A community approach to the eggplant integrated pest management in central Taiwan

• Main Authors: Li-Hsin Huang, 黃莉欣
• Other Authors: 陳秋男
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/98010003209010498547

博士 === 國立臺灣大學 === 昆蟲學研究所 === 94 === I studied the community structure of arthropod herbivores and predators on eggplant (Solanum melongena L.) in central Taiwan. The leaves, flowers and fruits of eggplant were sampled, among them, the leaves were divided into spire leaves and expanded leaves. The insects and mites were identified to their families and their numbers counted. Relative abundance and cluster analysis indicated that Thripidae, Aphididae, Aleyrodidae, Tetranychoidea and Tarsonemidae were common herbivores on the eggplant. Phytoseiidae was the major predator, followed by Anthocoridae, Miridae and Cecidomyiidae. Tetranychoidea and Aleyrodidae mainly inhabited on the moderate and aged leaves. Tarsonemidae preferred the spire leaves and the calyx of fruit to the expanded leaves and flowers. The color of spire leaves turned dark green and tissue became thickening after injury by Tarsonemidae, so that the eggplant growth was obstructed. Thripidae frequently occurred on leaves, flowers and fruit of eggplant and they were more prevalent than others. Injury of flowers and fruit by Thripidae caused the flowers to fall and fruits with some white or brown narrow strip scars and deformities, hence decreasing yields and marketability of the eggplant. Therefore, I suggested both of Thripidae and Tarsonemidae were two key pests on the eggplant. Thrips palmi Karny was the dominant species in Thripidae and Polyphagotarsonemus latus Banks the only species of Tarsonemidae found on eggplant. The differences in crop management practices could drastically affect the insect-mite community in eggplant fields. The family richness in the eggplant field with pesticides application was lower than the weeded one. The more the pesticides applied, the less was the evenness, and hence the biological diversity was lower. The fluctuation of predators in plot without pesticides application was more stable than that with pesticides application. The niche breadth of Acaroidea and Typhlocybidae in eggplant plot without pesticides application were the widest, indicating that these two families distributed evenly on each parts of eggplant. Aleyrodidae, Agromyzidae and Tetranychoidea mainly concentrated on the expanded leaves. Therefore, their niche breadth was narrower. The niche breadth of Tarsonemindae and Phlaeothripidae in plot with pesticides application was wider than that in the plot without pesticides application. However, those of other herbivores were in the contrary. Analysis revealed that Thripidae, Aleyrodidae, Typhlocybidae, Aphididae, Noctuidae, Agromyzidae and Tetranychoidea had higher niche overlap. This result suggested that resource utilization of these herbivores on three parts of eggplant was very similar. In predator both of Anthocoridae and Miridae had higher niche overlap. Niche overlap of Scolothrips indicus Priesner, with Cecidomyiidae was 98.8%. It is also noted that the niche overlap between all predators and Tarsonemidae was the least, suggesting that there were no predators against Tarsonemidae in the eggplant fields. From the view of injury-damage type, I tried to use feeding guild to group the herbivores as chewers, sucking-insects, sucking-mites and internal suckers in order to develop a practical sampling technique for the eggplant IPM program. The fluctuation trend of the value of s2/m and Lloyd’s mean crowding (m*) of various feeding guild weekly was the same as the ones of single population, but they were different on index of patchiness (m*/m). The index weekly was partly less than 1.0 for single population in plot with pesticides application; however, the index weekly was all more than 1.0 for feeding guild. Taking the data collected from plot without pesticides application to estimate the optimal sample size for density ranging from 5 to 200 individuals on each part of eggplant according Taylor’s power law, it indicated that the sample size required for expanded leaves was the most. When there are 10 individuals on an expanded leaf, we need to sample 257, 649, and 209 leaves for Thripidae, Aphididae, and Aleyrodidae, respectively. When to estimate sucking-insects on expanded leaves, 123 expanded leaves have to be sampled based on 10 individuals per leaf. The results showed that the optimal sample size of the feeding guild was lower than single population. Because T. palmi was the key pest on eggplant, special attention was also paid to the effect of temperature on its life history traits and population parameters. Cohorts of T. palmi were reared on eggplant leaf at 15, 21, 25, 30 and 35℃ in growth chambers for three generations continuously. The results showed that survival rate of T. palmi from egg to adult was only 4 - 8% at 35℃, and the adult female and male lived only 2.9 and 2.8 days, respectively, without laying any eggs. Under the four temperatures the pre-adult stage took respectively 29.9, 19.6, 12.3, and 10.4 days to complete the development. The longevity of adult female became shorter as the rearing temperature increased, being 21.6, 20.2, 15.4 and 9.7days, respectively. The female had the highest fecundity (57.1 eggs/female) at 25℃, but its oviposition period was the shortest (ca. 21 days). A simple linear regression of developmental rate on temperature ranging from 15 to 30℃ showed that the lower developmental threshold (T0) was 7.7℃ (SE = 0.2℃) and the cumulated effective temperature ( K) was 227.2°D (SE = 3.3°D) for T. palmi to complete development from egg to adult. Based on the above value of T0 and K, and the 1999 to 2002 meteorological data of the Taiwan Agr. Res. Inst. at Wufong, we estimated that this thrips could complete 25 to 26 generations a year in central part of Taiwan. The results indicated that the age-specific fecundity ( mx ), the daily fecundity (fx5 ), and the age-specific maternity ( lxmx) was highest at 25℃. The intrinsic rate of increase (r) rose from 15, to 21 to 25℃, and fell at 30℃, being 0.033, 0.046, 0.157, and 0.118 day-1, respectively. The net reproductive rate (R0) was highest at 25℃ at 18.6 eggs. The mean generation time (T) shortened gradually from 15 to 30˚C; at 30℃ it was only one day shorter than 25℃. Consequently, we concluded that 25-30℃ is optimal for population growth of T. palmi on eggplant.