A STUDY ON EGG DEVELOPMENT AND SURVIVAL IN LOCUSTA MIGRATORIA MIGRATORIOIDES (Reiche and Fairmaire) IN THE CHAD BASIN AREA
A STUDY ON EGG DEVELOPMENT AND SURVIVAL IN LOCUSTA MIGRATORIA MIGRATORIOIDES (Reiche and Fairmaire) IN THE CHAD BASIN AREA
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Date
1986-10
Authors
ACKONOR, JOSEPH B.
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Abstract
Field and laboratory studies on egg development,
survival and hatchling weight in L. migratoria migratorioides
were made at Ngala (12°20'N, 14°10'E) and
Maiduguri (11°53'N; 13°16'E) in the Lake Chad Basin locust
outbreak area.
During 1981 to 1985 data on eggpods were compiled
for four seasons namely, the rainy season (July to
September); the harmattan (mid-November to February); the
hot-dry season (March to mid-May) and the early rains
season (mid-May to June),
In the field locusts were bred in open-bottomed
wooden frame cages in three soil habitats classified as
sandy, sandy-clay loam and clayey.
In the laboratory breeding occurred in cages provided
with predetermined soil/water mixtures for oviposition;
incubation temperature ranged from 22 ± 1°C to 40° ±1°C.
The laboratory study centred on the age of the female in
relation to fecundity and the effects of moisture —
including flood and drought—and also of temperature, on
egg development, survival and hatchling weight,
A total of 907 eggpods were obtained in the field
during the rainy season; these comprised 350 in sand,
298 in clay and 259 in sandy-clay loam. During the
harmattan 49 eggpods were obtained, 24 in clay, 16 in sand
and nine in sandy-clay loam soils. During the hot-dry
season 35 eggpods were obtained; 16 of these occurred in
clay, 11 in sand and eight in sandy-clay loam. Sixteen
eggpods were obtained for the early rains seasons, eight
in clay, seven in sand and one in sandy-clay loam.
Egg development rate was inferred from incubation
period; it was fastest in the early rainy season when the
mean incubation period in sand was 9.5 days and corresponded
to the highest mean air temperature ranging from 29.8 C to
36.2 C. Development rate was slowest during the harmattan;
incubation averaged 24 days in clay and coincided with the
lowest mean air temperature ranging from 19.2°C to 25.6°C.
Average development rates for the rainy season were intermediate
to those for the seasons mentioned above; the
rates coincided with the intermediate air temperature
ranging from 24.6°C to 27.3°C;incubation lasted 13.6 days
in sand, 16,0 days in sandy-clay loam and 18.1 days in
the clayey soil.
Egg survival rate was inferred from the percentage
of eggpods that hatched in a given eggpod population. The
best survival rates were recorded during the rainy
season when 49.9% of 350 eggpods survived in sand, 25.1$
of 298 eggpods survived in clay and 16.6% of 259 eggpods
survived in sandy-clay loam. During the harmattan 11.4$
of 24 eggpods survived in the clayey habitat only and
during the early rains 29.2$ of seven eggpods survived in
the sandy habitat only; eggs did not survive in any habitat
during the hot-dry season.
Egg mortality factors under field conditions were
identified as predation, parasitism, desiccation and
decay. These factors were seasonally influenced. Predation
was the major mortality factor, particularly during
the rainy season; the major predatory suspects were larvae
of coleoptera while a mite of the genus Allothrombium was
a minor predatory agent. The parasites comprised Scelio
africanus Remaudiere, S. sudanensis Remaudiere which
belong to the family Scelionidae (Hymenoptera) and an
unidentified worm of the family Enchytraeidae. The two
parasitic groups caused minor mortality in the rainy
season only. Desiccation and decay, which were prevalent
during the drier and wetter seasons respectively, caused
little mortality.
Laboratory observations showed that the female
locust laid a maximum of five eggpods, the mean being
2.9. The number of eggs per eggpod declined with the
age of the female but development and survival rates,
and also hatchling weight, were independent of parental
age.
Laboratory observations also indicated that development
rate was influenced by soil moisture, including flood
and desiccation; wetter soil conditions and drought
retarded egg development. Development rate was also
influenced by temperature, 34 ±1°C being the optimum at
which the average incubation period was 10 days.
Eggs survived at temperatures ranging from 22 ± 1°C
to 38° ± 1°C; no egg survived at 40 ± 1 °C. Survival was
higher in wetter soils but flood was detrimental. Older
eggs survived better in flood but pharates about to hatch
were highly susceptible. Drought was also detrimental to
survival.
Hatchlings emerging from wetter soils were heavier
and had higher survival potentials
Description
A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR
OF PHILOSOPHY TO THE AHMADU BELLO
UNIVERSITY, ZARIA
NIGERIA
OCTOBER, 1986.
Keywords
EGG DEVELOPMENT,, LOCUSTA,, MIGRATORIA MIGRATORIOIDES,, (Reiche and Fairmaire),, CHAD BASIN AREA