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.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/40272 |
| Date | 30 October 2008 |
| Creators | Parrella, Michael P. |
| Contributors | Entomology |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | ix, 138 pages, 3 unnumbered leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 06473759, LD5655.V856_1980.P377.pdf |
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