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Project description

Integration of tactics for management of invasive insect pests: adaptations for an expanding community of pests and natural enemies in the urban forest. (01XU032)
Program Exotic Pests and Diseases Research Program
Principal
investigators
T.D. Paine, Entomology, UC Riverside
J.G. Millar, Entomology, UC Riverside
Host/habitat Eucalyptus
Pest Eucalyptus Longhorned Borers Phoracantha semipunctata and P. recurva; Eucalyptus Tortoise Beetle Trachymela sloanei; Redgum Lerp Psyllid Glycaspis brimblecombei
Discipline Entomology
Review
panel
Urban Systems
Start year (duration)  2001 (Three Years)
Objectives Determine if cultural practices of high levels of irrigation and nitrogen fertilization implemented to improve resistance of eucalyptus trees to borers result in increased suitability and susceptibility of foliage to leaf beetles and psyllids.

Test whether soil-injected systemic insecticides applied to protect trees against redgum lerp psyllid, tortoise beetle, and borers have negative impact on their natural enemies.

Determine if there is an interaction between water and fertilization treatments, systemic insecticide efficacy, and impact on natural enemies.

Third-year
progress
Under plantation conditions characterized by uniform irrigation, uniform tree age, and uniform tree spacing, treatment of Eucalyptus rudis trees by soil injection of imidacloprid continued to be highly significant for reducing redgum lerp populations. Previous studies have demonstrated that bark moisture content of Eucalyptus trees is critical resistance to colonization by the eucalyptus longhorned borer. If bark moisture is maintained above approximately 55%, the young beetle larvae are incapable of penetrating through the bark tissue. Thus, irrigation of trees to maintain critical levels of bark moisture has been an important cultural management tool. However, moisture and fertilization could make the trees more susceptible to the psyllids. Similar to what was observed in the first year, results in the second year demonstrate that trees under low irrigation treatments had significantly higher densities of psyllids than trees maintained under high levels of irrigation. Trees with high levels of nitrogen fertilization had significantly higher densities of psyllids than trees maintained under low levels of fertilization. Not surprisingly, analysis of the combination of treatments demonstrated that trees maintained under conditions of high irrigation and low fertilization were least colonized by psyllids.

Parasitoids of the herbivores on eucalyptus may be exposed to systemic insecticides if the pesticide is present in floral nectar and if the parasitoids feed in the flowers. We have demonstrated that the egg parasitoid Avetianella longoi and Syngaster lepidus will feed on sugar solution containing imidacloprid and established the LC50 levels for the parasitoids to the insecticide.

Second-year
progress
Under plantation conditions characterized by uniform irrigation, uniform tree age, and uniform tree spacing, treatment of Eucalyptus rudis trees by soil injection of imidacloprid was highly significant for reducing red gum lerp populations. Previous studies have demonstrated that bark moisture content of Eucalyptus trees is critical resistance to colonization by the eucalyptus longhorned borer. If bark moisture is maintained above approximately 55%, then the young beetle larvae are incapable of penetrating through the bark tissue. Thus, irrigation of trees to maintain critical levels of bark moisture has been an important cultural management too. However, moisture and fertilization could make the trees more susceptible to the psyllids. Our results demonstrate that trees under low irrigation treatments had significantly higher densities of psyllids than trees maintained under high levels of irrigation. Trees with high levels of nitrogen fertilization had significantly higher densities of psyllids than trees maintained under low levels of fertilization. Not surprisingly, analysis of the combination of treatments demonstrated that trees maintained under conditions of high irrigation and low fertilization were least colonized by psyllids.

Parasitoids of the herbivores on eucalyptus may be exposed to systemic insecticides if the pesticide is present in floral nectar and if the parasitoids feed in the flowers. We have demonstrated that the egg parasitoid Avetianella longoi will feed on sugar solution containing imidacloprid and established the LC50 for the parasitoid to the insecticide. The flowers are just beginning to bloom and we are in the process of collecting nectar for pesticide residue analysis and to determine if the nectar is attractive to the wasps. The same procedures will be followed for two other parasitoids.

First-year
progress
The project is a three-year effort and we are less than six months into the first year. We are on schedule for completion of the proposed research. During the first six months, we have all of the experimental nitrogen and irrigation treatments in place and we have increased the number of red gum trees in the experimental plots. Tensiometers have been established in the plots to monitor soil-moisture levels. The insecticide treatments will be initiated within two weeks. We have also arranged to plant an additional 150 trees of E. maculata to include the newly introduced spotted gum lerp psyllid in the investigation. We have also begun the establishment process for the parasitoid of the redgum lerp psyllid so that we have populations of that insect with which to work in 2002.

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