The Relationship Between the Host Plant and the Dispersal of Larval Gypsy Moths, Lymantria Dispar (L.) (Lepidoptera: Lymantriidae)
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University of Massachusetts Amherst ScholarWorks@UMass Amherst Masters Theses 1911 - February 2014 1979 The relationship between the host plant and the dispersal of larval gypsy moths, Lymantria dispar (L.) (Lepidoptera: Lymantriidae). David R. Lance University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/theses Lance, David R., "The relationship between the host plant and the dispersal of larval gypsy moths, Lymantria dispar (L.) (Lepidoptera: Lymantriidae)." (1979). Masters Theses 1911 - February 2014. 3033. Retrieved from https://scholarworks.umass.edu/theses/3033 This thesis is brought to you for free and open access by ScholarWorks@UMass Amherst. It has been accepted for inclusion in Masters Theses 1911 - February 2014 by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. THE RELATIONSHIP BETWEEN THE HOST PLANT AND THE DISPERSAL OF LARVAL GYPSY MOTHS, LYMANTRIA DISPAR (L.) (LEPIDOPTERA: LYMANTRIIDAE) A Thesis Presented By DAVID R, LANCE Submitted to the Graduate School of the University of Massachusetts in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE September 1979 Department of Entomology THE RELATIONSHIP BETWEEN THE HOST PLANT AND THE DISPERSAL OF LARVAL GYPSY MOTHS, LYMANTRIA DISPAR (L.) (LEPIDOPTERA: LYMANTRI ID AE ) A Thesis Presented By DAVID R. LANCE Approved as to style and content by: Pedrp/, Barbosa, Chairperson of Committee David N. Ferro, Member T. MichaeA Peters, James B. Kring, Department Head /Department of Entomology ii ACKNOWLEDGEMENT I am deeply indebted to Dr. Pedro Barbosa, who made this work possible through his suggestions, criticisms, and support (financial and otherwise). I would like to thank Drs, David Ferro, T, Michael Peters, and Jane Greenblatt for their suggestions and careful reviews i of all or part of the manuscript. I also am indebted to the students, technicians, and lackies who worked in the insect ecology lab, most notably Wren Withers, Alex Segarra, and Bill Winnie, for their input into the project. Further, the entire crew of Feraaldites is to be thanked by one and all for the comradery which made even difficult times enjoyable. A number of people outside of entomology also made invaluable contributions to the project by helping me to maintain some shred of i sanity. Among these, I would especially like to thank Diane Boucher, whose efforts allowed me to get my mind off of insects at least on Wednesday nights, and, though she will never read this, Loosey, who remained my best friend throughout my stay here. Finally, a special thanks is due Debbie, whose loving support, which almost lasted the course of the project, kept my spirits up and provided goals when the hours were long and the rewords uncertain. iii TABLE OF CONTENTS ACKNOWLEDGEMENT...,...,,,.. iii LIST OF TABLES.,............ vi LIST OF FIGURES.,.,.,.vii Chapter I. INTRODUCTION...... 1 II. DISPERSAL OF LARVAL LEPIDOPTERA WITH SPECIAL REFERENCE TO FOREST DEFOLIATORS AND THE GYPSY MOTH... 4 Clarification of Terms.... 4 Dispersal in Lepidoptera....... 4 Orientation to Physical Stimuli,.... 7 Abiotic Factors Affecting Dispersal,.. 9 Diel Rhythms...... 11 Biotic Factors Affecting Dispersal.... 13 Natural enemies..... 13 Limiting resources and density-dependent factors,. 15 Host selection as it affects dispersal. 23 Host orientation by lepidopterous larvae.. 25 Host acceptance by lepidopterous larvae... 27 Habitat Stability, Host Predictability, and Dispersal: " 31 Implications for Forest Tree-Feeding Lepidoptera and the Evolution of Flightlessness.,..... 31 III. THE RELATIONSHIP BETWEEN THE HOST PLANT AND THE DISPERSAL OF FIRST INSTAR GYPSY MOTHS,. .. 35 Introduction... 35 Materials and Methods...... 38 Laboratory tests....*.. 38 Field trapping......... 42 Relative density on different hosts,.,,.. 43 Results... 44 Laboratory tests.......... 44 Field trapping... 46 Relative density.. 51 Discussion and Conclusions. 52 IV. THE RELATIONSHIP BETWEEN THE HOST PLANT AND THE DISPERSAL OF LATE INSTAR GYPSY MOTH LARVAE. 56 Introduction. 36 iv Materials and Methods........ 58 Field studies. 58 Laboratory studies..... 59 Source of larvae...... 59 Larval activity rates. 60 Orientation of larvae... 61 Results... 61 Field studies. 61 Laboratory studies........ 73 Activity rates............ 73 Orientation.......... 76 Discussion and Conclusions...... 78 LITERATURE CITED......... 83 v « LIST OF TABLES 1. Dispersal of gypsy moth larvae in the laboratory in the presence of apple or hemlock foliage . 45 2. Dispersal in the laboratory of gypsy moth larvae from large eggs in the presence of several hosts commonly encountered in New England forests . 47 3. Dispersal of gypsy moth larvae in the laboratory in the presence of red oak and red maple . 48 4. Larvae resting under burlap bands at Sturbridge, MA, in 1977 . 62 5. Larvae resting under burlap bands at Spencer, MA, in 1977 . 63 6. Activity of field collected fifth instars in the presence of red oak, red maple, and manually defoliated red oak. 74 7. Activity of laboratory-reared fifth instars in the presence of red oak, red maple, and paper leaf models .. 75 8. Influence of size on the orientational responses of fifth instars . 77 vi LIST OF FIGURES 1. First instar field traps . 41 2. Larvae captured leaving trees as a function of the number of larvae coming to the trees in Sturbridge, MA, in 1977 . 49 3. Larvae captured leaving trees as a function of the number of larvae coming to trees in Spencer, MA, in 1977 . 50 4. Number of larvae captured under burlap bands on black cherry as compared to all other species at Sturbridge, MA, in 1977 . 65 5. The logarithmic decay of marked larvae from different tree species at Sturbridge, MA, in 1977 .. 67 6. The logarithmic decay of marked larvae from different tree species at Spencer, MA in 1977 . 68 7. The logarithmic decay of marked larvae from trees of different sizes in Sturbridge, MA, in 1977 .. 69 8. The logarithmic decay of marked larvae from trees of different sizes in Spencer, MA, in 1977 .. 70 9. Logarithmic decay of marked larvae from all trees at Sturbridge, MA, compared to the decay of marked larvae from all trees at Spencer, MA, in 1977 .. 71 10. The logarithmic decay of larvae from a large red oak with deeply furrowed bark compared to the decay from other trees at Spencer, MA, in 1977 . 72 vii 1 CHAPTER I INTRODUCTION The gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae) is a pandemic species which feeds on the foliage of numerous forest and shade trees. It was introduced into north America in 1869 at Medford, Massachusetts by Leopold Trouvelot, a French naturalist experimenting with silk production (Forbush and Fernald 1896). The range of the gypsy moth has spread at a rate of 9.6 kilometers per year against prevailing winds and now covers most of the northeastern United States (McManus 1973a). Other infestations have developed in such distant areas as Michigan, California, and Washington, probably due to human transportation of pupae or eggs. Initial infestation of the species is characterized by widespread defoliation of trees over a period of several years. Mortality of trees, especially favored species, may result (Baker 1941). Populations then decline to a lower (endemic) level, with little noticeable defoliation. Endemic populations will occasionally return to outbreak levels, but the length of the outbreak phase and the total area affected are usually somewhat reduced from those observed in the initial invasion. Larvae normally pass through five (male) or six (female) instars, but extra-instar individuals are not uncommon, especially under crowded conditions (Leonard 1968X. They then pupate on the boles or branches of trees, in the litter or on other available objects on the forest floor. Adults emerge in about two weeks and mate, and females lay their entire compliment of 30-1000 eggs in a single mass near their pupation site. 1 2 The species is univoltine throughout its range. Eggs hatch the following spring, typically soon after budbreak to most forest trees. The egg hatch to oviposition period is two to three months. Adult females are fully winged, but in North America and western Europe they are incapable of flight. Dispersal is accomplished by the larvae. After hatching, first instars climb to terminal branches, drop on silk threads, and may be carried by the wind for distances ranging from several centimeters to several kilometers (Burgess 1913; Collins 1915; Collins and Baker 1934). Aerial buoyancy is aided by the silk and by their numerous hairs, which effectively increase their surface-to-volume ratio CBurgess 1913). Although dispersal of later instars is much more limited in the distance covered, they are capable of redistributing populations within a locale. The gypsy moth is highly polyphagous. Of 477 potential food plants tested by Forbush and Fernald (1896), 458 were accepted by larvae. How¬ ever, survival and a number of developmental parameters are optimized when larvae concentrate their feeding on a restricted number of more suitable species such as the oaks, Quercus spp. (Mosher 1915; Hough and Pimentel 1978; Barbosa and Greenblatt, in press). Thus finding a highly suitable host would be advantageous to the dispersing larvae. While most, if not all, first instar gypsy moths disperse, they are passively dis¬ persed and cannot direct their flight toward a specific plant. They can only select their hosts by settling on more preferred species and not exposing themselves to wind currents. The degree to which larvae select hosts in this manner is investigated in this paper. 3 While first instars are active only during the photophase, older larvae (instars IV-VI) are nocturnal and seek protected resting sites on trees or in the litter by day. This behavior changes as larval density increases, with older larvae also remaining active throughout the photophase. As 60-80% of the feeding occurs in the last instar (Leonard 1974), the dispersal of late instars to and from various host plant will have profound effects on parameters such as pupal weight and fecundity (Barbosa and Capinera 1977; Capinera and Barbosa 1977).