Influence of seasonal nitrogen nutrition fluctuations in orange and lemon trees on population dynamics of the glassy-winged sharpshooter (Homalodisca coagulata).

The glassy-winged sharpshooter (GWSS) is a xylem feeder that develops conspicuous, year-round populations in many citrus-producing regions of California. Field studies were conducted in a combined lemon and orange orchard to determine the influence of changing amino acid concentrations on relative densities of GWSS. Nineteen protein amino acids were detected in xylem fluid of both lemon and orange trees. Although annual profiles of total and essential amino acids were similar for each citrus species, mean concentrations were consistently higher in lemons than in oranges for most of the year, except for one critical period in late winter-early spring when concentrations were higher in oranges. Principal component analysis followed by factor analysis was performed individually on lemon and orange data sets to identify a reduced number of orthogonal factors composed of amino acids having similar seasonal profiles. Four factors were identified for each citrus species that accounted for 85% and 79% of the total variation in the orange and lemon analyses, respectively. These were then examined with respect to shifts in GWSS numbers that occurred asynchronously in lemons and oranges over the annual population cycle. Three distinctive number shifts were identified that included a peak in adult numbers in lemons during August 2001, significantly higher numbers in lemons relative to oranges during midwinter, and finally an increase in oranges of both adults and nymphs during spring 2002. Various groups of amino acids, i.e., factors, displayed peak annual or elevated levels during the intervals when shifts in GWSS numbers were occurring. Soluble protein levels in oranges and lemons did not correspond to shifting GWSS numbers as certain amino acids. However, soluble protein levels were higher in oranges during late winter/early spring when GWSS adults were sexually active. Potential roles of these amino acids and proteins in GWSS host selection are discussed.

Sweet potato (Ipomoea batatas) trypsin inhibitors expressed in transgenic tobacco plants confer resistance against Spodoptera litura.

A sweet potato (Ipomoea batatas cv. Tainong 57) trypsin inhibitor gene was introduced into tobacco plants (Nicotiana tabaccum cv. W38) by Agrobacterium tumefaciens- mediated transformation. From 30 independent transformants, three lines with high level of expression were further analyzed. The trypsin inhibitor gene, under control of the 35S CaMV promoter, led to the production of the trypsin inhibitor proteins up to 0.2% of the total protein. In insecticidal bioassays of transgenic tobacco plants, larval, growth of Spodoptera litura (F.), the tobacco cutworm, was severely retarded as compared to their growth on control plants. This observation implied that expression of sweet potato trypsin inhibitor can provide an efficient method for crop protection.

Determination and Distribution of cry-Type Genes of Bacillus thuringiensis Isolates from Taiwan.

Using PCR with a set of specific oligonucleotide primers to detect cryI-type genes, we were able to screen the cry-type genes of 225 Bacillus thuringiensis soil isolates from Taiwan without much cost in time or labor. Some combinations of cry genes (the cry-type profile) in a single isolate were unique. We identified five distinct profiles of crystal genes from the B. thuringiensis soil isolates from Taiwan. The cry genes included cryIA(a), cryIA(b), cryIA(c), cryIC, cryID, and cryIV. Interestingly, 501 B. thuringiensis isolates (93.5% of the total number that we identified) were isolated from areas at high altitudes. The profiles of cry-type genes were distinct in all isolation areas. The distribution of cry-type genes of our isolates therefore depended on geography. Using PCR footprinting to detect cryIC-type genes, we identified two distinct cryIC footprints from some of our isolates, indicating that these isolates may contain novel cryIC-type genes. B. thuringiensis isolates containing cryIA(a)-, cryIA(b)-, and cryIA(c)-type genes exhibited much greater activity against Plutella xylostella than did other isolates, indicating that multiple cry-type genes may be used as markers for the prediction of insecticidal activities.