Res. Populo Ecol. (1967) IX, 113--129

THE ESTIMATION OF POPULATION DENSITY OF TItE GREEN

RICE LEAFHOPPER, N E P H O T E T T I X CINCTICEPS UHLER, IN

SPRING FIELD BY THE CAPTURE-RECAPTURE METHOD t

Kazuo NAKAMURA ~, Yosiaki IT6% Kazuyoshi MIYASHITA *

and Akira TAKAI ~

Division of Entomology, National Institute of Agricultural Sciences, Tokyo, Japan Ryugasaki Experimental Farm, Ibaraki Prefectural Agricultural Experimental Station,

Ryugasaki, Ibaraki Prefecture, Japan

INTRODUCTION

The green rice leafhopper, Nephotettix cincticeps UHLER, is an important insect

pest of the rice-plant in Japan which injures the rice-plant not only in direct way,

but also in carrying the rice dwarf virus. In the Kanto district, this insect hibernates

in the nymphal stage on gramineous weeds grown in resting paddy field and ridge,

and the adult emerges from late in March to mid-April. Three generations are

usually repeated throughout a year after it. To study on the population dynamics of

N. cincticeps, it is indispensable to know the number and other population parameters

of the hibernated generation adults in the resting paddy field, but this has not made

so far. It is mainly because of the difficulty of estimating the number of individuals;

direct counting of the insects on weeds is practically impossible, and the net-sweeping

presents only relative value when the sweeping efficiency is not known.

The capture-recapture method has been used in many insects, such as tsetse flies

(LLOYD, 1936; JACKSON, 1939), butterflies and moths (DOWDESWELL eta/ . , 1940;

FISHER and FORD, 1947), locusts and grasshoppers (RICHARDS and WALOFF, 1954;

DEMPSTER, 1957; IT6 et al., 1963), and lady beetles ([WAO et al., 1963), and it has

been shown that this method is superior to others to know the absolute number of

mobile insects. TAKAI et al. (1965) attempted to use the capture-recapture method

for N. cincticeps adults in the summer paddy field and showed that this method can

be applied to this insect.

The capture-recapture method is essentially based on two assumptions: that is,

the marked-and-released animals mingle completely with the unmarked ones and the

sampling efficiency is performed equally on the marked and unmarked animals.

When the mobility of insects is too small, as in the sunn pest (BARKS and BROWN,

1962), or the number of recapture is such small as the nil recaptures often occurs,

as in the blowfly (MACLEOD, 1958), difficulty is arisen in the application of this

method.

As the number of N. cincticeps in the hibernated generation is rather small and

1 Contribution from JIBP-PT No. 20.

114

the rate of recapture is also low, we need to develop a desirable design of the

release-and-recapture plan and the method of estimation of the population density.

This study was carried out in order to apply the capture-recapture method to

the adults of the hibenated generation of N. cincticeps and to estimate the number,

the birth- and death-rates of the adults.

METHOD

The experiments were carried out during the period from late in April to early

in May at Atsugi, Kanagawa Pref. in 1962, where the technique of marking, release

and recapture was first attempted to N. cincticeps adults to estimate population

parameters, and at Toride, Ibaraki Pref. from 1963 to 1965. The experimental fields

we used were the uncultivated paddy fields which stood round the cultivated paddy

fields. In April gramineous and other weeds grew thick all over the experimental

fields and the other areas were nearly bare land except the ridges and paths.

The mean dry weight of the weeds collected from 50cm • 50cm quadrats in the

fields No. 006 and No, 120 late in April, 1964 are shown in Table 1.

Table 1. The mean dry weights of the weeds collected from 50cm• quadrats in late April, 1964.

Experimental field 006 120

Alpecurus aequalis var. amurensis Cardamine flexuesa Stellaria Alsine var. undulata Astragalus sinicus The other species

16.7 g 11.3 g 1.9 0.9 1.5 5.0

0 2.9 0.3 3.7

Total 20.4 23.8

It is apparent from this table that the dominant species of the weeds in both

the fields is dent foxtail, Alpecurus aequaIis SOBOL. var. amurensis (LOMAR.), but

the flora of the field No. 006 is simpler than that of the field No. 120.

From early in May to mid-May, A. a. amurensis in the experimental fields died

gradually, contrary to the regeneration of weeds in the cultivated fields. In mid-May

the nursery beds of the rice seedlings were made in some paddy fields, and the

adults of leafhopper moved to the nursery beds.

The results of preliminary sampling with the sweep-net showed that no adult

was found at the ridges and paths, and a few in the cultivated fields, where a little

weeds grew.

Arrangement of the experimental fields at Toride are shown in Fig. 1. The

experimental plots were set up in these fields, and were divided into several quadrats,

as shown in Table 2 and Fig. 1. Sweeping was made with sweep.net on each quadrat

as to cover whole area by 20 strokes. The adults of N. cincticeps captured were

1962

(a t A t s u g i )

anaesthetized immediately with carbon dioxide gas in the polyethilene bag, and

marked with a small dot on the tegma using a fast-drying ink ('Pentel Pen'). The

number of marked females and males were recorded separately. Changing colours

and positions of the dot (on left or right tegmen), we can detect the date of release.

The marked adults were collected with an aspirator and released to the quadrat from

T a b l e 2. T h e out l ine of t he c a p t u r e - r e c a p t u r e se r ies for N. cincticeps adul t s .

Yea r Da te E x p e r i m e n t a l i Nos. of Size of plot Size of plot q u a d r a t q u a d r a t

23rd-25 th Apr i l

9 t h - l l t h M a y

2 6 t h - 2 9 t h Apr i l

1963

(at Tor ide)

105

211

" 1 0 i

504

1 8 m • 16m - - - -

18 • 16 - - - -

18 • 16 : - -

28 • 16 - - - -

006 20 • 10 1 0 m x 8m

120 20 x 4 0 8 10 •

1964 (a t Tor ide)

7 t h - 1 0 t h M a y

1965 (at Tor ide)

2 2 n d - 2 8 t h Apr i l

13 th -14 th M a y

20th Apr i l - 4 t h M a y

OO6 120

113

OO6

004

20 • 12 10 • 6 .7 20 • 8 10 • 10 • 5 10 • 5

20 X 7 3 . 3 22 - 1 0 X 6 . 7 - -

20 x 48 6 20 x 8

006 20 • 12 10 •

120 30 • 10 10 • --(lOx2o)

006

120

t , i , , 5 0 m

20 • 10 10 x 8

40 • 14 10 • ~(I0x29)

115

. . . . . . i . - _

/

h I . ,

304 0 0 6

Fig. 1. A r r a n g e m e n t of e x p e r i m e n t a l plots and q u a d r a t s in t h e p lo ts in 1963 a t Tor ide .

116

which they had been captured. We intended to scatter them over the quadrat as

evenly as possible.

The capture, marking and release were repeated in the same way on the

following days.

Some of the marked adults were brought to the laboratory and their mortailty

was compared with that of the unmarked ones, but no significant difference was

found between them.

DESIGN OF CAPTURE-RECAPTURE SERIES AND THE RESULT OF

THE PRELIMINARY CALCULATIONS

In 1962, a release-and-recapture was repeated two times on successive days.

The datum of this type aIlows us to apply the BAILEY's triple-catch method

(BAILEY, 1951).

Supposing that R, marked insects were released on the r th day, and the Ct

insects were captured on the tth day, in which the marked insects on the r th day,

Mtr, were included, the series in 1962 can be written as follows:

Days t = 1 2 3

No. of released insects r = l R1 [M21] [ M a ]

[No. of recaptures] 2 R~ [M3~]

No. of captures C1 Cz Ca

The number of adults was estimated by applying LINCOLN index, BAILEY'S

triple-catch method, LESLIE's three points method (LESLIE and CHITTY, 1951) and

method A grouping (LESLIE, 1952). The instantaneous birth- and death.rates (~ and x /

r, respectively) were calculated according to the triple-catch method. The results

are shown in Table 3.

Table 3. The number of AT. cincticeps adults in 1962, estimated by different

methods, and the instantaneous birth-rate (,S'~ and death-rate (~-), estimated

by BAILEY'S triple-catch method, with standard deviations.

Field 105 (April) 211 (April) 101 (May) 504 (May)

Number by Lincoln index Triple-catch m. Three points m. M. A grouping

Birth-rate Death-rate

16765• 6453•

10731• 16034• 1. 423• 436

--0.434• 122

13092• 9741•

12006• 16455•

--0.465• 484 --1. 251•

2144• 612& 121

1140~864 775~509

0. 786• 796 0. 110~1. 106

7065• 3840~ 2961

10304• 7728•

-0.069• -0.501• 1.088

The values of ~ and r were negative in many cases as shown in this table. This

is contradictory to the truth, for both the rates should not be essentially negative.

These negative values were caused probably by the higher recapture rate of M31 to

117

Ca than of M2L to C2. The greater variance of the number of individuals was

thought to be caused by the same reason. It suggests that the marked-and-released

adults did not mingle completely with the unmarked ones, at least by the next day

of the release.

In 1963, the mark-and-release was repeated two times and the capture was made

three times on the successive four days, that is:

Days t = 1 2 3 4

No. of released insects r : : l R~ [M21] [M31] [M41]

[No. of recaptures] ..... 2 . . . . . R2 ....... QM3~] ~M~2~_

No. of captures Ca C2 Ca C,

This series was repeated two (in the plot No. 120) or three (in No. 006) times,

but in the third series made in No.006 the number of captured insects was too

small to continue this series after the third day.

Supposing that the marked-and-released adults mingled completely with the

unmarked ones after the second day of the release, the number of insects on the v

second day, xe, is estimated by the BAILEy'S triple-catch method, the values of M3a,

M4t and M42 being used, as

"~ M41 (Ca + 1) R2 (1) x2= (M42+1) (M3a+l) "

Supposing a constant instantaneous birth-rate, fl throughout the experimental

period, the mean birth-rate between the nth and n + l t h days, b is written as

eq(n+l)__e3n b = : = e ~ - l . e ,~n

In the same way, the mean death-rate per day, d is written as d 1 - e - L

supposing a constant instantaneous rate, r. Then, the birth- and death-rates per day

is estimated by the BAILEY's equation, as

M~ (C4 -1-1) 1, (2) b = (M,~4-1) c~

R2 M41 d = 1- Rl(M~2+l) (3)

The result of calculation, however, revealed that the values of b and d were

negative in almost all cases. It may be caused not only by the incomplete mingling

of the released insects, but also by large sampling errors related to small recaptures.

In 1964, the release-and-recapture was repeated six times with the interval of

two or four days (see the table in appendix).

In 1965, the release-and-recapture was repeated two times with the interval of

two and four days. The density of the leafhopper was too low to capture sufficient

numbers for application of this method, so that the datum taken in this year was

used only for rough estimate of the number of individuals.

ESTIMATION OF DEATH-RATE

As mentioned in the preceding section, we cannot obtain the death-rate by the

118

BAILEY's triple-catch or other methods. According to NAKAGAKI (1963) who col-

lected N. cincticeps with the suction machines in the resting paddy field in early

spring, almost all the adults had emerged until mid-April in Chiba Pref., near

Ibaraki Pref. In fact, few nymphs were collected with sweep-net throughout this

work. The dilution due to new emergence of adults, therefore, can be neglected in

this study. As the area around the experimental field was regarded as the bare

land, the immigrated ones can be neglected too. Accordingly, the birth-rate during

this period may be regarded as zero.

If the death-rate would be estimated by some methods, therefore, the number of

insects could be calculated by the application of the FISHER's (1947) or MACLEOD's

(1958) procedure.

The est imation o f death-rate in 1963

Since three release-and-recapture series were repeated from late in April to mid-

May in the plot No. 006 in 1963 (see Table 2), the death-rates between series may

be obtain from the fluctuation of adults throughout this period.

When we estimate the number of insects according to LINCOLN index, supposing

no emergence and immigration (i.e., b=0), the number on the released day, x~, is

always obtained. According to LINCOLN index, the number of insect, x, is estimated

as x=R~C~/M~. Supposing that the death-rate, d, is constant, and denoting the

sampling efficiency on the tth day as f,, Ct and M,~ are written as follows,

respectively,

C,=f t (1 -d ) t -~x~ , Mt~=/ , (1 -d) t -~R~.

Then,

R~f, ( 1 - d ) *- ~x~. x = f t ( i _ d ) ~ : ~ R ; =x:. (4)

The number on the first day in each series, xl, therefore, can be estimated from

the captures and recaptures on the second, third and fourth day. But, we estimated

it from those on the fourth day, for the result of the preliminary calculations

suggested that the later from the released day the insect was collected, the more

homogeneous sampling was performed. If we denote the number on the r th day in

the sth series as x/ , the values of xP and x~ 2 are obtained as

x p = R I ( C 4 + I ) = 208• M41+1 10 = 1414.11,

46• xl~= ~2 =161.0.

As the recapture was made only one time in the third series, the value of x~ 3

obtained from the capture and recapture on the second day as

x, 3 = R~C2+1~=32.5 . M~I+I

There were eleven days between the first and second series, and six days between

1 According to BAILEY (1951), the equation for LINCOLN index was modified for small samples as this one.

119

the second and third series. If we suppose a constant death-rate per day between

the first and second series, dl and between the second and third series, d2, we can

write as follows:

(1 -all) llxll =x12, (5a)

(1 - d2) 6x12 = x~ 3. (5b)

Substituting the values of xl 1, x~ 2 and x~ 3 estimated above for those in these

equations, we obtained the values of death-rates as dl=. 179 and d2=.234.

As the birth-rate is supposed to be zero, the following equation is obtained,

substituting zero for b in the BAILEY'S equation (equation (2)).

Mat-- C3 (M~I+1) CA + 1 (6)

Substituting the actual value of M4~ in this equation, the value of M31 is obtained,

which means the number of insects that should be recaptured at homogeneous

sampling (express it as M3~).

The equation for the death-rate (equation (3)) is able to be written as

R2M41 M42 = - R l ( i L d ) - 1 . (7)

Substituting the actual value of M41 and the value of d obtained above for those

in this equation, the value of M42 is obtained, which means the number of insects

that should be recaptured at homogeneous sampling (express it as M42").

In this way, we obtained M31"=15.6 and M42"=22.2 in the first series and

M3t~=7.1 and M42~=0.7 in the second series. From these values of ~al~ and M,2 ~

and the actual value of M4~, the number of individuals on the second day was

obtained according to the equation (1) as x2~'=582.7 and x22'=114. 9.

The same procedure was repeated on the values of x~ v, x~ 2' and x~3;the new

death-rates obtained from the following equation, for there were elever days between

the second days in the first and second series, and five days between the second

and first days in the second and third series,

(1 - - d l ' ) l lx21' = x22', (1 - - d2") 5x22' = x13,

and the value of M42 ~' was obtained from these death-rates and the values of xa v'

and x22'' was obtained from the value of M42 ~'.

After this, the same procedure was repeated until the values of d~ and d2

approached to the certain values. The values of death-rates and the number of

individuals at each repetition were as follows:

repetition

X12 [ X22 [

dl d~

1 2 3 4

582.7 611.6 611.5 608.5 114.9 120.0 113.7 115.0 .1369 .1376 .1418 .1406 .1877 .2299 .2216 .2233

The calculation was stopped at the fourth repetition, where the fluctuation of

the numbers calculated was fixed, and the values of &=.141 and d2=.223 were

120

es t ima ted as dea th- ra tes .

In the plot No. 120, a r e l ease -and- recap tu re was repea ted two t imes . T h e plot

was set up in a pa r t of the t r i angu l a r field (see Fig. 1), so tha t the i m m i g r a t i o n

and emig ra t ion f rom or into the su r round ing par t of the plot m a y occur. Suppos ing

tha t the dea th . r a t e in No. 120 th roughou t the e x p e r i m e n t a l per iod was equiva len t to

dl in No.006 and tha t the emig ra t i on r a t e per day , e, was equal to the immig ra -

t ion ra te , i, and cons tan t t h roughou t the e xpe r ime n t a l period, we can wr i t e as

C,.=fi(1-dl)t-~x~ and M~,=f~(1-d~-e)t- 'R, . . When the n u m b e r of ind iv idua ls is

e s t ima ted accord ing to LINCOLN index, we obta in the fol lowing va lue ins tead of the

t rue number ,

RrC, (1 d~) ~-" x = M ~ - = ( i - 3 ~ e ) c-~x~' (8)

and this value in the s th ser ies is expressed as X / .

In the first ser ies X~ ~ was ca lcu la ted f rom the cap tu res and r ecap tu re s on the

four th day, as R1 (C4 +1) . (1 -- dl) 3

X ~ = M j , + I :~ (l::-di~e)a xL'=4152.5. (9)

In the second ser ies x~ z was ca lcu la ted f rom the da ta on the th i rd day because

of nil r e cap tu re on the four th day (M41), as

Xle= - R , ( C ~ + I ) . ( 1 - d l ) 2 M3~+1 ..... = ( l_d~__e)2 x J = 5 4 8 . 8 . (10)

As x~e--(1-d~)~xd (equation (5a)) , fo l lowing equat ion is obta ined, subs t i tu t ing

(1-&)~lx~ 1 for x, 2 in the equat ion (10):

1 (1 d, e ) 2 i l - d , ) ~~ x~ '=548.8. (11)

Solving the equat ions (9) and (11) s imul taneous ly , we obta ined e= .258 , x r

and x~=268 . 8.

Th i s means tha t . 258 of the adu l t s emig ra t ed and i m m i g r a t e d in the plot No. 120,

when the dea th - r a t e was . 141.

The estimation of death.rate in 1964

In 1964, a r e l ease -and- recap tu re was repea ted six t imes wi th the i n t a rva l of two

days (in only one occasion four days ) . But nil r ecap tu re s occur red too often to

obta in the dea th- ra te .

In the plot No. 006, the number s of ind iv idua ls on the second and fifth days , x2

and xs, respect ive ly , were ca lcula ted us ing the values of MT~ and M75 which showed

re l a t ive ly high recap tures , accord ing to LINCOLN index. W i t h repe t i t ion of the same

procedure to the one pe r fo rmed in 1963, we obta ined f inal ly as d=-.084, x 3 - 8 7 0 . 9

and x~=433.1.

In the process of calculat ion, the values of M~8" and MT~ ~, which were the

hypo the t i ca l r ecap tu re s a t homogeneous sampl ing , were obta ined f rom the values of

M72 and MT~, accord ing to the s imi la r equat ion to the equat ion (7), as

M , , ~§162 ... . . . . ~',(1 : ~ t ) t; - 1, (12)

121

where h means the number of days between the r th and r + l t h days (in this case,

t~=2). In the plot No. 120, the numbers on the second and third days, X~ and X3 were

calculated using the values of M72 and M73, which showed relatively high recaptures.

Supposing the same death-rate to the one in No. 006, in the same way in 1963, we

obtained as e=.022, x2=543.7 and x3=456.8.

Although there may be large errors in these estimation, it is apparent that the

death- and emigration-rates in 1964 were lower than those in 1963. The low death-

rate was caused presumably from the fact that the development of the leafhopper

delayed considerably in 1964, in relation to the low temperature. The less movement

in the field may be resulted from low activity, also related to the low temperature.

ESTIMATION OF NUMBER OF ADULTS

Number of adults

The number of adults in the plots No. 006 and No. 120 in 1963 and 1964 was

obtained in the previous section.

The number in the other plots in 1963 (No. 113 and No. 004) can be estimated

by means of FISHER and FORD's (1947) or MACLEoI)'s (1958) procedure, using the

death- and emigration-rates obtained in No. 006 and No. 120. The number in 1965

can be also estimated, using these rates in 1963.

As the total number of survived insects on the tth day which were released t - 1

before the tth day is Z (1--d-e)t-"R~ and the total number of recaptures on the r=l

t - 1 same day is Z Mtr, the number of adults on that day is possible to be estimated as

follows: t - 1

(C~+1) Z (1 -d-e ) t -~R, . X r = r = l t - : (13)

S M ~ + I r = l

The numbers estimated for these plots gives only rough values, for the homogeneous

sampling had not been assured.

The results are shown in Table 4 in the number of adults per lm 2.

Table 4. The number of N. cincticeps adults per lm ~ in each plot in 1963-1965.

Year 1963 '. 1964 1965

13th May - 2 4 t h Apr_ ........ 26th-Aprl ..... Date 27th Apr. ! 8th May X21 ..... _J _ _ X 2 2 . . . . . . XI 3 X3 . . . . . . . . . X2

ooG 0.761 I i 0.0 1 0.080 120 1. 79 [ 0.336 l 0 457 113 ! 0.639 i 004 : O. 038

122

From this table it is clear that the numbers of adults in the same season in

the three years were different greatly; that is, the number in 1963 was the highest

and that of 1965 was the lowest. They were also different among the plots in

certain years; that is, the numbers in No. 120 was higher than those in No. 006 in

1963 and 1965, whereas in 1964 the relation of them reversed. But, the densities of

adults late in April was always higher (more than 0.4 per lm 2) than those in May

in all the years and locations. The numbers decreased rapidly in May.

The estimation of the numbers of females and males

It is impossible to obtain desirable estimation of the number of females and

males, according to BAILEY's or other methods and also to the procedure used above,

because of low recapture rate of each sex, and then nil recaptures were often occurred,

especially during the later period. If we can know the rate of each sex to the

adults, however, the numbers of females and males can be calculated by multiplying

these rates to the number of adults. Assuming that the sampling efficiency was

not different between two sexes, the rates of each sex would be given from the rates

of them in the captures. The rate of females in captures in every day in 1963 and

1964 was shown in Fig. 2, and the average values of rate of females during each

period were calculated as shown in Table 5.

From these values, the number of males and females were estimated as shown

in Table 6. The number of males was higher than that of females during the early

period, but as the rate of females increased gradually, this relation reversed during

the later season. This fact agrees with the results of our direct observations in the

field.

~ 1 1 120

.5

1 9 6 4

J - 0 0 6

0 0 6

! �9 I ,b APR. MAY

Date

Fig. 2. Sex ratio of N. cincticeps adults in sweep-net captures in 1963 and 1964.

Table 5. The average rate of females to the adults captured during each period in 1963 and 1964.

123

Year 1963

Period 1st 2nd 3rd series series series

006 .42 .78 .80

120 .31 .58 - -

113 -- .71 - -

004 - - -- .90

1964

2nd to 4th to 3rd day 5th day

�9 3 4 ! . 4 8

�9 5 0 . 6 2

6th to 7th day

�9 4 8

. 7 1

i I

Year

Date

006 $

120 $

Table 6. The numbers of females and males of N. cincticeps in each plot in 1963 and 1964.

1963 1964

27th Apr. X21

8th May X2 2

89.7

25.3

133.9

97.0

13th May Xi a

26.0

6.5

255.6

352.3

379.1

843.7

22nd Apr. X~

352.9

685.1

271.9

271.9

28th Apr. i 4th May X4 ~7

294.3 174.4

318.8 189.0

199.4 134.8

122.0 51.1

F r o m these numbers of males and females, the death-ra te of each sex was

calculated as g iven in Tab le 7.

Table 7. The death-rate of females and males during each period in 1963 and 1964.

Year

Period

006

120

Between the 1st and 2nd series

�9 091

�9

�9 090

�9 171

1963

Between the 2nd and 3rd series

�9 192

�9 238

1964

Between the 2nd and 4th days

Between the 4th and 7th days

�9 030 .084

.226 �9

�9 050 .063

.221 �9

SAMPLING EFFICIENCY

As the insects were captured wi th a sweep-net , the sampl ing efficiency is expected

to vary, depending upon the m a n y factors�9 Since the number of captured insects is

expressed as Ct =fixt , the sampl ing efficiency on the t th day, f t can be obtained f rom

f t = CJx t .

The resul t of calculat ion of the sampl ing efficiency in each plot was listed in

Tab le 8 wt ih a tmospher ic t empera tu re , wind direction, the force of wind wi th

BEAUFORD's scale and wea the r at 9 a .m. , at Ryugasaki , about 6kin east f rom Tor ide .

Since the w o r k was a lways begun at about 10 a .m . in No.006 and ceased by noon,

the wea the r condit ion in this table did no reflected exac t ly the wea the r in the

124

w o r k i n g t ime . Bu t i t m a y no t be so g r e a t l y d i f fe ren t , e spec ia l ly in No. 006.

Table 8. The sampling efficiency with sweep-net and the weather condition at 9 a.m. on each day at Ryugasaki, 6km east from the working area, in 1963-1965.

Year

Date

006

120

113

004

Atmospheric temperature

Wind direction

The force of wind*

Weather

1963

27th 28th 29th Apr. Apr. Apr.

f2' f3 ~ f , '

.386 .203 .149

.208 .169 .121

15.6 13.5 14.9

- - E E

0 1 2

fine cloudy fine

8th 9th lOth May May May fz2 f2 f42

13th 14th May May

�9 530 .280 .087 .646 .395

�9 342 .242 .082

.300 .219 .070 t �9 333 .286 !

19.0 19.0 13.6 19.7 22.0

- - N E E S W

0 2 1 3

rain fine

0

cloudy cloudy cloudy

Year

Date

006

120

Atmospheric Temperature

Wind Direction

The force of wind

Weather

24th 28th Apr. Apr. f+ A

�9 109 �9

.088 .151

16.8 12.2 16.0 21.3 16.0

N E E - - E

2 3 2 0 1

fine cloudy fine

1964 1965

30th 2nd 4th 26th 28th Apr. May May Apr. Apr.

f5 f~ fr f2 _ f3 . . . . .

.097 .106 .292

.028 .070 �9

* The force of wind with BEAUFORD'S scale�9

�9 281 .072

�9 178 .046

13.3 9.6

0 0

cloudy cloudy cloudy cloudy

F r o m t h e t ab le it is c l ea r t h a t t h e s a m p l i n g eff ic iency v a r i e d f r o m .03 to .65;

t h e r e a r e d i f fe rences a m o n g t h e d a y s and plots�9 T h e d i f fe rence a m o n g p lo ts in t he

s a m e day , h o w e v e r , is no t so g r e a t as t h e one a m o n g days . T h i s f ac t s u g g e s t s t h a t

t h e f luc tua t ion of s a m p l i n g eff iciency, fo r t he m o s t par t , d e p e n d s u p o n t h e w e a t h e r

condi t ion �9

W h e n the s a m p l i n g eff ic iency w a s p lo t t ed a g a i n s t t h e t e m p e r a t u r e and the fo r ce

of wind , and the s a m e i n t e n s i t y po in t s of ef f ic iency w e r e jo ined w i t h l ines, as s h o w n

in Fig . 3, i t w a s s h o w n a p p a r e n t l y t h a t t h e eff ic iency v a r i e d g r e a t l y in r e l a t i on to

t h e s e t w o f ac to r s . In gene ra l , t h e l o w e r t h e t e m p e r a t u r e is a n d t h e g r e a t e r t h e

fo rce of w i n d is, t h e l o w e r t h e s a m p l i n g eff ic iency is.

125

3

O

0

�9 05 ,4.0/

'04 f / 0 " 4 0

/ o/ 0 _ _ �9 _ . . .___~_--r / /

/ / . / C / / . / /

�9 I . I I I I I * I I J I I

1 0 15 2 0 "C

Temperature

Fig. 3. Relationship of the sampling efficiency with sweep-net to the atmospheric temperature and the force of wind with BEAUFORD'S scale in the plot No. 006. The figures show the sampling efficiency of the points or the lines which are joined among the same intensity points of efficiency.

DISCUSSION

The capture-recapture method was previously used by TAKAI et al. (1965) on

N. cincticeps of late summer generation, but the difference of sampling efficiency

between the marked and unmarked insects was not seen in their work. The differ-

ence between the sampling efficiency of marked and unmarked insects which were

found in this work seems to be caused by incomplete mingling of the released

insects, of which activity was considered to be very low, related to the low temper-

ature in early spring. In the plot No. 006 in 1963, for an instance, the expected

numbers which should be recaptured at the homogeneous sampling were calculated

as M31"=15.6 and M42~==21.2 in the first series and M31" 7.1 and M42"--0.7 in the

second series, whereas the actual recaptures were M31-8 and M42-9 in the first

series and M3~=7 and M42=0 in the second series. Obviously, the difference between

the expected and actual recaptures is large in the first series, but in the second series

it was small. This fact shows that the sampling efficiency in the second series is

considered to be nearly same between the marked and unmarked insects, and

suggests that almost all marked insects mingled with the unmarked ones, because

the temperature in the second series was so high as to cause high activity of

insects.

In case of this work, where the sampling efficiency differes between the marked

and unmarked insects, it is impossible to apply the equations proposed by many

authors, but if the sampling efficiency of each insect or the birth- and death-rates

126

of population are known, we can estimate the number of insects, according to the

equation (13). In these two parameters the latter may be obtained more easily,

for instance, from the laboratory rearing.

The estimation using the pooled recaptures of the females and males and of the

different released days are generally very effective when the recaptures are low.

But, as pointed out by MACLEOD (1958), if the sampling efficiency are different

between the females and males, and/or among the released days, the number of

insects estimated is not precise. In Fig. 2, where the rate of female to the adults

captures was shown, the rate of females was below 0.5 during early period.

Assuming that the sex-ratio of the leafhopper is 0 . 5 : 0 . 5 , it suggests that the

sampling efficiency of females was lower than males during this period, since the

almost all adults had emerged by this time. The estimated number of insects (and

then, also death-rate) seems, therefore, to be rather over-estimated during early

period.

In 1963, the death-rate per day was estimated as dl==. 141 (between the first and

second series) and d2=.223 (between the second and the third series). Supposing

that the adults emerged on the first day in the first series and that the death-rate

of these adults after the third series was equal to d2, the mean longevity of adults is

calculated as 32.6 days. Similarly, the mean longevities of females and males in

the plot No. 006 were obtained as 56.6 and 16.5 days, respectively. SAMESHIMA

and NAGAI (1962) collected the N. cincticeps adults of the hibernated generation from

the field and reared them with dent foxtail, Alpecurus aequalis amurensis in a

cylinder set out outdoors. From their datum the mean longevity of the adults was

calculated as more than 30 days. In this case, the true longevity will be longer than

this value which is the longevity f rom the collected date. ESAKI and HASHIMOTO

(1931, 1932) reared N. cir~cticeps indoors under the natural temperature and obtained

the mean longevity of the hibernated adults as 40.6 in female and 28.9 days in

males in 1930 and 38.3 in female and 24.7 days in males in I931. Compared the

values obtained in this work with these values, the longevity of adults shows com-

paratively good agreement, but the one of each sex did not show it, especially being

longer in females. This was resulted presumably from the lower sampling efficiency

of female during early period compared with male, as shown above. Since the

number of females estimated by multiplying the number of adults with the rate of

females, the number and the death.rate of females were considered to be underesti-

mated during early period. From these reasons the longevity calculated would be

longer than true. Contrary to this, the death-rate of males would be estimated

greater and then, the longevity would be shorter.

The sampling efficiency was dependent upon the weather condition, especially

on the temperature and the force of wind. It seems that the temperature and the

force of wind affect activity of the leafhopper. The force of wind may significantly

affect the difficulty of strokes of the sweep-net. The efficiency occasionally exceeded

127

�9 5 in May. This is probably caused not only from the high temperature, but from

the decrease of difficulty of strokes of the sweep-net in the simple flora, resulted

from the death of dent foxtail.

The sampling efficiency with sweep-net greatly varies with many factors, so that

the study on tbe relation of these factors to the efficiency must be made in future.

When the map showing the relation of weather and flora conditions to the sampling

efficiency is made from such a study, it will be possible to estimate the number of

leaf hoppers in the hibernated generation with the simple sweeping�9

SUMMARY

The population parameters of green rice leafhopper, Nephotettix cfnctic@s in

hibernated generation was estimated by the capture-recapture method on the grami-

neous weeds of resting paddy field from late in April to mid-May, 1962-1965.

The difficulty of applying the capture-recapture method to this insect is caused

from the low density and the low activity of the leaf hopper, so that it is necessary

to make the suitable plan of capture-recapture series and to construct the special

method to detect the population parameters.

The number of adults differed greatly among the years and among the plots in

the same year. But, in general, the density was relatively high late in April, and

decreased rapidly in May. The number of males was higher than that of females

late in April, but decreased rapidly to become lower in May.

The sampling efficiency with sweep-net depends upon the many factors, such as

weather and floristic conditions; especially the atmospheric temperature and the

force of wind are considered to affect greatly to the efficiency. In general, low

temperature and strong wind are the cause of low sampling efficiency.

APPENDIX

Table 1. The numbers of releases (Rr), captures (C~) and recaptures (Mtr) in the plots of No. 006 and No. 120 in 1963.

26th 27th 28th 29th 7th 8th 9th 10th lgth 14th Date Apr. Apr. Apr. Apr. May May May May May May

No. 006

t= i 2 3 4 i 2 3 4 I 2 j . . . . . . . . . . : . . . . . . . . . . . . . . .

Rr r= l 110 [19] [8] [9] 46 [5] [7] [1] 21 [2] [Mtr] 2 233 [6] [7] 61 [5] [0] : 10

Ct 110 235 106 67 46 61 25 6 21 10

No. 120

t = ! 1 2 3 4 i 1 2 3 4 l i

I

Rr r= l I 151 [4] [3] [3] I 56 [5] [4] [0] L L

[Mtr] 2 i 254 [11] [5] I 79 [7] [2]

Ct ] 151 254 177 109 56 79 48 14

128

Table 2. The numbers of releases (Rr), captures (Ct) and recaptures (iW~r) in the plots of No.006 and No. 120 in 1964.

Date

No. 006

20th 22nd 24th 28th 30th 2nd 4th Apr. Apr. Apr. Apr. Apr. May May

. . . . . i . . . . . . . . .

t = i 1

Rr r = l 15

2

2 3 4 5

79 <3> <1~ <0~

(Mtr~ 3 i 4

5

6

Ct 15

95 <I~ (2)

22 <0)

44

6 7

No. 120

t =

R~ r = l

2

<Mtr~ 3 4

5

6

Ct I _

34

1 2

<03 <1> <2> <5)

46 (0~

79 95 22 50 46 106

(3) 48

3 4 5 6 7

(8> (0~ <1> <2> <53

64 <3) ~2) <4) 69~

9 (1) <03 (13 19 <1~ <1)

36 (0~

34 48 69 9 19 36 90

ACKNOWLEDGEMENTS: We wish to express our t hanks to Mr. H. MUTOH, Toride, Ibaraki Pref.,

who lent us his fields in which this work was carried out. T h a n k s are also due to Dr. S. TAKAK1

and Dr. S. NAsu, Division of Entomology, National Ins t i tu te of Agricul tural Sciences, for useful

advice in th is work.

REFERENCES

BAILEY, N.T.J. (1951) On estimating the size of mobile populations from recapture data.

Biometrika 38: 293-306.

BANKS, C.J. and E. S. BROWN (1962) A comparison of methods of es t imat ing population density of

adul t sunn pest, Eurygaster integriceps Pu'~. (Hemiptera: Scutelleridae) in wheat fields. Ent.

exp. & appl. 5: 225-260.

D~MPSTER, J. P. (1957) The population dynamics of the Moroccan locust (Dociostaurus maroccanus

TaUNBERO) in Cyprus. Anti-Locust Bull. 27: 1-60.

DOWD~SWELL, W.H., R.A. FISHER and E. B. FORD (1940) The quant i ta t ive s tudy of populations iu

the Lepidoptera. 1. Polyommatus icarus Roa-r. Ann. Eug. 10: 123-136.

ESaKL T. and S. HasmMoTo (1931) Report on the leaf-hoppers injurious to the rice plant and

the i r na tu ra l enemies. No. 2. Dept. Agric., Kyushu Imp. Univ., Publication no. 2, 25,III: 1-57.

Esa~, T. and S. HasmMo.m (1932) ditto, No. 3. Ibid. no. 3. 25.III: 1-42.

FlSaER, R.A. and E.B. FORD (1947) The spread of the gene in na tura l conditions in the colony

of the moth Panaxia dominula L. Heredity 1: 143-174.

ITS, Y., A. TAKAI, K, MiYasm,r:~ and K. N*KAMUR* (1963) Es t imat ion of density, survival ra te and

129

dilution ra te of Mecostethus magister (Or thoptera : Acrididae) populations by the mark and

recapture method. Res. Popul. Ecol. 5: 51-61.

IwAo, S., K. M~zuTa, H. NAgAMURA, T. OI)A and u SATo (1963) Studies on a na tu ra l population of

the large 28-spotted lady beetle, Epilaehna vigintioctomaculata Mm.~nvLsKr. I. Prel iminary

analysis of the overwintered adult population by means of the marking-and-recapture method.

Jap. J. Ecol. 13: 109-117.

JaogsoN, C.H.N. (1939) The analysis of an animal population. J. Anim. Ecol. 8:234-246.

L~sLIE, P.H. (1952) The es t imat ion of population pa ramete r s f rom data obtained by means of

the capture- recapture method. II. The es t imat ion of to ta l numbers . Biometrika 39: 363-388.

L ~ s ~ , P.H. and D. C n n ~ (1951) The es t imat ion of population pa ramete r s from data obtained

by means of the capture- recapture method. I. The maximum-likelihood equations for es t imat ing

the death-rate . Biometrika 38: 269-292.

L~o~ , Lm (1936) Assessment of a tsetse population. Bull. ent. Res. 27: 261-267.

MaoLeon, J. (1958) The es t imat ion of numbers of mobile insects from low-incidence recapture

data. Trans. R. Ent. Soc. Lond. 110 : 363-392.

NAKA~AKI, S. (1963) Overwinter ing of green rice leafhopper, Nephotettix bipunctatus cincticeps

U u t ~ . Proc. Kanto Pl. Prot. Soc. 10: 43.

RmuARns, O.W. and N. WALo~- (1954) Studies on the biology and population dynamics of Bri t i sh

grasshoppers . Anti-Locust Bull. 17: 1-182.

S:~a~SnIMA, T. and K. 1N-A~aI (1962) Relation between the life-history of green rice leafhopper,

Nephotettix cincticeps Un=e~, and rice yellow dwarf propagation. Japanese Jour. Appl. Ent.

Zool. 6 : 267-273.

TA~AL A., Y. I'r& K. NaKA~wA and K.M~yAsnI'rA (1965) Es t imat ion of population density of the

green rice leaf-hopper (Nephotettix cincticeps Un~v.~) by the mark- recapture and the sweeping

methods. Japanese Jour. Appl. Ent. Zool. 9: 5-12.

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.@ 7 - r :/~~ @ ~ ~,',C~YE. L,f:~

~, lc .~ { t ; .o t:0