Study on the Repellent Effects of Different Grass Species on Raspberry Drosophila melanogaster

Zhe CHEN Qunying ZHANG Dingyuan YANG Xilong SHEN

Abstract Large leaf mint （Agastache rugosus）， white clover （Trifolium repens）， spearmint （Mentha spicata）， tall fescue （Festuca elata）， orchardgrass （Dactylis glomerata） and alfalfa （Medicago sativa） were selected to perform sod culture， and the repellent effects of different grass species on adult raspberry Drosophila melanogaster were studied， so as to provide a scientific basis for grass cultivation in the control of raspberry fruit fly. The study showed that spearmint and big leaf mint had strong repellent effects on raspberry D. melanogaster， with repellent effects reaching 81.25% and 72.73%， respectively， and could be promoted as the main plant varieties in grassing orchards; and the next was alfalfa and white clover， which had the average repellent effects of 50.57% and 34.94% on D. melanogaster， respectively， and could be used as nectar plants to supplement the ecosystem of the sod culture orchards.

Key words Orchard green covering; Raspberry fruit fly; Repellent effect

Raspberry （Rubus corchorifolius） is a plant in Rubus of Rosaceae. The fruit is sweet and sour and has a unique flavor. It is the third-generation fruit that has swept the world and has high nutritional value and commercial value[1]. In recent years， with the growing area of raspberries in Guizhou， the problem of pests and diseases has become increasingly serious. Among them， raspberry fruit fly has become the most serious pest that damages the quality of local raspberries. After investigation， it is found that Drosophila melanogaster that damage raspberries are mainly D. melanogaster， which belongs to Drosophila in Drosophilidae[2]， and is harmful to Chinese bayberry （Myrica rubra）[3]， cherry （Cerasus pseudocerasus）[4]， blueberry （Vaccinium spp）[5] and other fruits. The outbreak period of fruit fly coincides with the peak season for fruit picking， and chemical control is more difficult. At present， the trapping of fruit fly mainly relies on sugar-acetic acid solution[6] and sticky insect board[7]， but the control effect is limited. Some developed countries have not only improved the ecological benefits of orchards by developing sod culture models， but also effectively curbed the spread of pests and diseases， which is worth learning[8]. Among the common ways of growing grass， spearmint （Mentha spicata）， large leaf mint （Agastache rugosus）， white clover （Trifolium repens）， and alfalfa （Medicago sativa） all show certain insect repellent effects[9-12]， and the highly adaptable grass species， orchardgrass （Dactylis glomerata） and tall fescue （Festuca elata）， are also widely used in grassing orchards. However， the insect repellent effects of these herbaceous plants on raspberry D. melanogaster remain to be verified. In this study， the repellent effects of these 6 herbaceous plants on raspberry D. melanogaster were investigated， aiming to provide a scientific basis for the promotion of the sod culture model in raspberry orchards.

Materials and Methods

Materials

The test site was located in the Raspberry Base of Xinchang Town， Wudang District， Guiyang City， Guizhou Province. This area is a subtropical monsoon humid climate zone with no intense heat in summer， no severe cold in winter， abundant rainfall， and four distinct seasons. The altitude is 1 200-1 400 m; the annual average temperature is 14 ℃; the annual rainfall is 1 200-1 500 mm; the relative humidity is about 80%; and the frost-free period is 289 d. The test materials included spearmint， large leaf mint， white clover， alfalfa， orchardgrass and tall fescue， a total of 6 grasses. The weight of seeds of each grass was 5 kg， purchased from Beijing Zhengdao Ecological Technology Co.， Ltd.

Methods

Sowing

Referring to similar orchard grass growing methods[13]， in late October 2018， raspberry planting areas with the same terrain and good drainage in the field were selected， and grass seeds were sown between rows， with a width of 1.5 m. Meanwhile， organic fertilizer was applied at 15 000 kg/hm2 and covered with soil， followed by irrigation. The germination of grass seeds in grass-growing test areas was observed every 1 week， and the seedlings were properly supplemented while pulling up other weeds other than the target grass. In the clear culture area， all the weeds in the area were removed by a rotary tiller and manual weeding in early spring. In late June 2019， the raspberry entered the flowering period when topdressing was required， and 12 000 kg of organic fertilizer was applied to each hectare in the grass growing area. When the grass species in the grass growing areas grew evenly， yellow sticky boards were used to start recording the quantity of D. melanogaster.

Statistics of fruit fly quantity

In late June 2019， we started to record the number of D. melanogaster in the 6 kinds of grass test area and the clear culture area. A yellow sticky insect board was hung at the center of the raspberry branch 1.2 m from the ground， facing north-south. The sticky boards were arranged with a distance of 2 m， 10 boards per group， and 3 groups were set for each grass growing area. The clear culture area was a blank control. The number of D. melanogaster trapped by the sticky boards every 7 d was counted， and the boards were replaced and supplemented with new sticky insect boards in time. The statistics of this experiment ended in late September 2019， at the full bearing period. The changes in the number of D. melanogaster in the grass-growing areas and the clear culture area were analyzed and compared， and SPSS 22.0 statistical software was used to analyze the significance of the repellent effects of different grasses.

Repellent effect=[1-（Average number of D. melanogaster in grass-growing area/Average number of D. melanogaster in the clear culture area）]×100%

Results and Analysis

Changes in the number of raspberry D. melanogaster in different periods

Fig. 1 shows the changes in the number of D. melanogaster in the grass-growing areas and the clear culture area in different periods. The numbers of D. melanogaster in the grass-growing area and the clear culture area both increased first and then decreased. After the raspberry entered the flowering period in late June， the number of D. melanogaster gradually increased. When the raspberry entered the fruiting period in late July， the number of D. melanogaster increased rapidly， until it reached the maximum during the fruiting period of raspberry in early August. In the clear culture area， a single group of sticky insect boards （10 sheets） recorded the highest average number of D. melanogaster as 590， and then with the end of the full bearing period， the number of D. melanogaster gradually decreased. By late September， a single group of sticky insect boards recorded 80 D. melanogaster.

Among the 6 kinds of grass treatments， spearmint had the strongest repellent effect on D. melanogaster. The number of D. melanogaster on a single group of sticky insect boards in each period was less than 90， and it dropped to 10 in late September， indicating the most significant repellent effect to D. melanogaster. The next was big leaf mint， and the number of D. melanogaster recorded by a single group of sticky insect boards was 130 at the beginning of August， and at the end of September， the number of D. melanogaster was 20. In addition， alfalfa and white clover also showed a certain ability to repel D. melanogaster. The numbers of D. melanogaster at the peak were 270 and 400， respectively， and at the end of September， the numbers of D. melanogaster were both below 50.

In this study， tall fescue and orchardgrass had the worst repellent effect on D. melanogaster， and the changes in the number of D. melanogaster recorded on the sticky insect boards were basically the same as those in the clear culture area. From the flowering period to the end of fruiting， the number of D. melanogaster recorded in the tall fescue-growing area exceeded the number of D. melanogaster in the clear culture area by many times， and reached 600 in a single group at the peak. The number of D. melanogaster in the orchardgrass area was slightly lower than that in the clear culture area， and the maximum number of flies was 550.

The repellent effect of various grass treatments on raspberry fruit fly

The total number of D. melanogaster trapped by a single group of sticky insect boards was counted in each grass growing areas and the clear culture area in the third quarter （late June to late September）， and the repellent effect of each grass was calculated. The results showed that spearmint had the strongest repellent effect on raspberry D. melanogaster （81.25%）， followed by big leaf mint （72.73%）， and the difference between the two was not significant. In addition， the repellent effects of white clover and alfalfa on D. melanogaster were 50.57% and 34.94%， respectively， which were extremely different from those of spearmint and big leaf mint. The orchardgrass and tall fescue had the smallest repellent effects， 34.94% and 10.23%， respectively. The difference between the two was not significant， but the differences were extremely significant from other treatments except the control （Table 1）.

Conclusions and Discussion

This study show that planting spearmint and large leaf mint can significantly repel D. melanogaster on raspberries and can be used as an important means for green prevention and control of raspberry orchards during fresh fruit picking， and white clover and alfalfa can be used as nectar plants and landscape plants complementing the orchard ecosystem. In addition， the repellent effect of spearmint on D. melanogaster in this study is similar to the repellent effect of mint on D. melanogaster studied by Zhong et al.[14]， which proves that peppermint plants have certain similarities in repelling D. melanogaster， and can serve as artificial grass species to be deeply explored. The repellent effects of white clover in the raspberry and blueberry orchards are quite different. The effect is better in the blueberry orchard， with a 15% difference in repelling effect， which may be because the fruiting period of raspberry is longer than that of blueberry， and the fruit matures in batches， providing a good living space and time for the reproduction of D. melanogaster. As people pay more attention to green orchards， sod culture will not only be one of the means to control weeds and reduce herbicides， but also take on the important mission of improving the orchard ecosystem， reducing fruit tree diseases and pests， and promoting fruit quality and efficiency. More grass varieties with high economic value and repellent effects on pests are worthy of further excavation and promotion.

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