Abstract
The population growth and its causes of red mite, Tetranychus bioculatus (Wood-Mason), demographic features on host plants, functional response of predators and bioefficacy of pesticides and botanicals were studied on ornamental plants in the laboratory and gardens for two years from 2004 to 2006. T. bioculatus was the most abundant in January with peak population of 1411 and 858 mites per marigold plant in two years due to increasing temperature and decreasing humidity. The damage to marigold plants was at least 55 per cent reaching almost cent per cent in some gardens in January and February which was favourable for positive growth of mite population. Correlation of both population and infestation rate of red mite with prevailing temperature was significant. The dispersal of red mite was quite apparent following heavy infestation to the marigold plants from January to March due to its increase in large numbers and the presence of spider predators. The different ornamental host plants such as marigold, rose and cosmos significantly influenced the life table parameters of T. bioculatus showing the highest net reproductive rate (\(\text{R}_{\text{o}}\)) of 78.69 in mean generation time (GT) of 18.22 days and innate capacity of increase (\(\text{r}_{\text{m}}\)) of 0.24 was obtained on marigold. Among different species of predators, spiders and Micraspis discolor were dominant with comparatively small numbers of Stethorus punctillum found in association with red mites. Positive correlations were noticed in the predator-prey relationship. The grubs and adults of S. punctillum were more active for searching and consuming different stages of prey. The predation efficiency of S. punctillum and M. discolor was significantly higher (ranged from 35.4 to 48.4 per day) when feeding on eggs, than feeding on larvae, nymphs and adults of the mite. The toxicities (LD₅₀ and LD₉₀) were different among acaricides and insecticides in the laboratory study of red mite, and significantly different killing effects of these pesticides were found in the garden. Talstar at 0.0025% and Dimethoate at 0.005% were most effective for the control of red mite in marigold garden. The crude leaf extracts of biskatali (Polygonum hydropiper), neem (Azadirachta indica), nishinda (Vitex negundo), akanda (Calotropis gigantia) and pithraj (Aphanamixis polystachya), and oils of neem and pithraj showed significant differences in killing adult red mites in both laboratory and garden. The leaf mixtures of 6% biskatali and neem, and 0.6% neem oil were the most effective botanicals for killing 82-100 per cent mites and might be an important control option for this mite in ornamental ecosystem.