is capable of reproduction with tem- peratures ranging from 63 degrees to 90 degrees and with a rather wide series of humidities.
Effects on Eggs. The embryos were destroyed at a tempera- ture of 99 degrees in both wet and dry environments. A temperature of 90 degrees gave similar results in constant conditions, but with alternated temperature a few larvae hatched in the moist environment at 72 degrees. A temperature of 8r degrees produced a fair number of larvae in moist surroundings (60-93 per cent) but none in the dry, 32 per cent, conditions. Good hatches were obtained in the alternated conditions with 72 degrees, but not with 90 degrees. A temperature of 72 degrees produced good hatches in moist environments (60-90 per cent) and with alternated temperatures below 90 degrees. A temperature of 63 degrees was favorable to good hatching of the eggs with humidity above 45 per cent and with temperature cornbinatjons below 90 degrees, but the length of the mcubation period was increased considerably. This shows that the egg stage is a very critical one in the life cycle of the bean beetle. The eggs hatched well in the temperature Jan. I93I The Mexican Bean Beetle II conditions ranging f rom 63 degrees to about 86 degrees, but high moisture conditions were essent.al, This high moisture require- ment for incubation of the eggs is very important under Wyoming climatic condition . Effects on Larvae and Pupae. A high temperature of 99 degrees was just as destructive to the larval and pupal stages as to the egg and adult stages. About half of the larvae completed development at a tempera- ture of 90 degrees when the humidity was 32 per cent, while all of them succumbed in the 92 per cent moisture environment. The adults from larvae reared in the dried conditions were badly dis- torted. All of the larvae died in alternated humiditie (32, 92 per cent) at this temperature. The death rates were much re- duced when the temperature was alternated, but most of the re- sulting adults were monstrosities. A temperature of 81 degrees wa favorable for larval develop- ment with high humidity, while the death rate was very high in dry environments. Alternated surroundings with 90 degrees were un favorable with long exposures to the higher temperature, but were very favorable in the 72 degree alternations. A temperature of 72 degrees was very favorable for larval development in all moisture conditions used (40-9° per cent). The number pupating was much reduced at 90 degrees in the alternating temperature experiments. A temperature of 63 degrees was favorable for completion of larval development, but growth was very slow. High percentage of the larvae matured in alternating conditions, but the time neces- sary for maturation was greatly increased. Thus it is easily seen that the reactions of the larvae and pupae to moisture and temperature are much nearer to those of the adults than to the unhatched embryos. It is evident from the above data that development during the egg stage is the most sensitive period during the summer activities of the bean beetle. This serisitive period is carried over into the first few days of larval life also. This fact is extremely important when considering the possible prevalence, destruction, 12 Wyoming Agricultural Experiment Station Bul. I76 and dispersal of the pest. Abundance and inj ury are definitely limited to areas having suitable ranges of temperature and mois- ture. Distribution, however, is not so closely limited as dispersal occurs in the adult stage. Since the beetles are strong fliers, capa- ble of flying several miles during a single or a few flights, very rapid dispersal is possible. On years when moisture conditions are favorable this permits rapid spread and increase in areas where the pest is unable to maintain itself normally. Since the insect hibernates in the adult stage, the reactions of the beetle during dormancy to temperature and moisture become important. Apparently the beetle is capable of withstanding rather low winter temperatures, since it commonly hibernates in the foothills of Colorado (Daniels, unpublished), indicating that low temperature alone cannot be relied upon to destroy the pest in the bean growing areas of Wyoming. However, the moisture re- quirements of the adults during hibernation are rather high. This shows again that moisture is the most important factor in limiting the distribution in the West and Southwest (Sweetman, 1929).
Figure 3. The average annual precipitation for Wyoming in inches. (After Hepner). Jan. I93I The Mexican Bean Beetle
CLIMATE IN WYOMING Since the destruction of the bean beetle in the West is de- pendent upon moisture rather than temperature, special attention will be given to that factor in the study of the Wyoming environ- ment. A glance at the precipitation map (Fig. 3) clearly shows tha1 the annual rainfall of a greater portion of the state is below 20 inches, and much of the area below IS inches. If the warm season only (April to September inclusive) is considered, prac- tically all of the agricultural sections have less than ten inches of rainfall (Fig. 4). Further, the aridity of the atmosphere can be shown by study- ing the relative humidity maps for the region. Ordinarily, the highest relative humidity occurs in the early morning hours and the lowest relative humidity in the early afternoon hours. Thus the moisture extremes can be approximated by using the 8 a. 111. records for the maximum and the 2 p. m. records for the minimum. For the purpose of this study the data for the months of January and July can be used to represent average summer and winter con-
Figure 4. The average warm season (April to September) precipitation for Wyoming in inches. (After Atlas of American Agriculture). W y011ling Aqricult ural Espcriutent Station B ul. I76 ;:;~.~:[O'~ ,.... 1"'" I I \ I I UMioUj------',
Figure 5. The average relative humidity in January at 8 a. rn, for Wyoming. (After Atlas of American Agriculture).
I 1 j"'''' _.,,=- ...·-- ..1 I '1 I I .1
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Figure 6. The average relative humidity in July at • a. m. for Wyoming. (After Atlas of American Agriculture). Jan. I93I Th e ~Mexican. Bean Beetle IS
ditions. The maximum condition are shown in Figures 5 and 6 and the minimum conditions in Figures 7 and 8. The umrner humidities of 25 to 30 per cent for the minimum and 65 to 70 per cent for the maximum show an extremely dry atmosphere during a portion of the clay that is very inj urious, a has been shown above, to the eggs and young larvae of the bean beetle. The winter moisture conditions of S0 to 75 per cent likewise expose the hiber- nating adults to a considerable amount of dehydrating atmosphere during a portion of the day, so that they are unable to over-winter unless moist, protected places are available. Such places are lack- ing over the greater part of the plains region of Wyoming. These dry conditions explain why the insect has not become a pe t throughout the dry farming communities about the Wheatland dis- trict, yet it remains a potential pest to the bean growing industry of the state that is capable of destroying the crop and successfully extending its range when favorable climatic conditions present themselves. Perhap the greatest danger involved is the chance
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Figure 7. The average relative humidity in January at 2 p, m. for Wyoming. (After Alias of American Agriculture). 16 Wyoming Agricultural Experiment Station But. I76 l··~·· 1
ILr~\_.J I '~'-, \ I 1 u._ ..... f'l -~ r'- \ F' i \ ."-, ~I I I I "i 1 h-_. -.-I \ I I I __ Ji ...----1 .1 i 1 I I I I
Figure 8. The averace relative humidity in July at 2 p. m. for Wyoming. (After Atlas of American Agriculture). of the pest extending its range to other irrigated sections of the state during moist seasons. A climograph of temperature and moisture at Wheatland, when compared with the records of a region favorable to bean beetle development and dispersal, again shows that the Wyoming climate is unfavorable to the pest (Fig. 9). The annual rainfall at Wheatland is fourteen inches, while in one region favorable to the' pest the annual precipitation is nearly fifty inches. Con- sequently, with average moisture conditions at Wheatland, the insect is limited to the irrigated areas where the additional mois- ture changes the conditions from unfavorable to favorable sur- roundings during the summer months. This suggests the probabil- ity of the moist irrigated sections serving as centers of infestation that may be extremely important in years when climatic conditions become favorable for dispersal to the dry land communities. The principal bean growing area in Wyoming is the irrigated land in the Big Horn Basin in the vicinity of Powell, which has Jan. I931 The M esican Bean Beetle
80
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20'L.---~L---_±---_+---+---1:"5---7!6 234 PREPIPITAnON IN INCHES Figure 9. Climographs of Whealland, Wyoming, and weslern Soulh Carolina. Whealland annual precipitation 14.05 inches; western South Carolina annual precipitation 50.95 inches. an annual rainfall of 5.59 inches. Other irrigated regions where the bean crop is important are at Basin and Douglas, with 5.96 inches and 13-41 inches of precipitation annually. A comparison of the moisture conditions of these ections with those of Wheat- land shows that the bean beetle could not maintain itself without the aid of the additional moisture that is applied. The wide sep- aration of these bean growing communities may aid in protecting them from infestation by the pest, but the intervening spaces are not as difficult to overcome as the arid barrier between Fort Collins and "Wheatland. If once e tablished in the irrigated areas the bean beetle may prove to be very injuriou and could spread to the non-irrigated areas during moist seasons. 18 WY011'!ing Aqricultural Experiment Station Bul. I76
NATURAL CONTROL The Mexican bean beetle is rather free of natural enemies. None of the few can be depended upon to have any appreciable effect on the abundance and destruction of the pest. The weather is very important in controlling the dispersal and prevalence of the insect, as has been shown above. In the Southwest and West, moisture, which has been discussed above, is the principal limiting factor.
APPLIED CONTROL The best applied control known for the Mexican bean beetle is spraying with arsenical poisons. Apparently magnesium arse- nate, which is recommended by the United States Department of Agriculture, is the best material to use (Howard, 1930). A formula that has given satisfaction is one pound of the poison in fifty gallons of water, or, in smaller quantities, one ounce (five level tablespoonfuls) of the poison in three gallons of water. The spray mixture is prepared by placing the proper amount of the
A B c
Figure 10. The arrangement of nozzles necessary to spray the under sides of the leaves: A, for hand sprayers; B, C, for power sprays. (After Howard) , Courtesy of the U. S. Bureau of Entomology Jan. I931 The Mexican Bean Beetle 19 poison in a small quantity of water and washing it through a fine strainer to break up or remove coarse particles to prevent clogging of the spray nozzles. Since the pest ordinarily feeds on the under sides of the leaves the spray must be directed against the lower surfaces of the leaves to be effective. In order to do this, a nozzle arrangement such as shown in Figure 10 should be used. The nozzle used with hand sprayers are placed on a metal rod (Fig. 10, A), but with power prayers on wheels, the nozzles should be attached to the sprayer with hose connections (Fig. 10, B, C) in order to avoid breakage when spraying over rough or uneven ground. Dusts may be used instead of spray, but generally are not so effective. Magnesium arsenate is used as a dust in the pro- portion of one pound of poison to three pounds of hydrated lime and applied at the rate of fifteen to twenty pounds per acre. Dusting attachments such as those shown in Figure 11 should be used to place the dust on the lower surfaces of the leaves. A
Figure 11. Various r.ttachme nts to apply dust lnsectlcldes to the lower surfaces of the bean leaves. (After Jones). 20 WY01ning Aqricultural Experiment Statiow Bul. 176
A B c D Figure 12. Steps in shaping the home-made "spoon" device shown in Figure 11, from a piece of lin; (a) shows firsl step (circle is 17'2 inches in diameter); (b) cui gashes as shown; (c) fold lin as shown. '(d) The finished "spoon". (Afler Jones). home-made "spoon" built as shown in Figure 12 is very useful for hand dusters. The Colorado Experiment Station has reported good results with the use of zinc arsenite used at the rate of one pound to fifty gallon of water (Li t, 1921), It should be applied as di- rected above for magnesium arsenate. Lead arsenate, the common arsenical used on orchard trees, and Paris green, the common arsenical used on potatoes, should not be used on beans because of the danger of foliage burning.
CONCLUSIONS The Mexican bean beetle appears to be thoroughly established at Wheatland. The average moisture condition is the most im- portant single factor limiting dispersal and abundance, thus pre- venting the pest from spreading to the dry land farm areas. In- jury i noticeable and frequently severe in the irrigated district at Wheatland, showing that the insect is a potential danger to the bean growing industry if suitable climatic conditions develop. Insecticidal practices for control of the pest are given.
LITERATURE CITED Hepner, F. E., "Climatological Data for Wyoming," Wyo. Agr. Exp. Sta. Bul. 139 :1-160. (1924). Jan. 1931 The Mexican Bean Beetle 21
Howard, N. F .. "The Mexican Bean Beetle in the East and its Control," U. S. D. A., F. B. 1624 :1-14. (1930). Jones, 1\1. P., "The Mexican Bean Beetle," Ohio Agr. Ext. Bul, 75 :1-16. (1928). Kincer, J. B., "Precipitation and Humidity," Atlas of Amer. Agr. Part II, Climate: 1-..J-8. (1922). List, G. 1\1., "The Mexican Bean Beetle," Colo. Agr. Exp. Sta. Bul. 271 :1-58. (1921). Sweetman, H. L.. "Precipitation and Irrigation a Factors in the Distribution of the Mexican Bean Beetle, Epilaclma corrupta Muls,' Ecology 10 :228-44. (1929). "Ecological Studies of the Mexican Bean Beetle," Mass. Agr. Exp. Sta. Bul. 261 :1-32. (1930). 22 Wyoming Agricultural Experiment Station Bul. 176
The following bulletins of the Wyoming Experiment Station may be had upon request. (Revised list, February, 1931.) ANNUAL REPORTS- 19th to 39th, inclusive (1908-09 to 1928-29, inclusive). INDEX BULLETINS- C, D and E. HORTICUL TURAL BULLETINS- Special Bulletins, Volume I, Nos. 2 and 6. Biennial Reports, Thirds to Seventh, inclusive. No. STATE FARMS BULLETINS- 1. Spring Wheat Production in Eastern Wyoming. 2. Winter Wheat Production in Eastern Wyoming. 4. Some Results from Agricultural Stations over the State from 1923 Report. 7. The Service of the State Experiment Farms. No. CIRCULAR- 16. The Effect of Alkali on Portland Cement. No. BULLETINS- 92. The Value of Fiber Testing Machines for Measuring the Strength and Elasticity of Wool. 94. The Chemical Examination of Death Camas. 101. Zygadenine, the Crystallin Alkaloid of Zygadenus intermedius. 106. Cottonseed Cake vs. Cold Pressed Cottonseed Cake for Beef Cows. 110. Sweet Clover. 112. The Poisonous Properties of the Two-Grooved Milk Vetch (Astra- galus bisulcatus). 113. The Effect of Alkali upon Portland Cement. 115. Barley in Wyoming. 116. Winter Grains. 117. Cattle Feeding: Oat and Pea Silage for Beef Cows. Oat and Pea Silage for Growing Cattle. 118. Oats in Wyoming. 121. Swamp Fever in Horses. 128. Homegrown Feeds for Range Steers. 129. Sunflowers, their Culture and Use. 134. Wintering Range Calves. 135. Garbage for Fattening Pigs. 137. Wyoming Forage Plants and their Chemical Composition. 138. Experimental Transmission of Swamp Fever or Infectious Anemia 'by Means of Secretions. 139. Climatological Data for Wyoming. Jan. I93I The Mexican Bean Beetle
141. The Micrometer Caliper as an Instrument for Measuring the Dia- meter of Wool Fibers. 143. Chemical Examination of Three Delphiniums. 144. Lupine Studies II-The Silvery Lupine. 150. Fallow for Small Grains. 152. A Study of Potato Seed Treatment for Rhizoctonia Control. ISS. Type in Two-Year Old Beef Steers. 158. Use of Calcium Cyanide in the Apiary. 159. Surface Tension of Disinfecting Solutions for American Foulbrood. 160. Lessons from the University Dairy Herd. 161. Methods of Winter Wheat Tillage. 162. Making Bread from Wyoming Flour. 163. Results with Tree Planting at the Sheridan Field Station. 165: Dietary Studies of Farm Families in Albany and Lincoln Counties, Wyoming. 166. Sterilization of Brood Combs Infected with Ameriacn Foulbrood. 167. Field Studies of Physical Ecology of Alfalfa Weevil. 168. Soil Problems of Wheatland Project. 169. Artificial Incubation at High Altitudes. 170. Oat production and Varieties for Wyoming. 171. Varietal Tests with Wheat at the Sheridan Field Station. 172. Studies on Roup Vaccination in Chickens. 173. Methods of Spring Wheat Tillage. 174. Studies with Rambouillet Sheep II. 175. The Metabolism of the Honeybee Colony During Winter. Address requests: Bulletin Department, Experiment Station,