BIOECOLOGY AND ECONOMIC INJURY LEVELS (EIL) OF Dysdercus volkeri F (HETEROPTERA: PYRRHOCORIDAE) ON SUNFLOWER (Helianthus annuus L.) IN SAMARU ZARIA, NIGERIA.
BIOECOLOGY AND ECONOMIC INJURY LEVELS (EIL) OF Dysdercus volkeri F (HETEROPTERA: PYRRHOCORIDAE) ON SUNFLOWER (Helianthus annuus L.) IN SAMARU ZARIA, NIGERIA.
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Date
2013-01
Authors
MANI, Ubaidu
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Abstract
Field and laboratory studies were conducted on the bioecology and economic injury
levels (EIL) of Dysdercus volkeri Fab. (Pyrrhocoridae: Heteroptera) on sunflower in
Samaru Nigeria. The objectives of the studies were to determine the biology of D.
volkeri, susceptible stage of sunflower for damage by D. volkeri, the economic injury
levels of D. volkeri, the influence of weather factors on D. volkeri and to screen different
accessions of sunflower for resistance to D. volkeri damage. The result of the studies
indicated that growth stages R7 (when the back of the head has started to turn a pale
yellow colour), R8 (when the back of the head is yellow but the bracts remain green) and
R9 (when the bracts become yellow and brown and the stage is regarded as physiological
maturity) took about 10, 14, 14 days respectively. The result of the biological studies
showed a marked difference between the life cycle of D. volkeri in the field and that in
the laboratory. Eggs laid by adult in the laboratory took three days to hatch compared to
3-14 days in the field. D. volkeri appeared on sunflower at R7 growth stage in both 2008
and 2009. Nymphs started appearing at R8 growth stage in both years. A total of 28--42
days was required from egg laying to adult emergence in the field compared to 24-28
days in the laboratory. There was significant difference (P= 0.05) regarding the number
of insects and the damaged seeds on the nine accessions of sunflower tested. On mortality
and longevity, there was also a significant difference between treatments. Predators of D.
volkeri were observed including the phytophagous Pyrrhocorid, Odontopus sexpunctatus
L. that had not been reported attacking D. volkeri before. The result also showed that the
number of predators was not commensurate with the number of D. volkeri to warrant
effective control. The D. volkeri sex ratio indicated that it was 1:1 male-female and the
best criterion for sex determination was the size based method. The result showed R8 as
most susceptible and 2-3 insects/head of sunflower crop constituted the economic injury
level. The gain threshold was 1254 kg/ha and 1255 kg/ha in 2008 and 2009 respectively.
Accessions PI 298632, Funtua, Ames 3236 and PI 176974 showed resistance to D.
volkeri damage. On lipid value, the result indicated significant difference among the
treatments. Accessions Ames 3236, PI 176974, PI 193775 and Funtua recorded the
highest lipid value. Similarly, the accession that recorded the highest fatty acid value was
Ames 1838 with 0.97mg/100ml. On yield, the result showed significant difference P <
0.05 among accessions. Funtua and PI 298632 appeared to have the highest yield of 1240
and 1239 kg/ha respectively.
Description
B.Sc. AGRIC. (UDUS) 1995, M.Sc. CROP PROTECTION (ABU), 2004
A DISSERTATION SUBMITTED TO THE SCHOOL OF POST
GRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA IN
PARTIAL FULFILMENT FOR THE AWARD OF DOCTOR OF
PHILOSOPHY IN CROP PROTECTION
DEPARTMENT OF CROP PROTECTION
FACULTY OF AGRICULTURE,
AHMADU BELLO UNIVERSITY ZARIA
JANUARY, 2013
Keywords
BIOECOLOGY,, ECONOMIC,, INJURY,, LEVELS,, EIL,, Dysdercus,, volkeri,, HETEROPTERA,, PYRRHOCORIDAE,, SUNFLOWER,, Helianthus,, annuus,, SAMARU,, ZARIA,, NIGERIA