Abstract
The pine needle gall midge, Thecodiplosis japonensis Uchida et Inouye, is a newly invasive pest in China that mainly harms Pinus thunbergii and P. densiflora. The occurrence and damage caused by T. japonensis in pure stands of P. thunbergii were investigated, and the needle growth and needle compound content were measured. Based on the above steps, the growth dynamics of galls and chemical defense response of P. thunbergii to attack by the gall midge were revealed. The results showed that the adults of T. japonensis in Qingdao city, China, emerged from the end of May to late July, with a peak in mid-June. Needles of P. thunbergii began to differentiate in late June and stopped growing in mid-September. The length of infested needles was 60.17% less than that of healthy needles. On average, there were 9 ± 4 larvae in each gall, 22 at most and 1 at least. The number of larvae within a gall had no significant effect on the size of the gall or larvae. Compared with that in the ungalled tissues, the content of amino acids in the galled pine needle tissues increased by 40.83%, while the content of total polyphenols, tannins, carotenoids, total triterpenes, total alkaloids and other secondary substances decreased to varying degrees, which was favourable for the growth and development of the T. japonensis larvae.
Highlights
There are approximately one million named insects and more than 500,000 plants on Earth, accounting for more than half of the total global b iodiversity[77]
Females search for a suitable host plant (Pinus densiflora or P. thunbergii) and lay eggs on needle pairs of current-year shoots in the vicinity of where they emerge from the soil
It has been shown that phenolic compounds in needles and the resin secreted by host plants can kill the hatched larvae[43,44,47,48]
Summary
There are approximately one million named insects and more than 500,000 plants on Earth, accounting for more than half of the total global b iodiversity[77]. Females search for a suitable host plant (Pinus densiflora or P. thunbergii) and lay eggs on needle pairs of current-year shoots in the vicinity of where they emerge from the soil. Larvae hatch from their eggs after approximately 1 week. It has been shown that phenolic compounds in needles and the resin secreted by host plants can kill the hatched larvae[43,44,47,48] Based on these results, we speculate that there are some very interesting problems that need to be solved: (1) is there a positive correlation between the number of larvae in galls and the size of gall?
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