Some aspects of ecology and genetics of chironomidae (diptera) in rice field and the effect of selected herbicides on its population
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Date
2006-08
Authors
Ali Al-Shami, Salman Abdo
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Abstract
An ecological and molecular study was conducted on the aquatic insect
Chironomidae (Diptera) inhabiting the rice field in Bukit Merah Agricultural
Research Station (BMAES), Seberang Perai, Pulau Pinang Malaysia.
Investigation on the distribution and abundance of chironomid larvae
(Chironomidae: Diptera) showed that the larval population fluctuated following
the dynamic changes in rice field ecosystem. The maximum density in the first
season was 294.39 m·2 and 306.37 m·2 in the second season. Biweekly
sampling of larvae over two rice growing seasons of 2004/2005 revealed that
Chironomus kinesis was the most abundant species while four other species
Polypedilum trigonus, Tanytarsus formosanus, Tanypus punctipennis and
C/inotanypus sp were found in low numbers although they occurred during all
rice wet phases.
-2 The mean larval population was 120.95 larvae m and varied
significantly among sampling occasions and seasons (Kruskai-Wallis, X2=
174.29, df = 16, P= 0.000 and Mann-Whitney test = 19984, P = 0.000
respectively). More larvae were found in the plough phase in the absence of
rice plants in the field. The population was observed to increase approximately
two weeks after herbicide applications. Insecticides and fertilizers as well as the
onset of emergence of adults from larvae to adults probably accounted for
reduction of population numbers throughout the seasons. Four physicochemical
variables; water level, height of rice plants, conductivity of water and
nitrate-nitrogen weakly influenced the larval density (P < 0.05). The pH,
dissolved oxygen, temperature, total organic matter, total suspended solids and
phosphate showed no significant interaction with the population of chironomid
larvae in this rice field.
The effect of two herbicides 2,4-D Dimethylamine and Bensulfuron
methyl on the fourth instar larvae of Chironomus kiiensis was investigated.
Mortality of the larvae treated with 2,4-D Dimethylamine was observed after 24
h and the LC50 was 2638 mg ai L-1 which was a hundred times higher than the
normal applied dose of 0.753 mg ai L-1
• However, the direct toxicity of
Bensulfuron methyl was only observed after 72 h and the LC50 was 1.29 mg ai
L-1
. Three percent of the pupae successfully emerged to adult in the highest
concentration (500 mg ai L"1
) of Bensulfuron methyl compared with 60% in the
control. Thus 2,4-D Dimethylamine was a fast acting herbicide, killing the larvae
of C. kiiensis within 24 h. Bensulfuron. methyl was slow acting but it reduced
adult emergence, most larval individuals died during the pupal stage.
A preliminary study on the genetic relationship was conducted on C.
kiiensis, P. trigonus, T. formosanus, T. punctipennis and Clinotanypus sp based
on a 710 bp fragment of the mitochondrial cytochrome oxidase subunit I (COl)
gene. The Maximum Parsimony (MP) analysis produced a phylogenetic tree
which was in general agreement with the hypothesis based on morphological
traits. All members of each species form monophyletic groups. The
Chironomidae subfamilies form a sister taxon to the Tanypodinae with P.
trigonus as the basal group. The DNA method has proven useful in identifying
chironomid during certain life stages and offers a reliable and rapid approach for
routine identifications of ambiguous species or individu
Description
Keywords
Ecology and genetics , Chironomidae (diptera) , Selected herbicides