Factors influencing the population dynamics of brown soft scale, Coccus hesperidum L. in South Texas.
| Main Author: | |
|---|---|
| Other Authors: | , , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1983.
|
| Subjects: | |
| Online Access: | Link to ProQuest Copy Link to OAKTrust copy |
| Abstract: | The brown soft scale in South Texas is usually controlled by a complex of parasites. Observations made over a ten year period showed that the scale was disrupted by drift of ethyl and methyl parathion from applications made to control cotton pests. The most significant disruption occurred in the middle portion of the Lower Rio Grande Valley where plantings of cotton and citrus are widely interspersed. Some cotton in the mid valley area received up to 30 applications of ethyl and methyl parathion during the growing season. Studies demonstrated that not only did the parathion decimate the parasite population but that there was also a stimulatory effect on the reproductive rate of brown soft scale. The problem was unique in the Lower Rio Grande Valley because the pesticide disruption was due to applications on another crop, prevailing winds consistently reached 13 to 15 mile per hour and the pesticide applications were almost totally aerially applied. Parathion was the only pesticide implicated in this biological upset. Fecundity studies of brown soft scale demonstrated that this parthenogenetic species produces more offspring over a longer period of time than had been recorded in any previous investigation. One female lived for 215 days and produced young for 211 days. Another scale produced almost 4000 offspring during its reproductive period. Despite the persistent decline in parasite populations that occurred each spring and the sharp increases in brown soft scale that followed, parasites at some point during the year usually reduced the scale to considerably lower densities. A complex of parasites was usually responsible and the composition of this complex changed with time. Coccophagus lycimnia (Walker) usually dominated the complex but at certain times during the year other species became predominant. Microterys flavus Howard was the second most important parasite early in the study but more recently was surpassed by Metaphycus flavus Howard. Comparable successions were also reported from other parts of the world. Throughout a 14 year period twenty parasites were introduced from various locations around the world. Although several species showed up in subsequent collections there appears to be no evidence of a significant impact by any of the released parasites. Detailed studies of Microterys flavus from various geographical locations showed variation in fecundity, rates of parasitism and host feeding. These studies also showed that brown soft scale from different areas have differences in capability to encapsulate parasite eggs. |
|---|---|
| Item Description: | "Major subject: Entomology." Typescript (photocopy). Vita. |
| Physical Description: | xii, 125 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references (leaves 114-119). |