Helopeltis bradyi is the main pest of tea plants. Ecological characteristics of this pest are important to be understood to support the development of their management and control measures. This study aimed to determine the coexistence and vertical distribution pattern of H. bradyi and its predator, Oxyopes javanus, on tea plant parts. The study was conducted at the PT Pagilaran tea plantation in Central Java, in the 2018 rainy season. Population observations were carried out in situ on 20 infested sample-trees taken randomly, for 10 consecutive days, in the morning, at noon, and in the afternoon. Vertical distribution patterns were determined based on Poisson dispersion index (DI), negative binomial, and Green index (GI). The results showed that the O. javanus spider was found preying on H. bradyi. Coexistence between this pest and predator in the same part of the plant, the pest, and the predator, occurred in the morning were 50.0, 42.8, and 7.2%; at noon were 58.3, 41.7, and 0%; and at the afternoon were 66.7, 33.3, and 0%, respectively. The parts of the plant for the coexistence are pekoe leaves; the 1st, 2nd, 3rd, and 4th of young leaves; and 1st of older leaves. The pattern of vertical distribution in the morning, at noon and in the afternoon for H. bradyi was the weak clump, while for O. javanus was uniform. The ratio of predator: prey in the morning, at noon and in the afternoon was 1:10.7, 1:16.7, and 1:10.0, respectively.

Behavioural characteristics of the tea mosquito bug, Helopeltis bradyi, are important to be understood to support the control efforts of the pest. The study was aimed to describe population structure and behaviour of H. bradyi on the tea plant parts. The field study was conducted at Pagilaran tea plantation located in Batang Regency, Central Java Province, at 870 m asl, in early dry season of March – April, 2018. All developmental stages of H. bradyi on tea plant parts of 20 sample plants were observed and recorded in situ in the morning, at noon, and in the afternoon. Results showed that nymphs dominated the H. bradyi population structure. Population density in the morning (06.00-08.00 a.m.) was 45.1 individuals/20 plants (5.54% eggs, 80.71% nymphs, 13.75%adults), at noon (11.00 a.m.-13.00 p.m.) was 41.7 individuals/20 plants (3.40% eggs, 84.00% nymphs, 12.60% adults), and in the afternoon was 37.0 individuals/20 plants (0% eggs, 88.38% nymphs, 11.62% adults). The H. bradyi was mostly present on tea shoots at upper leaf surface namely 97.08% in the morning, 79.27% at noon, and 88.14% in the afternoon, the rest was on lower leaf surface, shoot internodes, and other plant parts. The eggs were only found on tender internodes of shoots.