Texas Citrus Research Articles

Factors Affecting Biological Control of Scale Insects on Texas Citrus1

Biological control of citrus insects has been an important economic consideration in the Lower Rio Grande Valley citrus area during the past 20 years. Many growers who applied chemicals to control scale insects on an extensive basis found that their neighbors who used no chemical sprays profited as well and did not upset a predator-pest relationship in nature. Yearly spray operations seemed necessary once the grower started spraying. Other pests, for which the man did not spray, often developed to damaging numbers. Growers, thus, directed chemical control efforts against the two most important pests: the citrus rust mite, Phyllocoptruta oleivora (Ashm.) and Texas citrus spider mite, Eutetranychus banksi McG. At the present time, sprays are not commonly used in the area and dusts are the common means of applying chemicals for the control of these pests.

Eutetranychus banksi (McG.) Recently Found on Citrus in Florida (Acarina: Tetranychidae)

In November, 1951, a series of specimens of this unusual spider was collected from a moderately infested orange grove one mile east of Scottsmoor, Florida, in Brevard County. As Eutetranychus banksi (McG.), 1914, was known previously only from castor bean and velvet bean, the species was tentatively identified by the senior author as E. clarki (McG.), 1935, and specimens were sent to Dr. E. W. Baker of the United States National Museum for confirmation. Dr. Baker identified the species as E. banksi (McG.) and stated in correspondence that banksi and clarki appeared to be the same species with the dorsal setal pattern being quite variable. As E. mexicanus (McG.), 1950, was segregated from clarki by McGregor primarily on the basis of dorsal setal variation it appears that all three names must be considered synonymous. Eutetranychus banksi (McG.) is the older name and therefore should be used for this variable, widely distributed species. McGregor (1935) established the common name Texas citrus mite for clarki which probably should be retained for banksi because of the common occurrence and economic importance of this species in Texas, Mexico and Costa Rica. In making the above synonymic analyses several hundred specimens were examined. Material representative of E. banksi (McG.) was collected by the authors from citrus in two areas in Florida. Specimens representative of E. clarki (McG.) and E. mexicanus McG. were collected by Dr. A. F. Camp from citrus in Costa Rica. All specimens were mounted in Hoyer's modified Berlese solution for microscopic examination. Taxonomic descriptions of the species have been published by McGregor (1914, 1935 and 1950). A good general description of the living mites was given by Dean (1952). The eggs of the species are flat and disc-like with a fine, rolled rim or edge as shown in figure 1. They vary in color from light yellow when laid through tan and green to reddish-brown just prior to hatching. Newly hatched larvae are light yellow to tan with pale legs. Nymphs, except for size, appear much like the adult females in form and color. Adult females are slightly larger

INORGANIC COMPOSITION OF EXUDATE FROM EUREKA LEMONS TREATED WITH ELEMENTAL SULFUR DUST

IN STUDIES ON the physiological effects of elemental sulfur dust on citrus fruits (Turrell, 1950), it was noted that at temperatures of 105?-140?F. both nondusted and sulfur-dusted lemons contained in pyrex bottles through which a stream of washed air was passed yielded a yellow liquid. Because of the experimental conditions imposed on the fruit, the liquid might be considered a condensate, but it was observed in these studies, as in early stages of sulfur burn, that the affected area usually developed a translucent appearance. This has been interpreted as indicating an exudation (leakage sap) of the cell solution into the intercellular spaces of the mesocarp, a condition likewise developing when citrus fruits are incubated in closed systems. Perhaps the yellow liquid thus formed mav be correctly described as both a condensate and an exudate: the first because the containers were visibly covered with droplets of moisture, and the second because of the large number of nonvolatile constituents found in the qualitative analysis (Turrell, 1950) and the translucent appearance of the fruit peel. The term exudate is preferred, however, and is used throughout this report. The condensate is considered as an unavoidable contaminant. Exudation, apart from dew formation, has not been observed generally in citrus under field conditions in California. Deposits have been observed on foliage leaves of citrus in Texas, however, by Ivanoff (1941). This finding suggests that exudation or guttation in citrus may occur under natural growing conditions. The organic and inorganic constituents in exudates of nondusted and sulfur-dusted lemons are of interest because they may be indicative of the effects of elemental sulfur dust as compared with those of heat. Since no qualitative differences have been found in the exudates of such fruit, but a difference in specific gravity has been observed (Turrell, 1950), a quantitative study of the inorganic and organic composition of exudates from intact Eureka lemons was undertaken. The present report concerns the inorganic constituents. REVIEW OF LITERATURE. Numerous chemical analyses of exudation or guttation fluids of intact plants have been made. De Saussure (1804) appears to have been one of the first to analyze the deposit left by the exudates evaporated from leaf surfaces. At the time of his study the injury caused by or associated with the incrustation left by evap-

Spider Mites of Citrus and Texas Citrus Mite Control in the Lower Rio Grande Valley of Texas

Spider Mites of Citrus and Texas Citrus Mite Control in the Lower Rio Grande Valley of Texas