Location: Biological Control of Insects Research2013 Annual Report
1a. Objectives (from AD-416):
The long-term objective of this project is to develop improved strains of beneficial insects and baculoviruses through traditional breeding techniques. The specific objectives are to: 1) select and develop beneficial lines of a predator, the spined soldier bug, Podisus maculiventris, for improved bionomic traits such as increased female fecundity, sex ratio, development time, and shelf life, 2) select and develop baculovirus lines for important biopesticide traits such as increased speed of kill, persistence, and broadened host range, and 3) in partnership with small and urban vegetable growers, develop novel beneficial insect and baculovirus delivery systems for application, using such strategies as chemical attractants, artificial diets, and release mechanisms.
1b. Approach (from AD-416):
The goal of this research is to select biological control agents with improved traits for controlling pest insects in greenhouse, organic and small field applications. This project will generate a highly fecund line of the spined solder bug, Podisus maculiventris (and if time permits, a line tolerant to cold storage) and naturally occurring stable, efficacious strains of the celery looper baculovirus, Anagrapha falcifera nucleopolyhedrovirus. We will measure genetic variation within and between the predator populations and the virus populations to assess their potential for selection procedures. Initially we will use egg production traits to direct the selection of predator lines and virulency to direct the selection of virus lines. For the predator lines, genetic variation will be assessed and polymorphisms will be used to identify and confirm associations between genotype and the high fecund phenotype. For the virus strains, genetic variation will be assessed and variable regions will be sequenced to identify genes related to efficacy and stability. Together, this research will produce significant advancements in knowledge of the genomic basis underlying complex traits. It also will build our capability to breed lines of insects and strains of viruses with enhanced production traits and pest control efficacy. We have established collaborations to test the improved lines of predators and viruses at the greenhouse and small plot levels. Two key end products, which we will transfer to industry and producers, will be improved beneficial agents with increased value to commercial insectaries and producers and the technology required to achieve these improved agents.
3. Progress Report:
To accomplish Milestone 1, the genetic variation of the spined soldier bug was compared for field and laboratory colonies from throughout the eastern half of the USA. Selection methods initially used to enhance reproduction in Missouri spined soldier bugs were promising but resulted in excessive in-breeding which ultimately caused the colonies to collapse. Cross-breeding of colonies from different locations has been initiated as another method to increase reproductive capacity in the beneficial predator. For Milestone 2, celery looper baculovirus isolates collected from Missouri previously purified were tested in a laboratory bioassay and found to be similar in strength of infectivity. One representative viral isolate was sequenced. An RNA virus found to co-infect with the celery looper virus was also sequenced. Matching biological function with portions of the viral genomes is currently underway. Additionally, in partnership with Beltsville ARS scientists, the genome of a baculovirus from the cotton leaf worm was sequenced. This virus is closely related to a fall armyworm virus previously sequenced and characterized in this laboratory. Differences in viral infectivity were studied between the armyworm and leaf worm viruses and comparisons between genome sequences were made. These studies will provide information critical to the determination of host range and viral effectiveness which will enable the development of more effective, agriculturally relevant baculoviruses. To accomplish Milestone 3 a leaf bouquet assay, developed in the previous year, was used to quantitate the rate of leaf consumption by differing age and density of the cabbage loopers. These combinations will be used to test for reduced plant damage resulting from applications of a predatory insect or baculovirus.
1. Improving the genetic composition of beneficial insects. Natural genetic diversity in insect populations increases their ability to survive environmental conditions. That diversity can also affect the performance of beneficial insects. ARS researchers in Columbia, Missouri, in collaboration with researchers at the University of Nebraska, Lincoln, Nebraska, compared the genetic variability among field collected spined soldier bugs from Michigan, Mississippi, Missouri, Florida and laboratory reared colonies. Each population was distinct from the others with the Missouri population having the most unique genetic variability. A substantial amount of the genetic variation found in field populations was maintained for multiple generations. These findings support future work to breed and mass produce a strain of high performing spined soldier bugs for use in vegetable insect pest control practices. This work will provide valuable benefits to the environment by reducing chemical insecticide use.
2. Improving the effectiveness of baculoviruses. Baculoviruses are an excellent alternative control for pest moths that can be used in small farm and organic settings. However, they have drawbacks such as slow speed of action and narrow host range. ARS researchers at Columbia, Missouri studied the genome sequence of very closely related baculoviruses that had differing host ranges and infectivity. Comparison of the genetic sequences has identified genes that are potentially responsible for altering the host range and effectiveness of the baculoviruses.
3. Improving the performance of predatory insects. Genetics and nutrition are two of the most influential factors impacting insect reproduction. ARS researchers at Columbia, Missouri are developing genetic markers that can be used to select highly reproductive beneficial insects and develop diets that will support their nutritional needs. Comparison of the development of beneficial insect predators grown on varying dietary treatments indicated several genes and nutrient concentrations associated with high reproductive capacity in beneficial insect predators. These findings will be used to produce insect predators with improved performance traits for mass production and field applications. The improved traits will lower the costs of mass rearing beneficial insect predators, which will increase used of biological control programs to reduce the insecticide load in the environment.
Breitenbach, J.E., El-Sheikh, E.A., Harrison, R.L., Rowley, D.L., Sparks, M., Gundersen, D.E., Popham, H.J. 2013. Determination and analysis of the genome sequence of Spodoptera littoralis multiple nucleopolyhedrovirus. Virus Research. 171(1):194-208.