Tritrophic Interactions Between an Invasive Weed (Lepidium latifolium), an Insect Herbivore (Bagrada hilaris), and a Plant Pathogenic Fungus (Albugo lepidii).

Perennial pepperweed, Lepidium latifolium L. (Brassicales: Brassicaceae), is an invasive weed that can form dense stands and displace native species. Bagrada hilaris Burmeister (Hemiptera: Pentatomidae) is a serious economic pest of Brassicaceae vegetable crops. Bagrada bug also feeds on L. latifolium and may interact with the plant fungal pathogen Albugo lepidii S.I. (Peronosporales: Albuginaceae) to affect biological control of L. latifolium. A series of laboratory experiments, including Y-tube olfactometer and host-choice tests, were conducted to investigate B. hilaris host-preference behavior. Adults were attracted to the odor of healthy L. latifolium compared with A. lepidii-infected leaves. Bagrada hilaris consistently preferred to feed on healthy L. latifolium when offered both healthy and A. lepidii-infected plants. Experiments were conducted to determine the effects of A. lepidii-infected L. latifolium on B. hilaris survival and development. Survival of all B. hilaris immature stages and adults was markedly reduced for those reared on A. lepidii-infected leaves. Total development time and stage-specific development were faster on healthy L. latifolium leaves compared with A. lepidii-infected leaves. In addition, the ability of B. hilaris adults to passively transmit the rust was studied. Our data demonstrated that B. hilaris could acquire the rust spores while feeding, but it did not passively transmit the pathogen to healthy plants.

Concentration-Response and Residual Activity of Insecticides to Control Herpetogramma phaeopteralis (Lepidoptera: Crambidae) in St. Augustinegrass.

Tropical sod webworm, Herpetogramma phaeopteralis Guenée, is an important pest of warm-season turfgrass in the Gulf Coast states of the United States, the Caribbean Islands, and Central America. Current control recommendations rely on topical application of insecticides against caterpillars. The objective of this study was to generate resistance baseline data of H. phaeopteralis to six insecticide classes. Residual activity of clothianidin, chlorantraniliprole, and bifenthrin was also compared under field conditions in Central Florida. Chlorantraniliprole was the most toxic compound tested (LC50 value of 4.5 ppm), followed by acephate (8.6 ppm), spinosad (31.1 ppm), clothianidin (46.6 ppm), bifenthrin (283 ppm) and Bacillus thuringiensis kurstaki, (342 ppm). In field tests, all compounds at label rates were effective (≥94% mortality of larvae exposed to fresh residues). However, a more rapid decline in activity of clothianidin and bifenthrin was observed compared with chlorantraniliprole. Clothianidin had no statistically detectable activity after 4 wk post-application in spring and the fall, and bifenthrin had no detectable activity after 3 wk in the spring and the fall. However, chlorantraniliprole maintained significant activity (≥84% mortality) compared with other treatments throughout the 5-wk study period. This study provides new information regarding the relative toxicities and persistence of current insecticides used for H. phaeopteralis and other turfgrass caterpillars.

Thermal requirements and development of Herpetogramma phaeopteralis (Lepidoptera: Crambidae: Spilomelinae).

ABSTRACT The tropical sod webworm, Herpetogramma phaeopteralis Guenée is a major turfgrass pest in the southeastern United States. We evaluated larval development on five artificial diets and at six temperatures (15, 20, 25, 30, 32.5, 35 +/- 1 degree C) on St. Augustinegrass (Stenotaphrum secundatum (Walter) Kuntze). Only larvae fed St. Augustinegrass and soy-wheat germ diets completed their lifecycles. None of the artificial diets tested (corn-based, soy-wheat germ, corn cob-wheat germ, corn cob-soy flour, or pinto bean) were suitable for rearing this species, because of high mortality and slower developmental time. Total developmental time (oviposition to adult) on S. secundatum significantly decreased from 47.8 d at 20 degrees C to 21.1 d at 30 degrees C, and then increased to 32.6 d at 32.5 degrees C. Tropical sod webworm failed to complete larval development at 15 and 35 degrees C. The relationship between temperature and developmental rate was described using linear (common and polynomial) and nonlinear models (Briere-1, Briere-2, and Lactin-2). The estimated lower temperature thresholds using a linear model for eggs, first, second, third, fourth, fifth, and sixth instars, prepupa, pupa, and total development were 10.1, 6.9, 12.3, 10.5, 15.3, 13.9, 9.1, 13.1, 12.0, and 13.1 degrees C, and the thermal constant of these stages were 62.9, 66.2, 38.2, 40.3, 24.9, 32.3, 51.9, 106.4, 109.9, and 370.4 degree-days, respectively. The Briere-1 model provided the best fit with estimated lower, upper, and optimum thresholds for total development of 14.9, 34.3, and 29.4 degrees C, respectively. The developmental requirements of H. phaeopteralis can be used to help predict the distribution and seasonal phenology of this pest.