Effects of different leek cultivars on the growth, development and fecundity of Bradysia difformis Frey

Bradysia difformis Frey is an important pest of economic crops, which causes leeks production heavily reduction. It is important for prediction, prevention of B. difformis, and selection of leek cultivars resistant to B. difformis to research the growth, development and reproductive rhythm of B. difformis on different leek cultivars. An experiment was conducted in an artificial climate chamber with temperature of (25±1) ℃, dim light of 125 lux and relative humidity of 80%. Twenty selected leek cultivars from different areas of China were used as the tested plants. The developmental duration, whole generation duration, adult longevity, fecundity and survival rate of B. difformis on different leek cultivars were investigated. Life table of B. difformis on 20 leek cultivars was established, and the population parameters, such as intrinsic rate of increase (r_m), net reproductive rate (R₀), mean generation time (T), population doubling time (t) and finite rate of increase (λ) were calculated. The results indicated that B. difformis could complete its growth and development on twenty leek cultivars. The duration of whole generation of B. difformis was longest on ‘Wanyuan Purple Root with wide leaves’, followed by ‘Snow 791 with wide leaves’ and ‘Wanyuanhanzhong winter leek 1’. The shortest duration of whole generation of B. difformis was on ‘Pingjiu 2’, followed by ‘Jiuxing 2’ and ‘Hanzhong Purple Root Leek’. Females’ longevity was higher than males’ longevity on different leek cultivars, and the average eggs per female spawning was positively correlated with the female longevity. Especially for leek cultivars of ‘Wanyuanhanzhong winter leek 1’ and ‘Pingjiu 2’, their females’ longevities were respectively 2.18 d and 2.44 d, and average eggs per female spawning were 56.00 and 101.25, respectively. The survival rates of B. difformis decreased with development. The survival rate of each instar was highest on ‘Jiyanxiaojiuyuan’, and lowest on ‘Wanyuanhanzhong winter leek 1’, and was relative higher on ‘Pingjiu 2’ too. The survival rates of eggs, larval, pupa and adult were 100%, 90%, 85% and 85% on ‘Jiyanxiaojiuyuan’; 62%, 32%, 25% and 25% on ‘Wanyuanhanzhong winter leek 1’; and 100%, 85%, 82% and 80% on ‘Pingjiu 2’; respectively. The analysis of life tables of B. difformis on different leek cultivars showed that the intrinsic rate of increase, finite rate of increase were highest on ‘Pingjiu 2’, which were 0.22 and 1.25, respectively. They were smallest on ‘Wanyuanhanzhong winter leek 1’, 0.07 and 1.07. The population doubling time showed opposite trend, it was shortest on ‘Pingjiu 2’ (3.15 days) and longest on ‘Wanyuanhanzhong winter leek 1’ (10.20 days). The other cultivars were fall in between for the three parameters. Based on the above results, B. difformis had the best adaptability and palatability on ‘Pingjiu 2’, and could heavy damage the cultivars; while it developed worst on ‘Wanyuanhanzhong winter leek 1’ with lighter damage for the cultivars.