Research Collection Habilitation Thesis Spiders as biological control agents in cotton plantations in Texas Author(s): Nyffeler, Martin Publication Date: 1996 Permanent Link: https://doi.org/10.3929/ethz-a-005794601 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library SPIDERS AS BIOLOGIGAL CONTROL AGENTS IN COTTON PLANTATIONS IN TEXAS HABILITATION THESIS submitted to the Faculty of Science, University of Bern to obtain the Venia Docendi presented by MARTIN NYFFELER Dr. sc. nat. ETH citizen of Huttwiln Ganton Bern, Switzerl. born on March 25, { 95O Submitted: April 27, 1995 Accepted: January 26, {996 Eduotion r Resarch . Extension TEXAS A&M UNIVERSITY College of Agriculture and Life Sciences Department of Entornology April 5, 1994 To Whom It May Concern: Dr. Martin J. Nyffeler, formerly associated with the Entomological Institute, Swiss Federal Institute of Technology, Zurich, worked in my laboratory from 1985-86 (as a postdoc on a f ellowship of the Swiss National Science Foundation) and f rom 1988-94 (as a visiting scientist). In association with my laboratory he conducted postdoctoral research on the significance of spiders as biocontrol agents of insect pests. He conducted field work in insecticide-free cotton agroecosystems in Austonio, east Texas (summer 1985) and in Snook, central Texas (summer 1988). Later he conducted extensive literature research for several review papers. More recently he wrote a statistical-mathematical paper that has been accepted by Environmental Entomology (Entomological Society of America). The results of research in which he was involved as a principal investigator or collaborator have been published in over 20 papers in various international and national scientific journals during his stay at my laboratory. Two extensive review papers on the predation ecology of spiders are currently in preparation. - Dr. Nyffeler asked for permission to use the data (from his field and review research) collected during his postdoctoral work at Texas A&M University for a "Thesis of Habilitation" to be submitted to a university in Europe in order to obtain the qualification of the "habilitation." I hereby grant Dr. Nyffeler permission to use these data for a "Thesis of Habilitation" and I am pleased to lend support to his case. Sincerely, h/-#'UW;-. ,q. ,4t ,,zz- winf fletO L. Sterling tr Professor Emeritus Entomology Reeeerch hboratory Teras A&M University College Station, Texas 78Al-2475 (409) 845-3411 FAX (409) 847.8668 Table of Contents Page I TABLE OF CONTENTS: I SUMMARY 2 GENERAL INTRODUCTION 3 PREY SELECTION AND PREDATORY IMPORTANCE OF ORB.WEAVING SPIDERS (ARANEAE: ARANEIDAE, ULOBORIDAE) IN TEXAS COTTON. (Environmental Entomology 18: 373-380 t19891) PREDATION BY GREEN LYNX SPIDER, PEUCETU VINDANS (ARANEAE: OXYOPIDAE), INHABITING COTTON AND WOOLLY CROTON PLANTS IN EAST TEXAS. (Environmental Entomology 16: 355-359 [1987]) l4 EVALUATION OF THE IMPORTANCE OF THE STRIPED LYNX SPIDER, OXYOPES SALTICUS (ARANEAE: OXYOPIDAE), AS A PREDATOR IN TEXAS COTTON. (Environmental Entomology 16: I 1 14-1123 t19871) 19 DIETS, FEEDING SPECIALIZATION, AND PREDATORY ROLE OF TWO LYNX SPIDERS, OXYOPES SALTICUS AND PEUCETIA VIRIDANS (ARANEAE: OXYOPIDAE), IN A TEXAS COTTON AGROECOSYSTEM. (Environmental Entomology 2l: 1457 -1465 $9921) IMPACT OF THE STRIPED LYNX SPIDER (ARANEAE: OXYOPIDAE) AND OTHER NATURAL ENEMIES ON THE COTTON FLEAHOPPER PSEUDATOMOSCELIS SERATUS (HEMIPTERA: MIRIDAE) IN TEXAS COTTON. (Environmental Entomology 21: II78-1188 I19921) 38 COMPARISON OF THE FEEDING NICHE OF POLYPHAGOUS INSECTIVORES (ARANEAE) IN A TEXAS COTTON PLANTATION: ESTIMATES OF NICHE BREADTH AND OVERLAP. (Environmental Entomology 23: 1294-1303 t19941) 49 9 HOW SPIDERS MAKE A LIVING (FORUM-article). (Environmental Entomology 23: 1,357-1367 119941) 59 10 GENERAL DISCUSSION 70 11 FINAL CONCLUSIONS 77 t2 ZUSAMMENFASSUNG 78 Chapter 1: Summary Page 2 SUMMARY The ecological impact of spider predation on cotton insects in cotton fields in Texas was investigated. In particular, it was assessed how frequently the spiders feed on four 'key pests' of Texas cotton (i.e., cotton fleahopper Pseudatomoscelis seriatus [Heteroptera: Miridae], boll weevil Anthonomus grandis grandis [Coleoptera: Curculionidae], bollworm Helicoverpazeaf: Heliothis zeallLepidoptera: Noctuidael, and tobacco budwormHeliothis virescens [Lepidoptera: Noctuidael) and to what extent this may impact the mortality of these pests. The data were collected over a period of totally = 2OO h of visual observations in the course of two field projects: The first project was conducted during the summer of 1985 in an unsprayed (6.5 ha) cotton plantation near Austonio, Houston County, East Texas. The second project was undertaken during the summer of 1988 in an unsprayed (13.6 ha) cotton plantation located near Snook, Burleson County, Cenfral Texas, approximately 100 km southwest of the previous study site. The spider assemblages found in cotton in Austonio and Snook were quite similar and represent a species complex typical for extensive cotton growing areas throughout the U.S. cotton belt, with lynx spiders (Oxyopidae) numerically predominating. Lynx spiders consistently constituted > 50% of the spider total throughout the growing season. The second most abundant spider group, the orb-weavers (Araneidae and Tetragnathidae), constituted = l0% of the spider total. Two species of lynx spiders occur in these f,relds: the 'striped lynx' Oryopes salticus and the 'green lyru.' Peucetia viridans. The numerically dominant Oryopes occurred in average densities of - 1-1 .slmt during mid-season in both plantations . I Peucetia is less frequently found in cotton and is therefore expected to be of minor importance as a potential natural enemy of pests in the cotton fields. I The studies focussed primarily on the numerically dominant lynx spiders and orb-weavers. To evaluate the predatory significance of the lynx spiders relative to the other predaceous arthropods occurring in cotton, the total number of predation events observed athibutable to lynx spiders versus other arthropod predators was compared based on the data which had been collected in Snook. A total of 134 arthropod predators with prey in their chelicerae/mandibulae were monitored during the 108 h observation period, which included 94 lynx spiders versus 40 other predators. Thus, 70Vo of all predation events observed were attributable to lynx spiders which indicates that these spiders were the dominant predators in this cotton plantation. Similar patterns of a predominance of lynx spider predation were observed in Austonio, too. The predation rate (: no. prey killed/spider/day) was estimated with a visual method based on average feeding frequency (percentage spiders with prey in their chelicerae) observed in the field, average handling time, and hunting (searching) time; it was estimated that a subadult/adult Oryopes (representing a typical agroecosystem spider) may capture : 1 prey organism on an average rainfree day in the field (during the middle of the growing season). The same spiders feed at several times higher rates in laboratory feeding experiments if food is offered ad libitum (as is known from literature), which suggests that in the field these spiders often feed below their maximum feeding capacity. Thus, the spiders can be expected to increase their predation rate during severe outbreaks of insect pests (i.e., 'functional response'). Chapter l: Summary Page 3 Themajorityof thelynxspidersincottonwereof smallsize (i.e.,Oryopes). Oryopes captures a wide variety of small-sized arthropods ranging from 0.6 to 6 mm length ( = 2.5 mm optimal prey length). I In confrast to this, the larger Peucetia feeds over a broader range of prey size classes and consequently captures a higher proportion of the larger prey organisms, but because this species is much less abundant than Oryopes, its contribution to the overall predation impact is rather low. I Likewise, most orb-weavers occurring in cotton were of small body size. Overall, spider individuals of small size (including large percentages of immatures) numerically dominate the faunas of the investigated cotton fields, and these spiders feed primarily on tiny prey organisms (< 3 mm in length). With a body length range of l.l-2.9 mm (third instar to adult) cotton fleahoppers ideatly fit the optimal prey length of = 2.5 mm for Oryopes. f Peucetia, that captures on the averagä significantly larger-sized prey than Oryoper, seems to be less efficient in capturing fleahoppers.l Oryopes shows considerable flexibility in switching its feeding patterns in response to prey availability. - In the cotton plantation in Austonio, the numbers of cotton fleahoppers were below the economic threshold, and consequently very low predation rates on fleahopper prey by spiders were observed (0% fleahoppers in the diet of Oryopes); instead, Oryopes fed heavily on red imported fire ants (22% of the diet) and other nonfleahopper prey. - A totally different scenario was observed in the cotton plantation in Snook, where cotton fleahoppers occurred in fairly high numbers; in this situation, Oryopes fed heavily on these pests (fleahoppers constituting 24% of the diet). - These data indicate that Oryoper may feed heavily on other predators such as fire ants when pests are rare; however, when pests become abundant this spider can largely switch to pestiferous species