Effects of sublethal concentrations of Vectobac on biological parameters of Aedes aegypti.

The effect of sublethal concentrations (30% lethal concentration [LC30] = 0.41 ppm, LC50 = 1.04 ppm, and LC70 = 2.60 ppm) of VectoBac 12 aqueous suspension (AS, Bacillus thuringiensis var. israelensis H-14, 600 ITU/mg) on life parameters of Aedes aegypti and its F1 progeny (not exposed) was assessed in laboratory tests. Based on the data, it was clear that concentrations of 0.41 ppm of VectoBac significantly shortened the duration of the developmental cycle of the exposed mosquitoes, but not that of the F1 (not exposed). Significant differences were found among the proportions of the age-specific survival between each toxic level, whereas the control did not differ from the treated individuals at the LC50 and LC70. The survival curves of the F1 showed significant differences among the different treatments and with the control. A significant effect was found on the fecundity of adults. Age-specific fecundity was markedly lower for the LC50 and LC70 treatments compared to the LC30 treatment and the control. In general, life parameters were affected inversely and significantly at higher concentrations of VectoBac, both in the exposed population of Ae. aegypti and in the F1 (not exposed).

Prey stage preference and functional response of Euseius hibisci to Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae).

The aims of this study were: (a) determine the prey stage preference of female Euseius hibisci (Chant) (Phytoseiidae) at constant densities of different stages of Tetranychus urticae Koch (Tetranychidae), (b) assess the functional response of the predator females to the varying densities of eggs, larvae, or protonymphs of T. urticae, and (c) estimate the functional response of E. hibisci when pollen of Ligustrum ovalifolium was present as well. We conducted experiments on excised pieces of strawberry leaf arenas (Fragaria ananassa) under laboratory conditions of 25+/-2 degrees C, 60+/-5% RH and 12 h photophase. Our results indicated that the predator consumed significantly more prey eggs than other prey stages. Consumption of prey deutonymphs and adults was so low that they were excluded from the non-choice functional response experiments. The functional response on all food items was of type II. The two parameters of the functional response were estimated for each prey type by means of the adjusted non-linear regression model. The highest estimated value a' (instantaneous rate of discovery) and the lowest value of Th (handling time, including digestion) were found for the predator feeding on prey eggs, and a' was lowest and Th highest when fed protonymphs. Using the jack-knife method, the values for the functional response parameters were estimated. The values of a' and Th produced by the model were similar among all prey types except for the eggs, which were different. Using pollen simultaneously with prey larvae decreased the consumption of the latter over the full range of prey densities The suitability of this predator for biological control of T. urticae on strawberry is discussed.

Laboratory evaluation of Vectobac as against Aedes aegypti in Monterrey, Nuevo León, Mexico.

Intensive use of the organophosphate insecticide malathion against adults and temephos against larvae of Aedes aegypti in Mexico over the past 30 years has led to problems requiring the use of new larvicides. Toward this objective, Bacillus thuringiensis var. israelensis (Bti), a target-specific and environmentally safer control agent, was evaluated. Laboratory bioassays were done to determine the susceptibility of 2nd- and 3rd-stage larvae of Ae. aegypti to Vectobac 12 AS (aqueous suspension, 600 ITU/mg). A median lethal concentration of 0.0104 ppm and a 95% lethal concentration of 0.18 ppm were determined after 24 h of exposure to the agent. The values obtained were adjusted for field application and were further tested in the field by the State of Nuevo León, Mexico Vector Control Program. Suspensions of Bti were poured into pipe-water trucks and transferred to domestic 200-gal metal water drums. Larval populations were reduced during a 2-week study period. However, residents complained about a fine dusty film on the water surface. Nevertheless, these results are promising for future Bti field applications.