Response of Lobesia botrana to different developmental stages of grape

Abstract：【Objective】Lobesia botrana (Denis & Schiffermüller), an imported plant quarantine pest, was first discovered in Gaochang District, Turpan City, Xinjiang, China in 2014. Up to now, L. botrana has spread to the most areas of Turpan City, China. The pest has five generations in a year in Turpan. The first and second generations of larvae damage the grape inflorescences and immature fruits, and the number of occurrences is low, while the third and fourth generations of larvae damage the mature fruits, and the number of occurrences shows a trend of outbreak. The study aimed to clarify the effects of different developmental stages of grapes on the occurrence of L. botrana, explore the relationship between the nutrient contents of the grapes in the different developmental stages and field quantity changes, growth and reproduction of the pest, so as to reveal the reasons for the outbreak of the third and fourth generations of L. botrana in the field.【Methods】The early-instar larvaes were collected from the occurrence area of L. botrana and brought to the laboratory for artificial feeding. The larvaes were fed with the grape inflorescences, immature fruits and mature fruits, respectively. Under the same conditions, the growth indexes, development duration, oviposition amount and nutrient changes of the larvaes and pupaes were measured. The correlation between these nutrient changes and the number of L. botrana in the field and its indoor growth, development and reproduction was analyzed.【Results】The 3rd, 4th and 5th instar larvaes feeding on the immature fruits and mature fruits had higher body weight, body length and body size than those feeding on inflorescences, and the test operation greatly increased the mortality of the early-instar larvaes, and the average weight of the pupaes feeding on the mature fruits was also relatively high; according to the developmental duration of each stage, the egg duration, larvalduration and pupal duration of individuals feeding on the mature fruits were 6.43 d, 11.80 d and 6.08 d, respectively, which were shorter than those feeding on inflorescences (7.76 d, 13.44 d, 7.31 d).On the contrary, the results of the adult longevity were opposite, and the adult individuals feeding on the mature fruits survived longer. In terms of the sex ratio, there was no significant difference in the sex ratio of pests feeding on the inflorescences, immature fruits or mature fruits, but the number of the females was always higher than that of the males. There were significant differences in the number of eggs laid by the females under different sex ratios. No matter how the sex ratio changed, the number of eggs laid by the females feeding on the mature fruits was always higher than that feeding on the inflorescences, and the number of eggs laid by the females was higher under the mating conditions of 3∶3, 4∶4 and 5∶5, and the number of eggs laid by the single females feeding on the inflorescences was no more than 15 under the same mating conditions. The total survival rate of L. botrana feeding on the inflorescences was 29.17%, which was significantly lower than that of feeding on the young fruits (47.50% ) and mature fruits (61.60%). Through the detection of nutrient changes in the feeding materials, the protein content from high to low was the inflorescences＞mature fruits＞immature fruits, the soluble sugar content from high to low was the mature fruits＞immature fruits＞inflorescences. The soluble sugar content in the mature fruits was 10 times as much as that in the inflorescences and 3 times as much as that in the young fruits. The contents of the total amino acids, vitamin C and macroelements in the inflorescences were higher than those in the immature and mature fruits. The contents of the flavonoids and tannins in the inflorescences were the highest, and the contents of the flavonoids and tannins in the mature fruits were minimum. The correlation analysis showed that the soluble sugar was significantly and positively correlated with the number change, oviposition and survival rate of L. botrana, while the protein, amino acid, tannin and flavonoids were significantly and negatively correlated with the oviposition and survival rate of L. botrana.【Conclusion】Grapes in the different developmental stages, as the main food source of the larvaes, had different effects on the growth and development of L. botrana. Compared with the grape inflorescences and immature fruits, the nutrients in the mature fruits were more suitable for the growth, development and reproduction of L. botrana. The substances in the mature fruits could promote the growth and development of L. botrana larvaes, improve their survival rate and fecundity, while the grape inflorescences contained a large number of secondary substances to inhibit the growth and development of L. botrana larvaes. Therefore, the growth and development stages of grape would be the key factors affecting the population changes of L. botrana.