ix, 152 leaves : photos, graphs, tables, map. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Entomology, 1980

To make use of the information on infestation estimates of forage insect pests obtained by the conventional methods of sampling, it is important to estimate the actual losses taking place in association with definite numbers of the insect. Six month old red clover, alfalfa, and birdsfoot trefoil plants were exposed for a month to spittlebug infestations of 0, 50, 100, and 150 adults. Although the spittlebug mortality was lowest when reared on alfalfa and highest on birdsfoot trefoil, yellowing appeared on alfalfa and birdsfoot trefoil. On red clover there was a consistent increase in protein and nitrogen free extract and a reduction in crude fiber and ash content indicating slight reduction in growth. None of these differences were significant. On alfalfa the loss of xylem sap due to feeding caused a consistent general reduction of proteins, fat and ash content and an increase in dry matter and nitrogen free extract. Of these constituents only the increase in dry matter was significant with an infestation of 150 spittlebugs per cage. No differences in dry matter, proteins and fat were significant. Another test on 4 month old alfalfa with infestation levels of 0, 100, 200 and 300 showed similar consistent patterns but the difference in dry matter was significant only when the infestation was 200 spittlebugs or more. On birdsfoot trefoil there was a consistent increase of dry matter, proteins, and ash and reduction of fat and crude fiber. Only the difference of dry matter and fats was consistent showing that an infestation of 100 or more spittlebugs per sq ft will affect the general growth of the plants. The survival of 1st instar nymphs of the pea aphid (a phloem feeder) was very poor on birdsfoot trefoil. There was a fair amount of survival on red clover and those on alfalfa survived fully. There was no visible symptoms on birdsfoot trefoil and red clover but the alfalfa showed retarded growth. On red clover there was a consistent increase of dry matter, fat, crude fiber and nitrogen free extract but a reduction of proteins. The difference in crude fiber was significant when the infestation was 1000 pea aphid nymphs or more. A consistent reduction of proteins and crude fiber was also recorded on alfalfa but these differences were not significant. On birdsfoot trefoil, there was a decrease in dry matter and an increase in fat and ash content. The difference in ash content was significant when the infestation of pea aphid nymphs was 1000 or more. Potato leafhopper (phloem feeder) injury was very characteristic on birdsfoot trefoil. The terminal 1 to 2 inches of the sterns became wilted and bent down. On alfalfa there was gradual yellowing and the retarded growth was evident. The red clover did not show any characteristic symptoms. Infestations of 20 or more caused a consistent increase in protein, fat, crude fiber and a reduction of nitrogen free extract. On alfalfa there was consistent decrease in dry matter. On birdsfoot trefoil, there was consistent increase in dry matter, fat, and nitrogen free extract but a reduction of crude fiber showing that feeding on birdsfoot trefoil probably retards growth and condensation of carbohydrates to form crude fibers. The increase in fat was significant when the infestation was 40 potato leafhoppers or more. Alfalfa weevil adult feeding caused characteristic stripping of leaves, girdling of stem and drying of the entire plant. Feeding of 10 or more weevils for 18 days on a two month growth of alfalfa after the 1st cutting, cause a consistent reduction of proteins, fat and crude fiber and an increase of dry matter, ash, and nitrogen free extract. Increase of percent dry matter was significant when the infestation of alfalfa weevil adults was 20 or more. In another test, the dry matter, fat and ash gave similar consistent results, when 40, 60, and 80 adults were fed on 4 month old alfalfa for 18 days. Reduction of percent fat was significant when the infestation was 40 or more alfalfa weevil adults. Alfalfa weevil larval feeding showed stripping of the leaves and buds. Infestation of 30 or less, 2nd to 4th instar larvae for 12 days caused a consistent reduction of fat and ash and an increase of dry matter, proteins and crude fiber. The infestation was not high enough to show a significant change in plant constituents. / Ph. D.

Selected insecticides were evaluated to determine effects on the potato leafhopper and its predators. Three types of tests were conducted. First, the common predators of the potato leafhopper in alfalfa were examined to determine their response to the stages of the leafhopper. Second, under field conditions, insecticides were tested to detect effects on the populations of the insects. Finally, LC₅₀ toxicities of selected insecticides were investigated under laboratory conditions. In the predation tests, two studies were conducted, namely, predation on egg stage and predation on nymphal and adult stages of the potato leafhopper. An indirect method of determining egg predation was employed because potato leafhopper eggs are not visible, being concealed in the xylem and phloem tissues. Using two sets of treatments (with and without predators), the potato leafhopper females were allowed to oviposit in predation cages and the suspected predators introduced thereafter. Hatching nymphs were counted and used as indications of the number of eggs laid. Nabis americoferus and Orius insidiosis were found to be predaceous on eggs of the potato leafhopper. In the predation tests, using nymphal and adult stages of the potato leafhopper, the following adult and larval stages of insects were confirmed as predators: Hippodamia convergens, Coccinella novemnotata, and Chrysopa carnea. Two field tests, one in summer of 1977 and one in summer of 1978, were conducted to determine the influence of insecticides on populations of potato leafhoppers and its predators in alfalfa. Samples were taken using a 38 cm sweep net employing a 180° motion at 2 days, 1 week, and 2 weeks after treatment. In both tests, significant control was provided by the chemicals against potato leafhoppers 48 hours following application. A gradual population recovery occurred one week and two weeks after treatment. Most of the entomophagous insects sampled were adversely affected by insecticides. No statistical differences in yield and percent dry matter were obtained with various insecticidal treatments. The acute toxicities of selected insecticides on potato leafhopper, tarnished plant bug, and damsel bug were investigated. The bioassay method used was the immersion technique and toxicity was expressed in LC₅₀. The relative toxicities of Nabis americoferus to 50° Empoasca fabae and Lygus lineolaris were obtained by deriving the selectivity ratios. Selectivity ratios are calculated by dividing the LC₅₀ of the non-target organism divided by the LC₅₀ of the pest. The ratios indicated that most of the insecticides tested were highly selective. Among the organophosphates, azinphosmethyl was the most selective, while among the carbamates, carbaryl was the most selective. / Master of Science

Bibliography: leaves 196-210 / xi, 256, [85] leaves : (ill. (some col.) ; 31 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Entomology, Waite Agricultural Research Institute, 1985

Virginia is a natural laboratory for studying overwintering habits of the alfalfa weevi1. At higher elevations, winters are relatively harsh and weevil pressure on the alfalfa crop is usually light. Much heavier pressure is the rule at lower elevations where winters are milder. The goal of this study was to examine the effects of fall and winter temperatures, parasites, and fall regrowth management on population dynamics of overwintering stages of this insect. Sixteen commercial alfalfa fields in Montgomery Co. (elevation 610 m) and Bedford Co. (elevation 300 m) were used in the study. Approximately half the fields each year were either harvested or grazed to remove fall regrowth. In the other fields, fall regrowth was left standing through the winter. Six different pitfall trap designs were compared for collection efficiency, installation and servicing effort, and cost. Barrier traps outperformed the other trap designs and were inexpensive and easy to install and service. Sweepnet samples were used to monitor weevil adults during their fall migration. A newly designed sampling device which removes all plant material, litter, and approximately 2 cm of soil from a 1/20 m² area, was used to measure absolute densities during fall and winter. Based on these absolute density samples fewer adults overwintered within fields in which fall regrowth was removed. Dissections revealed the presence of three parasites: Hyalomyodes trianqulifer (Loew), Microctonus aetheopoides Loan, and M. colesi Drea. Total parasitization rates were low. The highest measured rate was 16.1% in Bedford Co. in 1984-85. Female reproductive development also was determined through dissection. Females reach sexual maturity shortly after returning to alfalfa fields in the fall. Most contain full-size eggs in their oviducts from late fall through the winter. Egg densities as measured by laboratory incubation of field collected plant material indicated no differences related to elevation in early February, but significantly more viable eggs were present by late March at the low elevation site. In 1984, Bedford Co. samples indicated significantly more eggs in fields receiving no fall regrowth management. A simulation model called OAWSIM (Overwintering Alfalfa Weevil Simulation) was developed to examine the influence of factors which affect overwintering life stages. Model predictions indicate fall and winter temperatures, and fall regrowth management are major influences on the population dynamics of this insect. / Ph. D.

Three sampling methods for estimating abundance of alfalfa weevil (AW) larvae (Hypera postica Gyllenhal) were evaluated for both accuracy and precision. Calibration equations were developed to convert intensity estimates of AW larvae among sampling methods. Greenhouse experiments evaluating the interaction of moisture stress and defoliation by AW larvae indicated that yield response of alfalfa to AW feeding is dependent on moisture stress levels. Field studies on the influence of AW feeding on alfalfa confirmed the importance of moisture stress in alfalfa tolerance to weevil feeding. Quadratic regression models are presented to predict yield loss and changes in stem density as a function of weevil intensity. A sequential sampling plan was developed and validated for use in pest management decision making. Validation of the plan indicated an average error rate of 1.8%, with the number of samples needed reduced by 55% in 1980, 53% in 1981, and 28% in 1982. A net benefit analysis the Virginia Alfalfa IPM program indicated that growers participating in the program during 1981-84 realized an estimated average increase in net revenue of $8.80 per hectare from the alfalfa weevil scouting program, and $28.13 per hectare from the potato leafhopper scouting program. / Ph. D. / incomplete_metadata