Study on the Development of Sorghum Chafer (Paclllloda Illterrupta (Oliver) (Coleoptera: Scarabaeidae) Under Different Physical and Edaphic Factors
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Date
2002-12
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Addis Ababa University
Abstract
A laboratory study supported with field observations was done on the life cycle, the effect of
physical' and edaphic factors on the development of Pachlloda illlel'l'upla (Oliver) (
Coleoptera: Scarabaeidae). The food preference and factors contributing to extended diapause
of the adult were also included in the study. The laboratory study was conducted at four
different temperature regimes (20, 25, 30 and 35°C) and four soil moisture levels (9, 17, 23
and 29%). Soils collected from Afar, Tikur-Inchini, Guder River near Ambo were used
separately and mixed with different propOliion of cow-dung to note its effect on laral
development. Based on the information obtained fi'om fanners in the infested area eight types
of food substances were tested for their effect as bait. In the life cycle study (at 25°C & Moisture 17%) the average oviposition rate was fOllnd to be
0.58 eggsl day/ female. Whitish soft shelled eggs were laid separately in soil varying (strata)
from 3-18 cm. in depth. The mean number of incubation days of egg was 9.63±1.4 ranging
between 8 and 13. Larval development took an average of 59.09 ± 1.94 days ranging between
42-73. Body length was constantly increasing till around 52 days where it reached 30.2 m111
and was shrinking latter and measured 28mm at about the 70th day. Larval head capsule
width, however showed discontinuolls; but constant increase and at an average 3.14±0.0Imm
was measured in final days (62-70). Pupal development ranged fi'om 18-30 days with an
average of24.47 ±3.5 days. The depth of pupation site was found to be dependent on moisture
level. When soil moisture is less the larvae went down deep in to the soil to pupate and when
it is high, they remained in the upper layers. Soil temperature however did not show
significant effect on pupation depth. The adults required an average of 93.79± 1.8 days,
ranging from 68-116 to emerge. The laboratory study and the field observation confirmed that P. interl'llpta are univoltine insects but the adults have two phases (emerging seasons). The
first phase emerges directly from pupa, and it is non reproductive and worst pest of crops such
as sorghum and maize and enters in to the soil for diapausing for about nearly 8 months. The
stable temperature in the soil especially under tree shades, food reserve p31iicularly fat
contributes for long lasting diapause. This emerges as second phase synchronized with rains
and flowering of non crop plants such as Acacia spp., and this is the reproductive phase.
Beetles of this phase feed mainly on flowers, mate, lay egg in the soil and die The presence of cow-dung in the soil was found necessary for completion of the life cycle.
The cow dung serves the larvae as food. and essential for growth, however when its
concentration increased exponentially, the growth rate decreased, but the total life cycle
shortened. Soil moisture and temperature have also shown significant effects on percentage
survival and developmental rate. Moisture levels of 17 and 23%were found to be more
important as compared with moisture regimes beyond and below these. Temperature of 25
and 30°C were found to be very essential for survival of larvae and for the completion of life
cycle. Among the eight food substances tested as bait, ripe banana was most preferred
followed by ripe guava. Residues of local beer, 'tej' and 'katicala', roasted maize and
sorghum flour were preferred next while non-roasted sorghum flour was the least preferred.
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Biology