Russell Nagata

Role of Leaf Sheath Lignification and Anatomy in Resistance Against Southern Chinch Bug (Hemiptera: Blissidae) in St. Augustinegrass

ABSTRACT Southern chinch bug, Blissus insularis Barber (Hemiptera: Blissidae), is the most serious insect pest of St. Augustinegrass Stenotaphrum secundatum (Walter) Kuntze, a common lawngrass grown in southeastern U.S. states. Host plant resistance to southern chinch bug has been identified in the polyploid St. Augustinegrass‘FX-10′ and the diploid ‘Captiva’. The objective of this research was to identify possible physical mechanism(s) explaining chinch bug resistance in these cultivars. We studied the distribution of chinch bug salivary sheaths in the preferred tissue for feeding (the axillary shoot) of the two resistant cultivars and two susceptible cultivars, paired for ploidy (‘Floratam’, polyploid, and Palmetto, diploid). We also investigated the potential role of axillary shoot lignification and anatomy in chinch bug resistance. Salivary sheaths were more abundant on the outermost leaf sheath of axillary shoots of resistant cultivars compared with susceptible cultivars. In contrast, fewer salivary sheaths reached the innermost meristematic tissue in the axillary shoots of resistant St. Augustinegrass cultivars than in the two susceptible cultivars. The polyploid cultivars FX-10 and Floratam had higher total lignin in axillary shoots compared with the diploid cultivars Captiva and Palmetto. However, total lignin content was not correlated with resistance to southern chinch bug. Light microscopic studies found no differences in epidermal layer thickness among resistant and susceptible St. Augustinegrass cultivars. However, transmission electron microscopic studies revealed that the cell walls of the sclerenchyma cells around the vascular bundle of southern chinch bug-resistant FX-10 and Captiva were significantly thicker than the cell walls in susceptible Floratam and Palmetto. Our research suggests that the thick-walled sclerenchyma cells around the vascular bundle play a role in southern chinch bug resistance in St. Augustinegrass, possibly by reducing stylet penetration to the vascular tissue.

Resistance to Two Classes of Insecticides in Southern Chinch Bugs (Hemiptera: Lygaeidae)

Abstract Southern chinch bugs were tested from 10 locations in Florida to determine possible resistance to 4 insecticides. Resistance of varying degrees was found in all 4 insecticides: bifenthrin, deltamethrin, imidacloprid, and lambda-cyhalothrin. This study is the first to show southern chinch bug resistance to the latter 3 insecticides. Our data also show that multiple locations are necessary for insecticidal testing for southern chinch bugs since results from 1 location can be very misleading.

Differential Probing Response of Serpentine Leafminer, Liriomyza trifolii (Burgess), on Cos Lettuce

Leaf mining damage by serpentine leafminers, Liriomyza trifolii (Burgess) (Diptera: Agromyzidae), is a major problem of many leafy vegetables especially lettuce. A hierarchy of leaf probing prefere...

New Source of Southern Chinch Bug (Hemiptera: Lygaeidae) Resistance in a Diploid Selection of St. Augustinegrass

Over 400,000 ha of St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze, are managed as a turfgrass in the southern United States, and the southern chinch bug, Blissus insularis Barber, is it...

Romaine lettuce latex deters feeding of banded cucumber beetle: a vehicle for deployment of biochemical defenses

Latex is widely found among plant species and is known to play a defensive role against certain herbivores. Two romaine lettuce, Lactuca sativa L. (Asteraceae) cultivars, ‘Valmaine’ (resistant) and ‘Tall Guzmaine’ (susceptible), were selected to study the potential of latex as a defense mechanism against the banded cucumber beetle, Diabrotica balteata LeConte (Coleoptera: Chrysomelidae). Latex from Valmaine strongly inhibited feeding of adult D. balteata compared to latex from Tall Guzmaine when applied to the surface of artificial diet. Beetles consumed significantly less diet from disks treated with Valmaine latex than they consumed from diet treated with Tall Guzmaine latex, in both choice and no‐choice tests. In a choice test involving diet disks treated with Valmaine latex from young leaves vs. disks treated with latex from mature leaves, the beetles consumed significantly less diet treated with latex from young leaves. No significant difference in diet consumption was found between diets treated with latex from young and mature leaves of Tall Guzmaine in choice tests. Three solvents of differing polarity (water, methanol, and methylene chloride) were tested to extract deterrent compounds from latex; Valmaine latex extracted with water:methanol (20:80) strongly inhibited beetle feeding when applied to the surface of artificial diet. In no‐choice tests, fewer beetles were observed feeding on diet treated with water:methanol (20:80) extract of Valmaine latex than on diet treated with a similar extract of Tall Guzmaine latex, resulting in significantly less consumption of the diet treated with the Valmaine latex extract. These studies suggest that moderately polar chemicals within latex may account for resistance in Valmaine to D. balteata.

Investigation of Seed Treatments for Management of Bacterial Leaf Spot of Lettuce

Chemical seed treatments were evaluated for efficacy of disinfestation of lettuce seed that had been inoculated with Xanthomonas campestris pv. vitians. Three concentrations of each chemical were evaluated by treating seed lots for 5 or 15 min. In addition, the effects of each seed treatment on seed germination and early plant growth were examined by observing seed germination rates. Bacteria were not detected when seed were treated with 3 or 5% hydrogen peroxide for 5 or 15 min. Treatment of seed with 0.52% sodium hypochlorite was relatively ineffective at 5 and 15 min. When sodium hypochlorite was used at a 1% concentration for 15 min, the level of bacterial infestation was reduced to 2%. Suspensions of copper hydroxide plus mancozeb also reduced seedborne inoculum to ≤2%. Treatment of seed with copper hydroxide alone, benzoyl peroxide, or calcium peroxide did not reduce seed infestation levels significantly. Seed germination rates were 90% or greater for the majority of seed treatments tested in laboratory assays. Hydrogen peroxide treatments at a concentration of 5% reduced seed germination up to 28% compared with controls. However, no significant differences in germination were observed among control treatments (noninoculated, nontreated seed and inoculated, nontreated seed) and any of the chemical seed treatments when seed were sown in a pasteurized soil mix in the greenhouse.

Survival of Different Life Stages of the Southern Chinch Bug (Hemiptera: Lygaeidae) Following Insecticidal Applications

Survival of different life stages of the southern chinch bug, Blissus insularis Barber, was measured after insecticidal applications of acephate, chlorpyrifos, and lambda-cyhalothrin. Adults and ny...

EFFECT OF SCREENING METHODS ON EXPRESSION OF ROMAINE LETTUCE RESISTANCE TO ADULT BANDED CUCUMBER BEETLE, DIABROTICA BALTEATA (COLEOPTERA: CHRYSOMELIDAE)

Abstract Resistance in lettuce, Lactuca sativa L., to feeding by adult banded cucumber beetle, Diabrotica balteata (LeConte), was evaluated using three screening methods: leaf disks, excised leaves and intact leaves attached to plants. Dual-choice and no-choice bioassays were used to evaluate each method based on leaf area consumption. Methods of testing had a significant effect on the level of feeding damage by D. balteata on two lettuce cultivars, Tall Guzmaine and Valmaine. Valmaine expressed a significant degree of resistance to D. balteata damage when intact leaf and excised leaf methods were used in dual-choice bioassays between Tall Guzmaine and Valmaine, but the latter failed to show resistant characteristics in no-choice tests when excised leaves were used. Furthermore, there was no significant difference in D. balteata feeding between Tall Guzmaine and Valmaine in the leaf disk tests. Therefore, whole plants are the best method to evaluate lettuce cultivars for resistance to D. balteata. Reduction or cessation of resistance characters in excised Valmaine whole leaves and disks are discussed with references to potential changes in concentration of feeding stimulants and deterrents and changes in latex pressure.

Pepper Varietal Response to Thrips Feeding

Thrips damage to peppers in Palm Beach Co., FL exceeded

Techniques for Differentially Staining Liriomyza trifolii (Diptera: Agromyzidae) Eggs and Stipples within Cos Lettuce Leaves

10 million in 1993, and most was caused by western flower thrips (WFT) and Thrips palmi. Both species feed in flowers, which can lead to poor seed set and fruit distortion. T. palmi foliar feeding causes leaf distortion and shortened internodes. We evaluated thrips density on four types of peppers at three sites in 1992. There was an early preference for flower feeding on sweet pepper varieties. Density increased more rapidly on cubanelle and cayenne types, and they supported larger numbers of thrips with significantly less damage than the other pepper types. Sweet and jalapeno types were very sensitive to foliar and flower feeding.