Thesis (MSc)--Stellenbosch University, 1992. / One copy microfiche. / ENGLISH ABSTRACT: The effects of synthetic pyrethroids on the spider mite, Tetranychus urticae Koch, and its natural enemies was investigated. The pyrethroid cyfluthrin, sprayed for the control of fruit weevil Phlyctinus callosus, did not cause mite outbreaks and was not harmful to the predators when sprayed before they appeared on the apple trees. This spray also gave good control of thrips, bollworm (Heliothis armigera) and fruit weevil (P. callosus). A late season spray of deltamethrin against codling moth, caused an increase in the phytophagous mite population. This was assosiated with a temporary reduction in the population level of the predatory beetle, Oligota fageli. The plants found on the orchard floor were examined. The plant diversity was low and plants that acted as hosts of phytophagous mites during the winter were scarce. However, Solanum nigum carried high mite populations and infected the adjacent apple trees. The plants were too few to have an effect on the whole orchard. Eight synthetic pyrethroids were tested for repellency in a leafdisk dip and spray bioassay using T. urticae. Deltamethrin and fenvalerate caused no walk-off. Cyfluthrin and fluvalinate caused moderate walk-off and bifenthrin, cyhalothrin and lambda-cyhalothrin caused high walk-off. / AFRIKAANSE OPSOMMING: Die invloed van sintetiese piretroIedes op die rooispinmyt, Tetranychus urticae Koch en hul natuurlike vyande is ondersoek. Die piretroIed, cyfluthrin, gespuit vir die beheer van snuitkewer, P4ctinus callosus, het the mytuitbrake veroorsaak the en was ook the skadelik vir predatore nadat dit vroeg in die seisoen, voordat myte in die appelbome verskyn het, gespuit is the. Die bespuiting het ook goeie beheer van blaaspootjies, bolwurm (Heliothis amdgera) en P. callosus gegee. Deltametrien wat later in die seisoen toegedien is vir die beheer van kodlingmot, Cydia pomonella, het 'n mytuitbraak veroorsaak. Dit word geassossieer met die tydelike onderdrukking van die populasievlak van die predatoriese kewer, Oligota fageli. Die plante in die dekgewas is ondersoek. Die plant-verskeidenheid was laag en plante wat kon dien as oorwinterings gashere vir fitofage myte kon dien was skaars. Solanum nigrum het egter groot bevolkings myte gedra wat die appelbome naaste aan hulle eerste besmet het. Daar was egter te min van hierdie plante om 'n invloed op die hele boord te he. Agt piretroIedes is vir afwering van T. urticae in 'n blaarskyf doop en spuit bioessal getoets. Deltamethrin en fenvalerate het geen afwering getoon the. Cyfluthrin en fluvalinate het 'n redelike afwering, terwyl bifenthrin, cyhalothrin en lamda-cyhalothrin het 'n hod mate van afwering getoon

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The overall goal of this research was to determine the effects of spirea aphid, Aphis spiraecola Patch, feeding and nitrogen fertilization on net photosynthesis (Pn), leaf chlorophyll content and greenneess, growth, dry matter accumulation, and carbohydrate concentrations of young apple trees, with comparisons to apple aphid, Aphis pomi DeGeer. Trees were artificially infested and grown in an unheated greenhouse with screened ends. The spirea aphid responded differently to various nitrogen treatments. Aphid density increased at a faster rate on trees receiving higher nitrogen application. The leaf nitrogen concentration increased significantly and linearly with increasing amount of urea application in both infested and control leaves. Also, a significant difference in leaf nitrogen concentration was found at each urea application rate between infested and control leaves. Spirea aphid feeding and sooty mold accumulations caused significant reductions in photosynthetic rates, leaf chlorophyll content, and greenness. Pn increased linearly with increasing chlorophyll content and greenness; nitrogen rates caused an increase in Pn and leaf greenness. Aphid-days accumulations were strongly correlated to Pn and greenness at each nitrogen rate applied. Accumulation of callose at the phloem sieve plates in response to spirea aphid feeding occurred but to a lesser degree than from other aphids reported on apple and pecan leaves. Accumulation of fresh and dry weights in all tree parts (leaves, lateral shoots, trunk, rootstock, and roots) during the growing season were affected by both spirea aphid and nitrogen fertilization. The spirea aphid reduced accumulation of fresh and dry weights in all tree partitions when trees were harvested at the end of the first growing season. These reductions were still lower than the control when trees were harvested at the ten-leaf stage the following spring. The spirea aphid caused a significant reduction in lateral shoot growth at the end of the growing season and at the ten-leaf stage. Fresh and dry weights of all tree partitions tended to increase with increasing rates of nitrogen. The percentage and the amount of nonstructural carbohydrates (NSC) in all tree partitions were reduced by spirea aphid feeding and were positively related to nitrogen rate. At the ten-leaf stage in the second season, similar results were obtained. Development of spirea aphid and apple aphid was similar on trees fertilized with a moderate rate of nitrogen. Pn and leaf greenness declined to a similar extent with accumulated aphid-days, for both aphid species. Aphid species did not affect any of tree growth or NSC accumulation. / Ph. D.

Population dynamics of selected pests (Panonychus ulmi, Aculus schlechtendali, Aphis citricola, Dysaphis plantaginea spp.) in Virginia apple orchards and predators (Leptothrips mali, Haplothrips subtilissimus, Orius insidiosus, Stethorus punctum, Dereacoris nebulosus, Chrysopa spp.) were monitored during 1977-78 under 3 reduced pesticide programs. The pesticide program with phosalone and Dikarᴿ as its principal components allowed the largest number of predators to remain in the orchard and controlled most pests. L. mali and H. subtilissimus were the most abundant predators and appeared to respond numerically to densities of A. schlechtendali. O. insidiosus and D. nebulosus usually increased late in the season and S. punctum responded to densities of P. ulmi inconsistently but together with thrips may have had an important role in reducing P. ulmi populations. Chrysopa spp. remained at consistently low levels throughout the study. Laboratory studies indicated that phosalone and Dikar were the least toxic to L. mali among the pesticides tested. Benomyl can probably be substituted for Dikar in order to lessen mortality of A. schlechtendali in the field. L. mali was studied in the laboratory to determine aspects of its development, biology and prey relationships. Mean development time (days) for each stage at 23.9°C was: egg, 7.5; Ist larva, 5.7; 2nd larva, 5.4; prepupa, 1.0; pupa I, 1.5; pupa II, 4.0 and total (eggadult), 25.6. The preoviposition period ranged 5-7 days and the mean no. eggs/lab-reared (LR) and field collected (FC) females were: mated - LR, 13.0; FC, 28.0 and unmated - LR, 11.7; FC, 45.1. Mean longevity (days) of unmated females (LR, 50.1 and FC, 54.2, respectively) was greater than that for males and mated females. L. mali completed development on Golden Delicious apple pollen in 23 days (1st stage larva - adult). This thrips fed on the following orchard pests: A. schlechtendali, Tetranychus urticae, Lecanium corni, and on the eggs of Laspeyresia pomonella and Platynota flavedana. No feeding was observed on S. punctum, but L. mali fed on the phytoseiid mite, Proprioseius oudemansi. The functional response of all feeding stages of L. mali to densities of P. ulmi was determined at 18.3, 23.9, and 29.4°C and the numerical response of adult female L. mali to this mite species was investigated. The greatest effect of temperature on the functional response curve was observed with field collected adult female L mali. The numerical response of L. mali reached a maximum of 0.70 eggs/ female/48 h. The individual or joint potential impact of L. mali with S. punctum or O. insidiosus on P. ulmi was evaluated in the laboratory. At a mite density of 45/arena, L. mali with S. punctum killed significantly more P. ulmi than L. mali or S. punctum alone. In 75% of the replicates where L. mali was combined with O. insidiosus, the latter killed and consumed the thrips. A simple, non-destructive, but inefficient visual sampling method for L. mali on apple foliage was compared to a destructive, time-consuming, efficient limb-tapping sampling technique. With this comparison the usefulness of the visual sampling method was improved, thus increasing the potential of this sampling technique. / Ph. D.

Master of Science

The effects of pheromone trap placement on male moth catches of both species were studied. For P. flavedana, traps hung at 2.1 and 3.0 meters captured the greatest number of moths. Trap heights of 1.2, 2.1, and 3.0 meters caught the greatest number of P. idaeusalis moths. The outside-the-canopy trap position captured more P. flavedana moths, while the within-canopy trap location caught the greatest number of P. idaeusalis moths. Traps placed in the west portion of the tree captured the greatest number of P. flavedana moths. P. idaeusalis moth catches were not influenced by compass quadrants. Trap design and pheromone dispenser and rate influenced trap catches of P. flavedana. Development of P. flavedana and P. idaeusalis on a meridic diet was observed at constant temperatures in the laboratory. Lower developmental threshold values for egg, larval, and pupal stages of P. flavedana were: 10.6, 8.6, 9.0°C, respectively. Lower developmental threshold values of 9.7, 7.0, and 8.5°C were estimated for P. idaeusalis egg, larval, and pupal stages, respectively. An average of 101.5 °D_10.6’, 379.6 °D_8.6’, and 126.0 °D_9.0’ were required for development of egg, larval, and pupal stages of P. flavedana, respectively. P. idaeusalis required 104.7 °D_9.7’, 442.7 °D_7.0’, and 132.2 °D_8.5’ to complete development in the egg, larval, and pupal stages, respectively. Differences in rate of development were observed between food sources for both species. Within-tree spatial distribution of egg masses and fruit damage resulting from larval feeding for both species was investigated. P. flavedana egg masses were mostly found in the southern portion of the tree below 1.8 meters. Egg masses of P. idaeusalis were observed in greatest numbers in the southern and eastern quadrants of the tree below 2.8 meters. Fruit damage caused by larvae of both species was greatest in the lower portion of the tree. Wind dispersal of first-instar larvae between trees is believed to have influenced fruit damage distribution. The seasonal activity of P. flavedana and P. idaeusalis was monitored. Degree-day accumulations for first moth catch, first and peak egg deposition, and first and peak egg hatch of both generations are presented. / Ph. D.