2008 Annual Report
1a.Objectives (from AD-416)
Specific objectives are to a) Identify and characterize host plant resistance to sweetpotato whitefly in melons and to the soil insect complex in sweetpotato, and facilitate incorporation of resistance factors into advanced breeding lines and new vegetable cultivars; b) assess the importance of biological control agents of sweetpotato whitefly and of insect pests of sweetpotato and cucurbits, and develop techniques for their conservation and utilization as management tools in vegetable production systems; and c) develop cost effective, biologically-based technologies for use in integrated pest management (IPM) programs for sweetpotato, cucurbits, and other vegetable crops.
1b.Approach (from AD-416)
Identify sources of resistance and determine heritability of resistance against sweetpotato whiteflies in melon and watermelon, and against soil insect pests of sweetpotatoes; facilitate incorporation of resistance into advanced sweetpotato breeding lines and new cultivars; determine chemical and physical mechanisms of resistance in sweetpotato to soil insect pests; investigate the influence of leguminous host plants on parasitoids of whiteflies; survey predators in South Carolina for biological control agents for whiteflies; determine overwintering ability of whitefly predator Delphastus catalinae; establish food preferences of predator Engytatus modestus; assess the use of baculoviruses for control of pickleworms, melonworms, and soil pests of sweetpotatoes; develop trapping methods for pickleworm moths, melonworm moths, sweetpotato weevils, Diabrotica spp., and whiteflies using pheromones and kairomones; evaluate alternative cropping systems for sweetpotatoes and other vegetables; and evaluate LED-modified traps for whitefly control.
Fourteen insect viruses were evaluated for control of pickleworm larvae. The most effective were Baculoviridae isolated from velvetbean caterpillar (AgMNPV) and alfalfa looper. Five stilbene fluorescent brighteners significantly increased efficacy of AgMNPV against pickleworm larvae. As part of the on-going sweetpotato breeding program at the US Vegetable Laboratory (USVL), over 250 sweetpotato clones were grown in replicated field plots, harvested in October 2007, and evaluated for yield, quality factors, and resistance to soil insect pests. Included were first-year seedlings, second-year seedlings, intermediate clones, and advanced clones. A similar number of sweetpotato breeding lines have been planted in 2008 and these plots will be harvested in October. Over 2,500 sweetpotato seeds were collected from a polycross breeding nursery of 25 parental lines that was established in 2007. These seeds were planted in a greenhouse and challenged with root knot nematodes. Greenhouse seedlings were evaluated for nematode resistance and root characteristics (color and shape), with approximately 65% of the seedlings being discarded because they did not meet quality standards. The remaining seedlings were transferred to 5-plant field plots for further evaluation. In cooperation with a Research Agronomist, several sweetpotato genotypes were evaluated for susceptibility to damage from the herbicide, clomazone. There was a wide range of response to this herbicide among the genotypes. In cooperation with a research plant pathologist, several sweetpotato genotypes that had been taken through meristem culture to remove sweetpotato leaf curl virus were evaluated in field plots against the same genotypes that still contained leaf curl. For most gentoypes, there was a significant yield increase after leaf curl virus was eliminated. Experiments on the B-biotype sweetpotato whitefly (also call silverleaf whitefly) were conducted on newly identified wild and cultivated host plants of this species. Cucurbit PIs were screened for their resistance to the sweetpotato whitefly. Field and laboratory data were collected on predation of the sweetpotato whitefly by the big-eyed bug (Geocoris punctipes) and the minute pirate bug (Orius insidiosus) based on DNA analyses and direct observations. Experiments were conducted on transmission of the sweet potato leaf curl virus by the B-biotype sweetpotato whitefly. Field and greenhouse studies were conducted on the use of reflective mulch and resistant plants for management of the B-biotype sweetpotato whitefly in watermelon. This project contributes to National Program 304, Crop Protection and Quarantine (100%). The project specifically addresses Problem A (Traditional Biological Control), Problem B (Breeding for Host Plant Resistance), Problem C (Physical/Mechanical and Cultural Control), and Problem D (Other Biologically-Based Control) in Component V, Pest Control Technologies; and Problem A (Sampling Methods, Detection, and Monitoring) and Problem C (Development of IPM Systems) in Component VI, Integrated Pest Management and Areawide Suppression of National Program 304 Crop Protection & Quarantine.
Quantification of Virus Transmission by Sweetpotato Whitefly.
The sweetpotato whitefly transmits many viruses to crops including the Sweet Potato Leaf Curl Virus (SPLCV). Based on symptoms and DNA analyses, transmission of the virus by the B-biotype sweetpotato whitefly was determined. Both males and females of the whitefly vector the virus and their ability to obtain and transmit the virus increases with an increase in time, and the insect continued to transmit the virus for as long as 30 days after it fed on an infected plant. The results help in the epidemiology of the SPLCV in sweetpotato and have direct implications to the numerous viruses that are spread to and among crops by this pest. The research contributes to National Program 304 Crop Protection and Quarantine, specifically, component VI (Integrated Pest Management Systems and Areawide Suppression), Problem A (Sampling Methods, Detection and Monitoring).
Identification of New Host Plants for Sweetpotato Whitefly.
The sweetpotato whitefly is a widespread insect pest. It feeds on many types of plants and it transmits plant viruses to crops. A total of 49 new host plants were identified for this pest. The new hosts include weeds and other wild plants and three cultivated crops (oats, proso millet, and winter wheat). The results indicate that these three crops are poor hosts for this whitefly as compared with good host plants such as cucurbit crops. The research contributes to National Program 304 Crop Protection and Quarantine, specifically, component VI (Integrated Pest Management Systems and Areawide Suppression), Problem A (Sampling Methods, Detection and Monitoring).
5.Significant Activities that Support Special Target Populations
|Number of New Germplasm Releases||1|
|Number of Non-Peer Reviewed Presentations and Proceedings||8|
Hoelmer, K.A., Simmons, A.M. 2008. Yellow Sticky Trap Catches of Parasitoids of Bemisia tabaci (Hemiptera: Aleyrodidae) in Vegetable Crops and Their Relationship to In-field Populations. Environmental Entomology. 37:391-399.
Jackson, D.M., Bohac, J. 2007. Evaluation of Pheromone Traps for Monitoring Sweetpotato Weevils. Journal of Agricultural and Urban Entomology. 23(3): 141-158.
Legaspi, J.C., Legaspi,Jr, B.C., Simmons, A.M. 2008. Life table analysis for immatures and female adults of the predatory beetle,Delphastus catalinae,feeding on whiteflies under three constant temperatures. Journal of Insect Science. 8(7). Available online:insectscience.org.
Legaspi, J.C., Simmons, A.M., Legaspi,Jr, B.C. 2006. Prey preference by Delphastus catalinae (Coleoptera: Coccinellidae) on Bemisia argentifolii (Homoptera: Aleyrodidae): effects of host plant and prey stages.. Florida Entomologist. 89(2).
Simmons, A.M., Legaspi, J.C., Legaspi, B. C. 2008. Responses of Delphastus catalinae (Coleoptera: Coccinellidae), a Predator of Whiteflies (Hemiptera: Aleyrodidae), to Relative Humidity: Oviposition, Hatch and Immature Survival. Annals of the Entomological Society of America. 101:378-383.