2010 Annual Report 1a.Objectives (from AD-416) 1) Determine basic parameters of whitefly transmission of Squash vein yellowing virus (SqVYV);. 2)Characterize how mixed infections of SqVYV with the aphid-transmitted Papaya ringspot virus type-W (PRSV) and/or the whitefly-transmitted Cucurbit leaf crumple virus affect transmission of SqVYV;. 3)Determine the effects of insecticides (including oils) on transmission of SqVYV; and. 4)Describe the spatial distribution of immature whiteflies on watermelon. 1b.Approach (from AD-416) Greenhouse experiments will be run to determine basic parameters of whitefly transmission of SqVYV. Experiments will determine the mode of transmission (persistent, semi-persistent or non-persistent) of SqVYV by whiteflies. These experiments will show how efficiently whiteflies transmit SqVYV, how long they must feed to acquire/transmit SqVYV, and how long whiteflies retain SqVYV. For the mixed-infection work, SqVYV-infected squash source plants that are additionally infected with PRSV-W and/or CuLCrV. Mixed infections will be created by insect inoculation of each virus separately, either on the same day or one week apart. Greenhouse experiments will also be run to assess the effects of pymetrozine, repellants such as neem, and oils on acquisition and transmission of SqVYV. Specifically, it will be determined if the insecticide (including oil and neem-based product) kills the whitefly or otherwise interfere with transmission before the whitefly transmits SqVYV to uninfected plant and/or whether it blocks the whitefly’s ability to acquire SqVYV from an infected plant? Finally, field experiments (two seasons for two years) will be conducted to describe the spatial distribution of immature whiteflies and whitefly eggs. Each week during the growing season, plants will be randomly sampled and the number of eggs and nymphs will be counted on a sample of leafs, with the position and age of each being recorded. Appropriate analysis will follow. 3.Progress Report This research relates to inhouse objective 1: Characterize ecology, biology, epidemiology, genetics and host interactions of domestic, exotic, newly emergent and re-emerging pathogens. The intent of this study is to develop basic insect vector acquisition and transmission parameters for Squash vein yellowing virus (SqVYV), alone or in commonly observed mixed infections with Cucurbit leaf crumple virus (CuLCrV), Papaya ringspot virus (PRSV-W) and/or Cucurbit yellow stunting disorder virus (CYSDV). This information will be a key component of management strategies we develop as our preliminary data indicates that SqVYV is not efficiently transmitted by whiteflies and is not retained for more than a day. SqVYV may require fairly high whitefly populations to spread rapidly. Results to date continue to be consistent with a semi-persistent mode of transmission for SqVYV. In addition, within plant distribution of adult and immature whiteflies on watermelon is being characterized to enable the development of more accurate sampling methods. We studied the effect of mixed infections of PRSV-W and SqVYV on whitefly transmission of SqVYV to watermelon and squash plants. Results suggest that transmission of SqVYV from a plant that is also infected with PRSV-W is not affected when infection by SqVYV occurs before PRSV infection. However, when infection by PRSV-W occurs before SqVYV or simultaneously, transmission of SqVYV is reduced. We earlier found that if both viruses were introduced at the same time, transmission of PRSV-W from the infected plants by aphids was greatly reduced. Studies still remain to be conducted to look at the effect of mixed viral infections between Cucurbit leaf crumple virus (CuLCrV) and/or Cucurbit yellow stunting disorder virus (CYSDV) and SqVYV. For additional details see the report under the parent project 6618-220000-034-14R. Monitoring was provided by phone calls, emails and site visits.