TECHNICAL BULLETIN NO. 88 MAY, 1929 TOBACCO CUTWORMS BY S. E. CRUMB Entomologist, Division of Truck-Crop Insects Bureau of Entomology LIBRARY! RECEIVED \ • AUG3 0 1929 •! UNITED STATES DEPARTMENT OF AGRICULTURE, WASHINGTON, D. C. 0. S. «OVEllliMElIT PI(IMT1N6 OFPlCBt Itt» TECHNICAL BULLETIN NO. 88 MAY, 1929 UNITED STATES DEPARTMENT OF AGRICULTURE • WASHINGTON, D. C TOBACCO CUTWORMS By S'. E. CRUMB Entomologist, Division of Truck-Crop Insects, Bureau of Entomology ^ CONTENTS Page Page -General consideration of tobacco cut- Consideration of the species 52 worms 1 The Feltia group __. 52 Distribution 3 The Euxoa group 86 Coloration of larvae 6 Genus Polia 115 Anatomy of larvae 7 The C-nigrum group 132 Outline for description of a cut- Genus Prodenia 142 worm 26 Remedial control of cutworms 156 Key to the cutworms which at- Poisons applied to plants 156 tack tobacco 26 Poisoned baits 158 Eggs and first-instar larvae 29 Other control methods 171 Pupae of tobacco cutworms 31 Literature cited 176 Breeding methods 33 Seasonal history 37 Natural control of cutworms 38 GENERAL CONSIDERATION OF TOBACCO CUTWORMS Tobacco is one of those crops, grown in plant beds and trans- planted to the open field, which are especially vulnerable to cut- worm attack.» Agricultural practice has accentuated its liability to injury by supplying conditions in the preceding crop (clover, grass, or weeds) which favor the multiplication of cutworms. With some types of tobacco it is desirable that all of the plants in a field ripen at about the same time. In such cases cutworm damage at trans- plajiting time may be unusually important. Cutworms differ in their method of attack and in the degree to which the cutting habit is developed. Thus Sidemia devastator ^ The investigation reported in this bulletin was conducted as a project of the then existing division of Southern Field Crop Insect Investigations. The writer wishes to express his appreciation of the helpful attitude shown hy A. C. Morgan, under whose direction the investigation was carried on. Several correspondents have given important assistance, especially C. N. Ainslie, J. U. Gilmore, D. C. Parman, and J. D. Mitchell. The authorities on insects in the Taxonomic Division of the Bureau of Entomology and in the National Museum have also rendered indispensable service. H. G. Dyar has been particu- larly helpful, and many of the data on the distribution of the species have been derived from an examination of the collections in his charge. Carl Heinrich has been of the greatest service in connection with the studies on larval anatomy. In the determination of the fungous diseases in the large number of larvae submitted to him, Alden T. Speare has nrade an important contribution. It is a pleasure to acknowledge the assistance given in a multitude of ways by the associates of the writer at the Clarksville laboratory. The writer wishes to express his appreciation of the willing and efficient service rendered by the bureau librarian, Miss Mabel Colcord. For illustrations the writer is indebted to the following : To H. B. Bradford for the drawings in Figure 4, D and B ; Figures 8, 9, and 10 ; Figure 13, A and B ; and Figures 14, 17, 18, and 19 ; to Joseph D. Smith for the draw- ings in Figure 4, A-C, F-J, and Figure 15, A-D ; to W. N. Dovener for the drawings of moths in Plate 2 and Plate 3 ; and to G. G. Ainslie for two photographs of eggs (pi. 4, B and C). 1431—29 1 1 TECHKICAL BULLETIN 8 8, U. S. DEPT. OE AGRICULTUKE feeds exclusively on the roots and adjacent stems of plants, whereas most species feed upon stems and foliage above ground ; Feltia an- nexa has developed a very characteristic habit of partially severing the leaves of large tobacco plants; and som^ species, such as Ewxoa Tnessoria^ Porosagrotis vetusta^ and Lycophotia saucio), have the climb- ing habit and sometimes feed extensively upon the buds and foliage of trees and shrubs. The restless destructiveness often shown by larvae of Ägratis ypsilon may be compared with the more conservative attack of larvae of Feltia gladiaria or of larvae of Prodeniá omitho- galU. The latter often feed upon foliage without resorting to the cutting habit. Some species, such as Feltia annexa^ Euxoa messoria^ and CKoriza- grotis {Euxoa) auxiliaris^ oviposit nearly or quite exclusively in cultivated fields, but cutworm damage is usu- ally most severe where tobacco follows clover or grass of several years' standing. Old pastures are also a pro- lific source of trouble when followed by to- bacco. Cutworms may occur in large numbers in such forage crops without attracting at- tention, and usually FIG. 1.—Outline map of the United States showing the tobacco-growing regions they are able to main- tain themselves indef- initely after the land is plowed. In rare instances such hordes of larvae are produced that they devour every green thing over large areas ; however, a greater aggregate loss is caused by ,the much less spectacular and often very local depredations of these larvae which occur every season. Twenty-two species of cutworms have been taken feeding upon tobacco in the field and are properly included in this bulletin. Three other common species are also included because they are general feeders and have been collected in tobacco-growing regions (fig. 1), making it highly probable that they will be found to injure this crop. Following are the species : Agrotis ypsilon Rott. Lycophotia (Peridroma) infecta Ochs. Agrotis l)adinodis Grt. (incivis Gn.). Agrotis c-nigrum L. Lycophotia (Peridroma) saucia Hbn. Agrotis unicolor Wlk. {clandestina Parastichtis (Amathea) 'bicolorago Gn. Harr. ). Polia (Mamestra) legitima Grt. Ghorizagrútis (Euxoa) auœiliaris Grt. Polia (Mamestra) méditât a Grt. Euxoa 'bostomensis Grt. Polia (MoAnestra) renigera Steph. Euxoa messoria Harr. Porosagrotis vetusta Wlk. (muraenula Euxoa tessellata Harr. G. & R.). Feltia annexa Treit. Prodenia dolichos Fab. (commieUnae Feltia ducens Wlk. S. & A.). Feltia gladiaria Morr. Prodenia eridania Cram. Feltia malefida Gn. Prodenia ornithogalU Gn. Feltia suhgothica Haw. 8idemia (Hadena) devastator Brace. Feltia veneraJ)ilis Wlk. TOBACCO CUTWORMS ó In this general consideration of tobacco cutworms those observa- tions are recorded which have a general bearing on the corresponding topics in the detailed treatments of the various species. DISTRIBUTION The data on distribution are still too meager to permit of exact delimitation of the range of tobacco cutworms, and the truth is fre- quently obscured by records of the occurrence of the volant adults far out of their real habitat, but as our knowledge of the distribution of the larvae increases it will be possible to define more clearly the true range of the species. Enough is now known, however, to permit of the statement that these insects conform rather closely in their distribution to the life zones of Merriam (4^).^ The following groups of species are to be distinguished : (1) The Transition and Upper Austral group. This group in- cludes the following 15 species: Feltia êucens^ F, suhgothica^ F, gladiaria^ F. venerabilis (probably), Porosa0rotis veticsta (prob- ably), Euœoa messoria^ E, tessellatm^ E, hostoniênsis (probably), Siderma devoMatoT^ Agrotis vmicolor^ A, hadinodisy A, c-mgnmi, Folia legitima (probably), P. Teni^ra^ and Pm'asticMis Mcolorago, (2) The Lower Austral group. This group includes the following five species: Feltia annexa^ F, Tnaleßda^ Prodenia ornithogaUi^ P, dolichos^ and P, eridama. (3) The western or arid-region group. This group includes but one species, Ohori^agrotis œmMiwris, (4) The eastern or humid-region group. This group includes Lycophotia infecta and PóUá meditata, Agrotis ypsilon also seems to have its metropolis in the northern part of this area. (5) The cosmopolitan group. This group includes two species, Lycophotia saucia and Agrotis ypsüorh^ and might also include Agrotis c-nigrv/m, LIMITING FACTORS IN THE DISTRIBUTION OF MULTIPLE-BROODED SPECIES The metropolis of most multiple-brooded species is in the warmer latitudes. This is largely due to their low resistance to cold in all their stages and to a tendency to pass the winter as pupae. Four of the multiple-brooded species have their metropolis in the north. Two of these, Polia renigera and Agrotis c-mgrmn, hibernate as larvae. Two cosmopolitan species, Lycophoüa saucia and Agrotis ypsiloriy pass the winter as pupae. Possibly these last species have become adapted to pupal hibernation owing to boreal origin. On the northern frontier of the range of a multiple-brooded species only a small î)roportion of the last brood of moths may succeed in pro- ducing overwintering progeny. This is due to the fact that each suc- cessive brood during the season emerges over a progressively longer period, with the result that in the later broods the period of emerg- ence is so extended that the progeny of the earlier moths produce other moths the same season too late for successful reproduction, while the progeny of the late-emerging moths are killed by the cold before reaching the pupal stage. 2 Reference is made by italic numbers in parentheses to " Literature cited," p. 176. 4 TECHNICAL BULLETIN 8 8, U. S. DEPT. OE AGRICULTURE This condition is exemplified in the case of Feltia annexa. About the earliest date of pupation which will result in overwintering pupae in this species is October 4. Pupae formed prior to this date produce moths the same season. For pupation after October 4 it is necessary that the parent moths 3haU not emerge earlier than about August 3. From somewhat meager data collected in 1913, 1914, and 1915 (1914 being unusually cold in November and the other two years mild) the writer concludes that the latest date of emergence which will allow the progeny time to reach pupation before being killed by the cold is prior to September 14.