Effect of feeding by Metadelphaxpropinqua (Fieber)(Homoptera, Delphacidae) on barley

Raatikainen, M., Raatikainen, T. & Vasarainen, A. 1994. Effect of feeding by Metadelphax propinqua (Fieber) (Homoptera, Delphacidae) on barley. Agricultural Science Finland 3: 513-517. (University of Jyväskylä, Department of Biological and Environmental Science, P, O. Box 35, FIN-40351 Jyväskylä, Finland and Agricultural Research Centre ofFinland, Institute ofPlant Protection, FIN-3 1600 Jokioinen, Finland.)


Introduction
In 1969-1970 we investigated cereal diseases transmitted or caused by aphids and leafhoppers in Turkey.Our interest focused on the biology of Metadelphax propinqua (Fieber) (Homoptera, Del- phacidae), also (Raatikainen and Vasarainen  1990), a planthopper widely distributed in the Palaearctic and Nearctic region (Metcalf 1943).According to Dlabola (1957), it is also common in Turkey.We were primarily concerned with the damage it does to barley.

Material and methods
We started with an investigation of the ecology of M. propinqua at Bornova in western Turkey and continued with trials at Tikkurila in Finland.The planthoppers were collected from a field at Bornova.The tests were conducted from September 1971 to March 1972 in a glasshouse at a temperature of 20-25°C.The test plant was bar- ley (cultivar Tammi).The plants were sown in 43 x 25 x 12-cm wooden boxes lined with polyethylene film.The bottoms of the boxes were perforated to allow drainage.Seeds of test plants were sown in six parallel rows, four seeds to each row, at equal distances from one another and at a depth of 3 cm.During test feeding periods each planthopper was caged with one seed- ling under a cylinder of PVC plate, 3 cm in di- ameter and 25 cm tall; the upper end was covered with gauze.There were also two ventilation openings near the bottom.Control plants were caged in the same manner.
The number of planthoppers on one plant in the rearing box was 0,1, 2 or 4 and the length of the feeding period was 4, 8 or 16 days.The trials were made with nymphs, males and females.The The plant properties measured are listed in Tables 1-3.The statistical method used was analysis of variance, and statistical significance is indicated by asterisks as follows: *** = P < 0.001, ** = P <O.Ol and * = P < 0.05.

Results
The number of M. propinqua nymphs and the length of their feeding period (time of stay) on barley did not have any major effect on the plant properties measured (Table 1).The most important change occurred in the dry weight of the plants, which decreased significantly due to the effect of both the number of nymphs and the length of their feeding period.The combined ef- feet of the number of nymphs and the length of their feeding period on the length of barley plants was significant 22 days after sowing.The number of nymphs lowered the grain weight of whole plants and the 1000-grain weight of the main shoot almost significantly.M. propinqua males had a more marked effect on the properties of barley than did the nymphs (Table 2).The greater the number of males and the longer the time that had passed since feeding, the less the barley grew in length.Further, the greater the number of males on a plant, and the longer the feeding period, the more the weight of the plant decreased.Feeding led to a decrease in the number and weight of grains of the whole plant and secondary shoots.
The effect ofM. propinqua females on the properties of barley was much greater than that of either males or nymphs (Table 3).The number of females and the length of their feeding period usually lowered very significantly or significantly the length and weight of plants, the number of grains, the grain yield and the 1000-grain weight.The effect on growth was most striking at the end of the feeding period, but thereafter the plant seeded and gradually recovered.

Discussion
Our earlier studies (Bremer and Raatikainen  1975) indicated that the planthopper individuals we investigated did not transmit viruses.M. propinqua is a small planthopper that dam- 2.9 2.9 ages a plant in two ways.It draws nourishment out of the plant and simultaneously injects into it saliva which helps to digest the food and injurious to the plant.The combined effect of these measures is less with nymphs than with adults, and with male than with female adults.This may be due to the fact that females start laying eggs approximately 1-5 days after emergence and the number of eggs is greater than that of other planthoppers studied (Raatikainen and Vasarainen  1990).Females thus need more food than males and so cause more injury to the plant than either males or nymphs.
There is great variation in the abundance of M.
propinqua and, from time to time, it may cause a significant decrease in the yield of grasses.

Table 1 .
Effect of feeding by Metadelphax propinqua nymphs on barley.
test plants were six days old at the beginning of the trials.The length of the day was 16-19 h.

Table 2 .
Effect of feeding by Meladelphax propinqua males on barley.

Table 3 .
Effect of feeding by Metadelphax propinqua females on barley.