'-----_.- / BULLETIN NO. 176 ,z.... JANUARY, 1931 UNIVERSITY OF WYOMING AGRICUL TURAL EXPERIMENT STATION The Mexican Bean Beetle 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.