The behaviour of the orchard mites Bryobia pretiosa (Koch) and Metatetranychus ulmi (Koch) and four species of predators was investigated both on unsprayed and on sprayed apple trees. On unsprayed trees the host mites were found to be most abundant on the east sides; no consistent directional preference was found for the predacious species. Small apple leaves supported the same number of M. ulmi per unit area as large leaves, but more mites of the genus Tetranychus. On unsprayed trees a negative correlation between the total number of predators and the number of host mites was recorded. In abandoned orchards the predators were capable of controlling the host mites and maintaining them at a level below that of economic significance. Each of the insecticides DDT, Parathion, and lead arsenate, was found to be very toxic to all species of predators recorded, and thus hindered or entirely prevented natural control of the host mites. In every instance lead arsenate and DDT produced an increase in the population of B. pretiosa, this effect being partially chemical and partially due to a lack of predators on the sprayed trees. Lead arsenate caused an increase in the population of M. ulmi whereas DDT reduced it to a slight extent. Under arid conditions Parathion caused an increase in the population of B.pretiosa; under less arid conditions the mite was eliminated. Parathion had no effect on M. ulmi in a commercial orchard while, in the same orchard, it caused a great increase in Tetranychus spp. The latter species were reduced by DDT in the commercial orchard. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

No description available.

No description available.

This work was done to determine the toxicity and bioactivity of four organic insecticides and ultimately find answers about their toxic potential. Thus, farmers will be able to take the necessary precautions when using them. This investigation was performed in the Laboratory of Biology of the Eastern University Center (Chiquimula) at the University of San Carlos, Guatemala. In order to determine the acute toxicity and bioactivity of the organic insecticides ANONAZO, BOX, AJORIN, and NARCISO, five doses were used in albino mice and three concentrations in nauplii of brine shrimp (Artemia salina). The finney basic program was used for calculating the average lethal dose (DL50) and the average lethal concentration (CL50). The results showed that in albino mice, ANONAZO had a DL50=707.10 mg/kg of weight which is classified as slightly toxic according to the Williams table. However, a tendency towards being moderately toxic was also present. CAJA had a DL50=>5000 mg/kg of weight classifying it as practically non-toxic. AJORIN had a DL50=4530 mg/kg of weight corresponding to the slightly toxic classification. In addition, a tendency towards being practically non-toxic was present. NARCISO had a DL50=158.11 mg/kg of weight corresponding to the moderately toxic classification but on the border of highly toxic. In regards to bioactivity in nauplii of brine shrimp: Anonazo, Ajorin, and Narciso had values less than 1000 ppm, which indicates that they have bioactivity. Caja showed no bioactivity.

No description available.

No description available.

The brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), is a major pest of vegetable crops, fruit crops, and even ornamental plants in the Mid-Atlantic States. Organic growers have limited chemical options to manage this pest, and are in need of better management options. Several organically-approved insecticides including pyrethrins (Pyganic), azadirachtin (Aza-Direct), azadirachtin + pyrethrins (Azera), spinosad (Entrust), potassium salts of fatty acids (M-Pede), sabadilla alkaloids (Veratran D), extract from Burkholderia sp. (Venerate), and one experimental product, potassium salts + spinosad (Neudorff 1138), were evaluated for toxicity to BMSB nymphs and adults using lab bioassays and field trials on tomatoes and peppers. Another potential control option is to use natural chemicals to deter BMSB feeding in vegetables. Kaolinite [Al4Si4O10 (OH)8] (Surround WP); a white, plate-shaped, aluminosilicate mineral that is sprayed on plants to alter the appearance, feel, and smell of a plant to an insect. Essential oils (Ecotec) are chemicals produced by plants which are repellent and even toxic to certain insects, and by mimicking octopomine these chemicals disrupt the insect's neurotransmitters. Treatments were evaluated in choice test bioassays and field experiments on peppers using weekly applications of the highest labeled rates of the products. The results showed that, although some organically-approved insecticides demonstrate a high level of activity on BMSB in lab bioassays, none of these products appear to be effective at reducing stink bug damage to fruiting vegetables in the field. However, kaolinite provided significant control of BMSB nymphs (p=0.03) and adults (p=0.01) in both choice test bioassays and in field trials. Essential oils did not provide any significant control of BMSB in choice test bioassays or in field trials. Further research is needed to determine if the efficacy of kaolinite holds up under heavy pest pressure. / Master of Science in Life Sciences

The Quotient Method (QM), a laboratory-based risk assessment methodology used by the Environmental Protection Agency to evaluate pesticides for registration and use, has not been thoroughly field-tested and its performance has not always been reliable. My objective was to determine if variation in vegetation structure or diet of exposed animals could result in adverse ecological effects that were not predicted by the QM. In April and early May 1993, I established populations of herbivorous gray-tailed voles (Microtus canicaudus) and omnivorous deer mice (Peromyscus maniculatus) in 24 0.2-ha enclosures planted with alfalfa (Medicago sativa). Alfalfa in 12 enclosures was mowed on 22 June to reduce vegetation height. Small mammal populations were monitored by live trapping from May through August 1993. On 14 July, an organophosphorus insecticide, azinphos-methyl, was applied at 0, 0.88, and 3.61 kg/ha. Insecticide residues were measured on canopy-level spray cards, soil samples, and alfalfa. I compared the observed residue concentrations with predictions based on the nomogram used to estimate exposure for QM risk assessments. I also compared QM predictions of risk with observed effects on population size and growth, survival, reproductive activity, recruitment, body growth, movements, and diet of the small mammals. Much of the insecticide reached ground level in mowed enclosures, but dense alfalfa intercepted most of the spray in unmowed enclosures. The mean half-life of azinphos-methyl on alfalfa was 3.4 days and was not affected by mowing. Mean residue concentrations on mowed alfalfa and the top 15 cm of unmowed alfalfa were underestimated by the QM exposure nomogram. Therefore, pesticides may pose greater risk to organisms inhabiting sparse vegetation or the tops of plants than predicted by the QM. Treatment with azinphos-methyl at 3.61 kg/ha caused severe effects in both mowed and unmowed enclosures on population size and growth, survival, recruitment, and body growth of voles. Effects of azinphos-methyl on vole recruitment and body growth and on survival of female voles were greater in mowed than in unmowed enclosures. However, I did not find that population-level responses of voles to the chemical differed between mowing treatments. Most effects on voles were of short duration (<27 days) but vole densities in 3.61 kg/ha enclosures remained depressed >6 weeks after spraying. The 3.61 kg/ha application rate resulted in a 42% decrease in deer mouse densities in mowed enclosures during the week of spraying, but the insecticide had no adverse effects on deer mice in unmowed enclosures. In addition, the insecticide may have reduced recruitment of deer mice in mowed enclosures. Analysis of deer mouse feces indicated that consumption of arthropods increased in insecticide-treated enclosures just after spraying occurred. Survival, reproductive activity, body growth, and movements of deer mice were highly variable and not significantly affected by azinphos-methyl. Mowing resulted in greater residue concentrations than predicted and, consequently, the insecticide adversely affected voles and deer mice in mowed enclosures at application rates characterized as low risk by the QM. However, food aversion or selective feeding on alfalfa tops may have resulted in similar exposure of voles to the 3.61 kg/ha treatment in mowed and unmowed enclosures. I did not find that insectivorous feeding behavior of deer mice made them more susceptible than predicted. Although residue concentrations on alfalfa did not follow predictions, the gross pattern of effects on small mammals was consistent with QM risk characterization. However, the QM may underestimate exposure and risk when pesticides are sprayed on sparse vegetation. / Graduation date: 1995

Graduation date: 2002