MSc

Vegetable crops are subjected to attack by a number of mite species leading to heavy economic loss. However, information on the diversity of phytophagous mites affecting major vegetable crops in Kerala is limited. Considering this, the proposed study entitled ‘Diversity of phytophagous mites and their natural enemies in vegetables’ was undertaken to develop a database on the important acarine species associated with major vegetable crops in Thrissur district, Kerala. The study was carried out in the Department of Agricultural Entomology, College of Horticulture, Vellanikkara during 2011-2012. The main objectives of the study were to identify the species composition of phytophagous and predatory mites associated with brinjal, okra, amaranthus, cowpea, chilli and bitter gourd from various localities of Thrissur district and also to study the spatial and temporal dynamics of population of phytophagous mites in these vegetable crops.
A total of 19 species of phytophagous and predatory mites belonging to eight families in two suborders were identified. Tetranychidae, Tenuipalpidae and Tarsonemidae were the major phytophagous mite families recorded in the study. Tetranychus was found to be the dominant phytophagous mite in brinjal, bhindi, amaranthus and cowpea, whereas in chilli and bitter gourd, the tarsonemid mite, Polyphagotarsonemus latus (Banks) was the predominant one.
The predatory mites associated with vegetables belonged to five families viz., Phytoseiidae, Stigmaeidae, Tydeidae, Cunaxidae and Bdellidae, among which Phytoseiidae predominated. The important phytoseiid predators observed in the survey included Amblyseius paraaerialis Muma, Paraphytoseius orientalis Narayanan, Neoseiulus longispinosus (Evans), Phytoseius sp., Euseius macrospatulatus Gupta, Typhlodromips sp. and Scapulaseius sp. The predatory mite Tydeus sp. of the family Tydeidae, Cunaxa sp. of the family Cunaxidae and Bdella

sp. of the family Bdellidae were found in chilli. The Stigmaeid mite of the genus Agistemus was found in brinjal, bhindi and chilli.
The comparison of different diversity indices in various crop ecosystems revealed that brinjal had highest genus richness. The value of Simpson-Yule Diversity index (D) was highest for brinjal which indicated that brinjal supported maximum genera of mites. The minimum value of D was in bitter gourd suggesting that it was least favoured by mites. Similarly the value of Shannon – Weaver Diversity index was found to be highest in brinjal and the least in bitter gourd. This shows that brinjal is favoured by a large number of mite species as compared to bitter gourd. The Berger – Parker dominance index (d) was worked out for the most dominant genus in the respective ecosystem and it was found that Tetranychus was the most dominant genus in brinjal, bhindi, cowpea and amaranthus where as P.latus was the dominant one in chilli and bitter gourd.
The study on the population dynamics of mites in vegetables revealed that the mite population increased during hot summer months. The mite population was at their lowest from June to September as they were washed off due to heavy and consistent rainfall. After the cessation of rainfall, the mite incidence increased again and attained a second peak during December to January.
The distribution pattern of mites on the plants varied with the canopy level and it was found that tetranychid mites preferred matured leaves of middle canopy in brinjal and amaranthus but bottom canopy in cowpea. In bhindi, there was no significant difference in the distribution of mites at the three canopy levels. The distribution of P.latus in chilli and bitter gourd was restricted to the top canopy leaves alone.
Weather factors such as rainfall and evening relative humidity showed highly significant negative correlation with mite population, whereas maximum temperature showed highly significant positive effect on the population of mites. Hence it is evident from the study that increase in temperature coupled with decrease in relative humidity favoured an increase of mite population.