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Efficacy of the predatory mite Neoseiulus longispinosus (Evans) (Acari: Phytoseiidae) to control the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) on green bean and acceptability of the technology to farmers in Hano
Thesis Abstract:
The study evaluated the efficacy of predatory mite Neoseiulus longispinosus as biological control agent against Tetranychus urticae in green bean through a series of tests starting from constructing its life table construction and analyzing its functional and numerical responses, to determining effective predator-prey ratio under laboratory, greenhouse, and field conditions. It also determined the farmers’ acceptability of using predatory mite to control mite pests by looking into the farmers’knowledge and practices on green bean pest management particularly pesticide use, biological control, nature of spider mite damage, methods of controlling spider mite, and awareness of predatory spider mite.
The life table of N. longispinosus which was studied at 30 ± 1ºC, 80 ± 5 percent relative humidity and with T. urticae as prey showed that the intrinsic rate of natural increase (rm) was 0.2719/female/day; net reproductive rate (Ro), 18.79; cohort generation time (Tc), 12.178 days; doubling time (DT), 2.55 days; and finite rate of increase (λ), 1.31/female/day. All these demographic parameters indicate the capacity of N. longispinosus to increase in number within a short time relative to its prey.
The functional response of N. longispinosus to varying prey density was of type II within satiation point at 30 prey/female/day. The highest number of eggs, larvae, and nymphs consumed by one gravid female per day was 17.2 ± 1.07, 16.8 ± 1.27, and 13.8 ± 1.12, respectively. These consumption rates were detected at prey density of 30–50. In the numerical response study, the maximum number of eggs oviposited by a female predator/day was 4.4 ± 0.91, 4.2 ± 0.84, or 3.8 ± 0.76 eggs when 30 eggs, 40 larvae, or 40 nymphs were given to the predator. On the other hand, when male or female T. urticae was given as prey, the highest number of eggs laid by a gravid female fed was 2.6 ± 0.68 and 2.8 ± 0.63 eggs, respectively.
The most effective predator-prey ratio in the laboratory, greenhouse, and field experiments were 1:33, 1:25, and 1:25, respectively. These ratios were found to suppress the pest mite population while maintaining the predatory mite population up to 25 days after release. These findings could provide basis of the timing and rate of predatory releases for mite control.
The field surveys conducted in Tang My and Son Du hamlets, two of the largest vegetables production areas in Dong Anh District, showed that the respondents in Tang My who had training on vegetable integrated pest management program had higher knowledge on green bean pest management and knew better about natural enemies and biological control than those without training in Son Du. However, both groups of respondents did not have enough knowledge on spider mite control. Most of them did not know or have not heard about predatory mites before. Hence, 40 percent of the respondents said they will not use predatory mites and 33 percent were still uncertain whether they will adopt this biological control.
