192
N. WALOFF
‘We numborn of flitting moth8 Rtodily inarsllsed in the evenings, attaining a peak hetween 6 pm and 8 pm, and the time of dispersal flights
outside the breeding site (Area 4) closely followed this daily rhythm.
Agwu assessed both the “flitting” flight and dispersal by means of the
suction traps, broom trap plants and with sticky traps (Broadbent
et el. 1948) and by direct observations. Within the plantation most
of the flight waa concentrated between 3-5 ft above ground level.
Dispersive flights laated eight weeks in 1965 and the numbers of moths
captured fell off with the distance from the plantation. A linear relationship between the logarithm of the number of moths (y) and the
logarithm of the distance from the breeding site (x) could be described
by the regression equation, where y = 2.7577-0-5705 x (p < 0-001).
Leucoptera emerge with one third of their eggs already mature. The
relative number of mature eggs to that of the egg rudiments, the state
of the fat body of the females, the number of spermatophores in the
bursa copulatrix and the presence of corpora lutea were used to aeseas
the age of the dispersing population, Dissections of the females colleofed
on the trap plants established that although the emigrating moths are
mature, most of them are young and some virgin. The females emigrating in the later part of the flight period are older, fertilised and have
all oviposited.
Agwu considers that the dispersive movements in Leucoptern are
truly migratory at the beginning of the flight period but later become
extensions of trivial movements.
The effects of various factors on daily numbers of moths emigrating
were subjected to the multiple regression analysis. The seven variables
computed were the age of the population, the size of the population, the
number caught per day, temperature between 18.00 h and 21.00 h, the
mean daily temperature, sunshine between 15.00 h and 21.00 h and the
amount of r&infall. The size and the age of the population as well as the
temperature at the daily peak hours of flight were the most important
factors, whereas rainfall was the most important variable in inhibiting
flight; 79% of the variability could be explained by the seven variables
used in the computation.
The numbers that emigrated throughout the s m o n were estimated
Ijy Waloff and Bakker’s method (1963), and only a very slight increase
in emigration was noted when the population waa extremely dense in
1963 (me Table LVIII). Thue almost the same proportion of the population emigrates irrespective of the population size and this still further
aupports Johnson’s concept that migration is an inherent activity.
The most convincing demonstration that the process of emigration
may be affected by density in some species emerged from Watmough’s
work on the broom Psyllidae and one of the main changes in adult
N. WALOFF
‘We numborn of flitting moth8 Rtodily inarsllsed in the evenings, attaining a peak hetween 6 pm and 8 pm, and the time of dispersal flights
outside the breeding site (Area 4) closely followed this daily rhythm.
Agwu assessed both the “flitting” flight and dispersal by means of the
suction traps, broom trap plants and with sticky traps (Broadbent
et el. 1948) and by direct observations. Within the plantation most
of the flight waa concentrated between 3-5 ft above ground level.
Dispersive flights laated eight weeks in 1965 and the numbers of moths
captured fell off with the distance from the plantation. A linear relationship between the logarithm of the number of moths (y) and the
logarithm of the distance from the breeding site (x) could be described
by the regression equation, where y = 2.7577-0-5705 x (p < 0-001).
Leucoptera emerge with one third of their eggs already mature. The
relative number of mature eggs to that of the egg rudiments, the state
of the fat body of the females, the number of spermatophores in the
bursa copulatrix and the presence of corpora lutea were used to aeseas
the age of the dispersing population, Dissections of the females colleofed
on the trap plants established that although the emigrating moths are
mature, most of them are young and some virgin. The females emigrating in the later part of the flight period are older, fertilised and have
all oviposited.
Agwu considers that the dispersive movements in Leucoptern are
truly migratory at the beginning of the flight period but later become
extensions of trivial movements.
The effects of various factors on daily numbers of moths emigrating
were subjected to the multiple regression analysis. The seven variables
computed were the age of the population, the size of the population, the
number caught per day, temperature between 18.00 h and 21.00 h, the
mean daily temperature, sunshine between 15.00 h and 21.00 h and the
amount of r&infall. The size and the age of the population as well as the
temperature at the daily peak hours of flight were the most important
factors, whereas rainfall was the most important variable in inhibiting
flight; 79% of the variability could be explained by the seven variables
used in the computation.
The numbers that emigrated throughout the s m o n were estimated
Ijy Waloff and Bakker’s method (1963), and only a very slight increase
in emigration was noted when the population waa extremely dense in
1963 (me Table LVIII). Thue almost the same proportion of the population emigrates irrespective of the population size and this still further
aupports Johnson’s concept that migration is an inherent activity.
The most convincing demonstration that the process of emigration
may be affected by density in some species emerged from Watmough’s
work on the broom Psyllidae and one of the main changes in adult