Mohammad H. Badii

Effect of different densities of the twospotted spider mite Tetranychus urticae on CO2 assimilation, transpiration, and stomatal behaviour in rose leaves.

The effect of population density of Tetranychusurticae Koch on CO2 assimilation, transpiration and stomatal behaviour in rose leaves and on the diameter and length of stems and flower buds was investigated under greenhouse conditions. The investigation was performed in order to gain more insight into integrated control systems in rose crops grown under greenhouse conditions. Physiological processes, such as photosynthesis and transpiration, as well as stomatal behaviour and chlorophyll content, were studied as they form part of the plants nutrition mechanism and therefore affect the quantity and quality of the flowers. Information related to the effect of spider mite population density on bloom quality, diameter and length of stems and flower buds was also collected. The data indicate that increased mite density coincides with a decrease in the net photosynthetic rate, transpiration and chlorophyll content. Higher mite densities on leaves cause stomata to remain open for longer periods, which allows a greater loss of water. Spider mite densities of 10 and 50 mites per leaf cause a reduction in flower stem length of 17 and 26%, respectively, as compared to plants with no mites present.

PRICKLY PEAR CACTI PESTS AND THEIR CONTROL IN MEXICO

Opuntia spp., known by Mexicans as nopal, represents historically one of the most important biotic elements of Mexico. This natural resource has been and is being used for multiple purposes. Some of the current uses include: food for humans as both vegetable and fruit, forage for animals, source for alcoholic beverages, sweetener, live fences, industrial products such as cosmetics and dye, and as a medical source against diabetes and other diseases. Its cultural and natural values have been reflected in paintings, ancestral Indian codes, and old writings; thus its historic relevance is quite apparent. Furthermore, it is depicted both in the Mexican national seal and flag where it represents the very characteristic feature of Mexican culture and society. Opuntia spp. are distributed throughout the American continent and Mexico is considered a center of diversity as these species are well adapted to the arid and semiarid conditions of Mexico. Here we summarize and discuss briefly the most important insect pest species and one snail species which currently are considered as serious pests of cultivated Opuntia spp. in Mexico, and, thus require control measures. The control of these pest species is mainly through chemical pesticides and currently at least a dozen types of insecticides are being applied.

Temperature-based life history and life table parameters of Texas citrus mite on orange (Acari: Tetranychidae)

Abstract The effect of five different constant temperatures on life history and life table parameters of the Texas citrus mite Eutetranychus banksi (McGregor) on sweet orange (Citrus sinensis (L.) Osbeck) leaves was studied under controlled laboratory conditions. The intrinsic rates of natural increase were -0.0649, 0.1723, 0.1759, 0.1973, and -0.0711; net reproductive rates, 0.30, 8.25, 7.24, 9.21, and 0.44; mean generation times, 19.21, 12.79, 11.74, 11.52, and 11.64 days at 20, 25, 30, 32.5, and 35°C, respectively. In general, the durations of each immature instar as well as combined immature stages, declined with increasing temperature up to 32.5°C and then increased at 35°C. As regards the adult stages, the durations of preoviposition, oviposition, and postoviposition periods, as well as adult longevity, decreased with rising temperature in the range of 25–30°C. With the exception of the preoviposition period, temperature of 20°C had an opposite effect on the durations of the remaining adult phases.Mean total andmean daily fecundities generally but irregularly declined with ascending temperatures.Mean total developmental times declined curvilinearly with rising temperature; however, the rate of development had a positive curvilinear relationship with increasing temperatures. Threshold temperature of development (°C) and thermal constants (degree-days) for egg, larva, protonymph, deutonymph, combined immature stages, preoviposition, oviposition, postoviposition, and adult longevity were: 5.82, 127.66; 3.29, 14.08; 4.33, 41.91; 3.69, 53.28; 4.08, 279.02; 5.35, 34.39; 3.06, 86.78; 3.75, 28.14; and 2.89; 139.52, respectively. From the data it was calculated that there are 22–23 annual generations of the Texas citrus mite in Tamaulipas, Mexico. Temperatures in the range of 28 to 31°C constitute the optimal range for development of this mite species.

Esterases in Aedes albopictus (Skuse) from Northeastern Mexico

Abstract. A microassay was used to determine the activities of &agr;- and &bgr;-esterases and acetyl Cholinesterase in larvae and adults of populations of Asian tiger mosquito, Aedes albopictus (Skuse) (Diptera: Culicidae), in northeastern Mexico. Main collection sites were cemeteries and tire dumps. Three mechanisms of resistance were determined; however, elevated &bgr;-esterase activity was prominent, with frequencies greater than 92% in adult Asian tiger mosquitoes in three of the populations. Based on these results, we concluded that the mechanisms of resistance in the populations studied are caused mainly by esterase activity. This study can serve as a reference for future programs aimed at controlling this species.