http://www.paper.edu.cn THE NATURAL CONTROL ABILITY OF PARASITIC CHALCIDS ON POPLAR SCALES QUADRASPIDIOTUS GIGAS (THIEM ET GERNECK) AND EFFECT OF ARTIFICIAL MIGRATION

Hu Yinyue Chi Defu Shao Jingwen Zhang Fengbin Li Chengde

Northeast Forestry University Province 150040

E-mail [email protected]

Abstract: This paper reported the investigation of the population complex of parasitic natural enemies on the main stem pests, Quadraspidiotus gigas (Thiem et Gerneck), Lepidosephes saliciana (Borchs.) and Pulvinaria salicicola (Borchs.), in protective poplar forests of Northeast China, a total of 12 species of parasitic chatcids being discovered.

The species of parasitic chalcids, discovered on poplar scales were evaluated and screened using indexes of outstanding natural enemies: ecological compatibility, temporal synchronization, density responsiveness, reproductive potential, searching capacity, dispersal capacity, Spatial distribution pattern, resistance to unfavorable conditions and food requirements. Investigations discovered that Pteroptrix longiclava (Giraut) and Encarsia gigas (Tshumakova) highly synchronized with the host Q. gigas in ecological compatibility, period of growth and spatial distribution pattern, possessing high reproductive, searching and dispersal capacities, in positive density-dependent relationship in population dynamics with that of the host. The food requirement of adults of the two species was easy to satisfy. Adults were easy to preserve, with definite resistance to rain and wind.

In 1992 and 1993, parasitic chalcids were artificially migrated and released in experimental forests hundreds hm2. Surveys in 1993, 1994 and 1995 showed that chalcid safely colonized these forests, average parasitic rates reaching 20.8%, 30.7% and 28.5% respectively. After two years of releasing, chalcid dispersed away for more than 30m. In the paper, the dispersal model of chalcids was also formulated.

Keywords: Quadraspidiotus gigas, Pleroptrix longiclava, natural control ability, artificial migration - 1 - http://www.paper.edu.cn

INTRODUCTION In poplar protective forests of Northeast China, Pests, seriously damaging stems of poplar, are Quadraspidiotus gigas (Theim and Gerneck), Lepidosaphes salicina (Borchs.) and pulvinaria salicicola (Borchs.)

Q. gigas is a typical pest caused by human activity. The distribution of this insect was already recorded, but no serious damage caused by this pest was recorded. In recent tens of years, since plantation of pure poplar forests in large areas in north China, with the addition of application of large amounts of organic phosphate, organic chloride, amino format and pseudopyrethrin insecticides in pest controlling of trees and crops, causing the serious destruction of original ecological environment, the control system of the poplar scale lost its stability, resulting in serious outbreaks in North China. On the basis of this analysis, we adopted artificial migration and enhance measures in order to effectively control populations of the poplar scales.

On the introduction of natural enemies, though discussions about the superiority of single species or multiple species introduction, effectiveness of introduction of monophagous or polyphagous natural enemies, are still underway, most biocontrollers all agree that the beneficial insects, introduced to control target pests must possess following characters: cecological compatibility, dtemporal synchronization, edensity responsiveness, freproductive potential, gsearching capacity, hdispersal capacity, ispatial distribution pattern, jresistance to unfavorable conditions, kfood requirements and habits.

Three indexes are used for the final evaluation of the efficiency of utilization of natural enemies: ccolonization of the natural enemy in new habitats, only when the insect was discovered in the successive years after releasing, and maintained a definite population level, this insect may be said to safely colonized. dThe natural enemy rapidly disperse in the region of introduction. eThe population of the pest decreased obviously after the introduction of the natural enemy, and a population equilibrium inadequate to cause any damage may be reached in a rather short period.

The main natural enemies used for the biological control of poplar scales in our country and other countries are parasitic chalcids, lady beetles and mites, and a number of successful evidences were gained in the past. The research group evaluated and screened species of parasitic chalcids discovered on the poplar scales, using the above mentioned nine indexes of outstanding natural enemies. Recognized to be the outstanding parasitic chalcids, Pleroptrix longiclava and Encarsia gigas were selected for artificial migration experiments. After migration, colonization, dispersal and population dynamics of the natural enemies and the host were evaluated.

METHODS

- 2 - http://www.paper.edu.cn Evaluation of the control ability of parasitic chalcids on the poplar scales Study on the ecological compatibility and reproduction of the parasitic chalcid. For five years, members of the research group investigated on large areas of the main plantation region of poplar in liaoning, Jilin and Heilongjiang provinces. From three species of poplar scales: Q. gigas, L. salicina and P. salisicola, 12 species of parasitic scales were collected. denitrified to be: (1)E. gigas (Tshumakova), host Q. gigas (2)P. longiclava, (Girault), host Q. gigas, (3)Marietta cranesi (howard), host Q.gigas, (4)Comperiella bifasciata (Howard), host L. salicina (5)Aphytis quadraspidioti Li, host Q. gigas, (6)A. proclia (Walker), host L. salicina, (7)A. vandenboschi Debach et Rosen, host L. salicina, (8)Coccophagus psendopulvinariae Li, host Salisicola, (9)C. scutellaris (Dolman), host P. salicicola, (10)Metaphycus pulvinariae (Howard), host P. salicicola, (11)Metaphycus sp., host Q. gigas, (12)Eucyritus sasakii Ishii, host P. salicicola. The generation, period of adult prosperity, reproductive capacity and longevity of adults and distribution were listed in table 1.

Table 1. The comparsion of generation, peak of adult emerge time, reproductive ability and longevity of different chalcids Chalcid spp. generation overwinter female kinds of adult mean eggs distribution per year period adult reproductive female laid/per emerge logevity female time P. longiclava 1 generation larva last ten bisexaul 44-52h 200-310 Jilin,Liaoning, days of June M. carnexi 1 generation larva middle bisexaul 48-96h 50 Jilin,Liaoning, or of 2 generation June Q. gigas 2 generation larva first ten bisexaul 14-56h 18-50 Jilin,Liaoning, days of June A.quadraspidio- 1 generation larva egg first bisexaul and 4-5d 26-56 Haliun, ti or ten day parthenogenes 2 generation of June

C. bifasciata 1 generation egg first ten mainly 48h 160 ,, or day of parthenogene- Zhaodong 2 generation June sis

Data on their distribution in table 1 showed that P. longiclava, E. gigas and M. carnesi all distribute over the main area of outbreak of Q. gigas: Jilin. Liaoning, Harbin, Suihua, Hailun, Zhaoyuan, Zhaodong, much wider than that of other chalcids. There are reasons to believe that the ecological compatibility between these three species and poplar scale host is better than other two species.

Considering the reproductive potential, P. longiclava has one generation per year, with a mean egg

- 3 - http://www.paper.edu.cn amount of 260, 310 eggs for highest, much higher than the mean egg amount of 30-50 for Q. gigas. E. gigas has two generations per year, the mean egg amount being 38, 50 for the highest, also much higher than these of Q. gigas.

Investigation of the parasitic rate in the wild indicated that E. gigas was the dominant parasitic species on Q. gigas in the protective forest of Xinhua County, Suihua City. Heilongjiang, during 80s, the parasitic rate reaching as high as 43.8-80.9%. Due to the constant application of chemical insecticides in poplar pest control, investigation in 1992-1993 discovered that the population of this species was almost eliminated. P. longiclava was the dominant species of chalcids in Hailun County, Heilongjiang. Investigation in the protective forest of Lunhe town of this county revealed that the parasitic rate of chaicids on Q. gigas reached 45.6%, Q. gigas occupying 64% of the total parasitic rate, M. carnesi, 34.0%, Surveys in Sanjing Town, Suihua City during 1992-1994 discovered that parasitic rates of Q. gigas were 75.2%, 29.4% and 52.2% respectively, due to the disuse of insecticide for a long time.

The above analyses of ecological compatibility, reproductive potential and natural parasitism showed that Q. longiclava and E. gigas are natural enemies of better quantity.

Temporal synchronization of chalcids and their hosts In Heilongjiang, poplar scales live one generation in a year, females emerge in the middle of May, reaching the peak in the last ten days of May, the last ten days of June is the period of abundance of fixed nymph of the first instar, therefore, the optimal insect form for parasitism of most of chalcids appear at the end of June and the beginning of July. Table 1 showed that the peak periods of egg laying in the two generations of Q. gigas temporally synchronized with the peak period of the optimal insect form for parasitism. The emergence of adults of the over-wintering generation occurred at the beginning of the last ten days of May, exactly for them to meet new adults of Q. longiclava. Parasitism was sure to be successful, if only one chalcid larva lived in the host. Q. longiclava over-wintered in the form of newly hatched larvae in the body of second instar nymphae of female hosts. Abundant periods of emergence and egg laying appeared in the last ten days of June and the first ten days of July. Eggs were laid into the body of fixed nymphae of the second instar of the host. progress of the emergence of chalcids was in synchronization with the development of the first instar fixed nymphae of the host, the reason of rather high natural control capacity of chalcids over poplar scales.

Density responsiveness relationship between Q. longiclava and the host population In order to determine the interaction between population densities of chalcids and their hosts, data were collected in protective forests in Sanjing Town, Suihua city and Shuanglongshan Town, , in May, 1993. In the survey, damaged trees were divided into four classes according to the density of the host, each class was, in turn, divided into five groups, and 5-7 trees were sampled in each group. Samples were collected from the upper, middle and lower parts of the stem, and from north, east, south and west directions, altogether 1344 samples.

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Data of host insect density and parasitic rates of chalcids were evaluated using Richards’ formuta: B Y=A×[1-EXP(-Kx)] , where A=74.3187565, B=1.85539, K=0.1669862, R=0.893521, therefore 1.8553 Y=74.3187565×[1-EXP(-0.2669862x)] (Fig 1). The parasitic rate of chalcids per unit area increased with the increase in population density of the host, their population density being positively correlated. Especially, when the density of host insect was at a low level, the parasitic rate of chalcids increased obviously with the increase of density of host insects. This evidence demonstrated the high searching capability of chalcids on poplar scales. Fig 1 indicated that when the population density of the host reached 10-39/2cm2, density (parasitic rate) of chalcids became stable. This formula may be used to predict the parasitic rate of chalcids.

Degree of Synchronization of the spatial distribution of the parasitic complex and the host Synchronization of the spatial distribution of chalcids, mainly P. longiclava and E. gigas, and the host was also an important index for evaluation of the control capacity of chalcids. The spatial distribution pattern of chalcids and their host was calculated using frequency x2 test and several index method of degree of aggregation on the basis of large amount of sampling, being determined to be of aggregation distribution. The basic form of distribution appeared to be that of negative binomial, the main component was population of individuals and the population formed the aggregation dispersal. The closeness of the height of distribution between chalcids and their host was one of natural reasons of high parasitic rate and control ability of chalcids.

Resistance capacity of chalcids to wind and rain Resistance capacity of chalcids to wind was experimented with a blower. Results were listed in

- 5 - http://www.paper.edu.cn table 2. Table 2 showed that wind under 4 grade gave no influence to chalcids. When wind was stronger, chalcids remained motionless. Records of wind speed in June over the years in Suihua City demonstrated that the average speed did not exceed 5.5m/s. Therefore, under normal conditions, influence of the natural wind on the control capacity of these two chalcid species was not great. Rain was simulated by a sprayer. Chalcids remained motionless under artificial rain, moved slowly or still motionless after, with the body standing erect and the head raised.

Table 2 Influence of wind on adult chalcids wind velocity (m/n) 2.8 3 4.2 5.5 6 8 9.2 10 10.8 wind power scat 2 2 3 4 4 5 5 5 6 repeats 3 3 3 3 3 4 4 4 5 Number blown 0 0 0 0 1 1 2 4 3

Dispersal capacity of chalcids The dispersal capacity of chalcids was studied at the same time with the artificial migration. Results indicated that in two years, chalcids dispersed away for 25-30m, a rather high capacity of dispersal.

Host-searching capacity of chalcids Study in this item was reported in the paper actual “The influence of kairomone of Q. gigas and the ovipositoin deterring pheromone on the control ability of parastitic chalcids”

Influence of food, temperature and light on survival and viability of chalcids Results of artificial feeding demonstrated that adults of P. longiclava and E. gigas showed an high taxis toward 20% sugar or 20% honey solution and feeding on these food may enhance their viability. These two species also showed taxis toward water, white no taxis toward water, while no taxis toward de-shelled live scales. Therefore, 20% sugar or honey solution may be used as food in the adult stage, in order to enhance the host-searching and controlling ability. Feeding on 20% sugar or honey solution may also extend the longevity of E. gigas for 3 and 2.3 folds and increase the amount of eggs for 63% and 50%. Feeding on 20% sugar solution may increase the longevity of P. longiciava for 2.5 fold and egg amount for 20%, while no significant effect of honey was observed. It was suggested to use 20%, sugar solution as supplementary nutrition in adult stage for enhance their control capacity over poplar scales. Darkness and low temperature may extend the longevity of chalcids for 2.5-3 days, and darkness in 4℃ refrigerator, for 4-5 days, but preservation of chalcids in refrigerator for longer time may decrease the viability and egg amount of chalcids. It is better to preserve chalcids in refrigerator no longer than 3 days.

Analysis of the effect of artificial migration In order to increase the parasitic rate of chalcids on poplar scales, selection of areas and trees of chalcid source, predictive report of developmental progress, determination of chalcid release amount and technique were studied, and the effect of artificial migration was observed and

- 6 - http://www.paper.edu.cn analyzed. Survey of the effect of chalcid release on the migration ground After the release of chalcids in 1992 and 1993, the parasitic rate was investigated by counting the new emergence holes of chalcids. Though no new release in 1994, the survey in 1995 demonstrated that chalcids already established stable population on the experimental areas. Data was listed in table 3. Table 3 Parasitic rate after releasing year 1993 1994 1995 no of trees 10 36 10 rate(%) 28.8 30.7 28.5

Table 4 Dispersal distance and parasitic rate distance from the point of release 0 5 10 15 20 25 30 average parasitic rate % 53.3 32.5 29.5 23.6 22.8 22.7 5.4 average parasitic rate of the forest % 30.7

Two years after releasing of chalcids, in June, 1994, dispersal capacity of chalcids was surveyed on large areas in Hongji Forest Farm, City. Chalcids were sampled at distances 5m, 10m, 15m, 20m, 25m and 30m from the point of releasing and in all four directions: North, East, South and West, and average parasitic rate were calculated. Chalcids already dispersed as far as 30m. The average parasitic rate of the dispersed area reached 27.2% and the host population was weakened greatly.

Fitting of the dispersal model of the two dominant chalcid species after artificial migration In the study of the relation between insect density and dispersal distance, following model was used to fit: N=a+blnx+(c/x), where N was number of insects maked, x was the distance for the marked point of releasing, a, b and c were constants. Using data in Table 4, the above equation was calculated with the method of minimum squares, resulting N=32.5830-5.3757lnx+61.4766/x, multiple correlation R=0.8217479, estimated standard error=0.3247308. Good result of simulation indicated that this equation was fit to describe the dispersal of chalcids (Fig. 2).

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Analysis of poplar scale population and parsitizing chalcids after migration In July, the experiment forest of a 1000 hm2 and the surrounding forests were surveyed for parasitic rate of chalcids. Under the united control of red stabbed ladybeetle, the insect density of poplar scales reduced to only 0.17/cm2-2.78/cm2, 0.55/cm2 in average, so poplar trees in Hongji Forest Farm, attacked by poplar scales, were all classified to be 0 grade (Table 5).

Table 5 Average parasitic rate of chalcids on poplar scales in Hongji Forest Farm No of plots 3-2a 2-2b 3-3 4 2-2 3-3 62-a average rate in the parasitic rate% 19.52 28.37 23.83 26.66 14.26 14.50 22.73 Experimental forest average rate% 22.6 28.5

For 3 years, parasitic rate in the experimental forest and surrounding forests were very similar and steady, all in the range of 20-30%.

CONCLUSIONS

(1)P. longiclava (Giraut) and E. gigas (Tshumakova) were evaluated to be the outstanding natural enemies among those 12 species of parasitic chalcids, using the 9 outstanding natural enemy evaluating indexes such as the ecological compatibility. (2)After two years of artificial migration and releasing of those two species of outstanding parasitoids in the experimental forest, the average parasitic rate reached 20% to 30% in the experimental forest stands and the surrounding stands in Hongqi Forest Farm.

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