THE SOUTHWESTERN CORN BORER IN ARKANSAS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By LAWRENCE HUBERT ROLSTON, A.B., M.S. The Ohio State University 1955 Approved by: Department of Zoology and Entomology ACKNOWLEDGMENTS The author is particularly indebted to; Dr. Ralph H. Davidson, of The Ohio State University, and the staff of the Department of Entomology at the University of Arkansas for suggestions during the course of this investigation and critical reading of the manuscript; to student assist­ ants Messrs. Philip Callahan, James Hawkins and Ralph Mayes; to Mr. Henry Vose, Manager of the substation at Van Buren for his cooperation; and to Dr. Lloyd 0. Warren for the photography. A special expression of gratitude is due the many farmers who tolerated trespassing, mutilation of their corn and other nuisances. ii TABLE OP CONTENTS Introduction ......................................... 1 Review of Literature Dlatraea species In the United States ............ 2 History and distribution ........................ 3 Life and Seasonal History Life history .................................... 8 Seasonal history ................... 8 Description of Injury ................................ 13 Adult Description ..................................... 17 B e h a v i o r ........................................ l8 Emergence ....................................... 20 Longevity ....................................... 20 Proportion of sexes ............................. 22 Mating .......................................... 23 Oviposltion....... 24 Fecundity and fertility............... 23 Oviposltion preference ....................... 26 Flight range .................................... 28 Light ........................................... 31 Egg Description........... 32 Location of eggs ................................ 33 Development and Incubation ...................... 33 Eclosure ......................................... 34 Larva Description..................................... 33 Pall activity ................................... 36 Survival of overwintering brood ................. 4l Spring activity ................................. 42 Number and duration of Instars .................. 42 Larval position on corn ......................... 46 Prepupa ............ 32 Pupa Description..................................... 32 Duration of pupal stage ......................... 34 Hosts Other Than Corn ................................ 34 Natural Enemies ...................................... 60 111 Control Methods Cultural control ................................ 62 Insecticidal control ............................ 63 S u m m a r y ............................................. 67 Literature Cited .................................... 69 LIST OP ILLUSTRATIONS I, Distribution of the southwestern c o m borer In Arkansas ............................. 7 II, Emergence of the principal broods at Fayetteville and Van Buren, 1952-54 ......................... 13 III, Female of the southwestern c om borer ........... I9 IV, Girdled stalk .................................. 37 V. Overwintering larva In base of s t a l k ............ 38 VI. Distribution of 1,365 field collected larvae according to head capsule width ................ 47 Iv Introduction In the brief interval following the entrance into Arkansas of the southwestern c o m borer, Diatraea grandio- aella Dyar, it has become a c o m pest of great importance. A thorough investigation of the biology and possible control measures was necessitated by the rapidity with which the borer has spread and the resulting crop damage. Reduction of yield arises in several ways. Young plants may be killed or dwarfed by borer activity in the stem; the yield may be reduced by extensive tunnelling in the stalk; and mature grain may be lost as a result of fall girdling activity. Heavy infestations in sweet corn ears, although infrequent, are disastrous to the grower when they occur. Relatively little has been published about the south­ western c o m borer in spite of its economic importance and of its having been in the United States for many years. The first comprehensive investigation was that of Davis and his co-workers in New Mexico and Arizona (2). More recent bul­ letins have been issued by Kansas (13) and Oklahoma where particular attention has been paid to the development of cultural control practices (14). Since Arkansas differs considerably in climate and to­ pography from the locales of previous investigations, there was no assurance that the seasonal history of the borer would parallel that in neighboring states or that cultural 2 practices recommended there would be effective under Arkansas conditions. The biology of the borer has been given particular at­ tention during this investigation. The habits of both the larva and adult have been studied to ascertain the possibili­ ties they offer for control as well as the limitations they impose. Previously suggested cultural control measures have been evaluated under local climatic conditions. Review of Literature Diatraea species in the United States The genus Diatraea contains a large number of species but nearly all are confined to tropical and subtropical re­ gions. Several species are important pests as borers in cul­ tivated grasses, particularly sugar cane and corn. Of the six Diatraea species known from the United States, three are apparently rare and of no economic importance: D. evanescens Dyar, D. lisetta (Dyar) and D. venosalis (Dyar). The sugar cane borer, D. saccharalis (Pabr.), is well known as a pest of both sugar cane and com. It is found along the Gulf Coast of Texas, Louisiana and Mississippi and in the southern half of Florida. The southern corn stalk borer, D. crambidoides (Grote), is capable of damaging c o m severely but is not consistently a major pest. Its range extends from Maryland to Florida and apparently westward into Kansas but heavy populations 3 are confined to the southeast. This species is widely known under the synonym D. zeacolella Dyar. The southwestern c o m borer, D. grandioaella Dyar, con­ cludes the list of known Diatraea species from the United States. The range of this insect and the damage caused are discussed in detail under appropriate sections. yet another species, D. lineolata (Walker) has been er­ roneously reported from the southwest. Until 1911 D. saccharalis (Pabr.) was believed to be the sole representative of the genus in the United States and all papers and records on the southern c o m stalk borer and south- westem corn borer, as well as the sugar cane borer, were pub­ lished under this name. In that year Dyar published a revi­ sion of the Diatraea based on the color and extemal morphology of the adult but the characters used have proved Insufficient to consistently separate all the species (3). The main im­ pact of this paper on economic literature was the establish­ ment of the southern c o m stalk borer, under D, zeacolella Dyar, as a species distinct from the sugar cane borer of southem Florida and the Gulf Coast. Holloway later gave a method for distinguishing the larval forms of these two spe­ cies by means of the setal pattem (7). In Dyar's revision, the southwestem c o m borer was described as a new species from Mexico and D. lineolata (Walker) was redescribed from specimens from Mexico and a single specimen from Arizona. This latter specimen was undoubtedly not D, lineolata (Walk.) 4 but the southwestern c o m borer, for the northern limit for D. lineolata (Walk.) Is now known to be central Mexico (1). The revision of Dyar and Heinrich In I927 has done much to clear up the confusion concerning the identity of Diatraea species (6). As a result of these authors' detailed study of the genitalia for diagnostic purposes there was a complete change In species concepts, many names being reduced to syn­ onymy and others recognized as valid. References to Diatraea species prior to 1927, and par­ ticularly those before 19II, must be regarded critically. Sometimes the Identity of the species involved can be deduced from the locality. Adequate descriptions of habits, damage and the egg are of great help, of the three common Diatraea the sugar cane borer Is the only species not habitually over­ wintering In the stalk base below soil level. The eggs of the southwestern corn borer are distinctive, having three red bars that the eggs of the other two species lack, and the larva's habit of girdling the stalk near ground level In the fall Is unique. For a technical description of American Diatraea, along with excellent drawings of the genitalia, the reader Is re­ ferred to Dyar and Heinrich (6), In this paper D, lisetta (Dyar) Is described and figured under the synonym lesta li­ setta Dyar and D, crambidoides (Grote) under D, zeacolella Dyar, 5 The synonymy of American species and new species, as well as photomicrographs of genitalia, are given by Box (1). History and distribution What may be the first reference to the southwestem c o m borer occurs In a note appended to a paper by L. 0. Howard In 1891> stating that larvae of the sugar cane borer had been found Infesting c o m In two localities In New Mexico (8), These larvae were probably the southwestem c o m borer, since It Is the only Diatraea species normally found In this area. The distribution In 1931, as given by Davis et al.. Included southeastem Arizona, the southeastern two-thirds of New Mexico, most of the Panhandle and Big Bend of Texas, most