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Biosystematic studies on the parasitoid Diaeretiella rapae (M’Intosh) (Hymenoptera: Braconidae) vis-a vis its aphid host

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Title Biosystematic studies on the parasitoid Diaeretiella rapae (M’Intosh) (Hymenoptera: Braconidae) vis-a vis its aphid host
 
Creator ACHINTYA PRAMANIK
 
Contributor Debjani Dey
 
Subject ---
 
Description T-8506
Aphids as pests are known worldwide. Their biological peculiarities along with
extensive monoculture and indiscriminate use of agricultural chemicals etc. have complicated
matters further which have in turn stimulated research on their biological control. Diaretiella
rapae (M’Intosh) (Hymenoptera: Braconidae: Aphidiinae) is the most common parasitoid
associated with various species of aphids in all the major agro ecosystems and has been
described as one of the most important factor for natural control of mustard aphid, Lipaphis
erysimi (Kaltenbach). Although very minute in size this parasitoid has been recorded from
many parts of our country. Considerable work on its hosts, seasonal occurrence and
parasitism have been carried out but a holistic approach involving emphasis on both
ecological and taxonomic studies has not been applied to this cosmopolitan species. Therefore
in depth studies were undertaken on D. rapae not only to quantify the morphological
variations present but also to study the inter and intra- plant distribution of D. rapae at field
level.
Forty quantitative characters including two meristic and thirty-eight ratio characters
from 167 specimens belong to 11 populations collected from nine different parts of India
along with 8 figures of the various diagnostic characters were used to redescribe D. rapae.
To validate the morphometric characters utilized in the present study, statistical
analyses were undertaken for evaluating the extent of variation within or among the
populations. Based on their CV values, sixteen characters were found to be essential for
discriminating different populations among which ratio of length of pronotum to length of
mesonotum was recorded with very high CV values and thus expected to contribute
significantly in differentiating the populations. Analyses of measurements showed that, three
ratio characters viz. length of flagellomere I to width of flagellomere I; width of mesopleuron
to length of mesosoma and length of M+Cu to length of 1Cua had heavier principal
component weights in the first principal component and served as the main contributing
variables in the diagnostic differentiation of the populations.
Following cluster analysis two groups were formed: Group I dominated by
populations from plains and Group II dominated by populations from higher altitude.
Populations of D. rapae reared from L. erysimi collected on cabbage in Aligarh and Delhi
appeared as the most closely related populations in the first group, with the population from
Pantnagar mustard joining as a sister group to the two while in the second group population
reared from L.erysimi on mustard from Nainital and cabbage from Pantnagar were placed as
the most closely related populations, with the population from Almora mustard joining as a
sister group to them. From our study it is hypothesized that being widely distributed in
different parts of India, with wide host range, formation of a host race as well as a
geographical race in D. rapae appears to be a remote possibility although some variability
may be observed between the populations of plains and higher altitude.
D. rapae has been recorded extensively by numerous researchers but its distribution
vis-a-vis its host L. erysimi, other parasitoids/ hyperparasitoids present in the field has not
been assessed. Since information about the distribution of both the pest and the parasitoid on
the plant helps identify a suitable sampling unit and a natural enemy threshold which may
lead to a rational aphid management in mustard field studies were conducted, during two
consecutive rabi seasons viz., 2009-10 and 2010-11, in order to assess the seasonal
occurrence and the spatial distribution of L. erysimi vis-a-vis its parasitoids/ hyperparasitoids.
Samples were collected at weekly intervals since the first colonization of mustard
plants by aphids (2nd standard week and 3rd standard week in 2010 and 2011 respectively) and
continued until the last harvest of plants (11th standard week and 12nd standard week in 2010
and 2011 respectively). During boththe years’ two parasitoids, viz., D. rapae and Aphidius
colemani Viereck, along with a hyperparasitoid Pachyneuron aphidis (Bouche)
(Pteromalidae: Hymenoptera) were recorded on L. erysimi on mustard (Brassica juncea
variety Pusa bold) at IARI. Generally, high L. erysimi densities were found during the second
fortnight of February for both years. The mummification rate showed a specific increasing
trend late in the season i.e. first half of March. In 2010, the percentage of mummification
reached 53.18 per cent at the end of the season whereas in 2011 it was as high as 65.5 per
cent. Although the density of L. erysimi individuals were higher on the terminal 10 cm twig of
the plants compared to those collected from the leaves in the middle and lower parts in both
years but statistically no significant difference was there. In contrast, the numbers of
mummified L. erysimi individuals were higher on leaves collected from the middle part of the
plants than on those from the top 10 cm twig and lower part during both the years. However
the relative abundance of A. colemani and D. rapae differed during the two years. Seasonal
abundance, hyperparasitic potential and distribution of P. aphidis, was also discussed.
The high densities of beneficials that are often reported to occur in mustard fields
clearly suggest that an integration of natural enemies into aphid management is feasible, and
these agents may play a key role in an Integrated Pest Management based strategy.
 
Date 2016-11-30T14:57:07Z
2016-11-30T14:57:07Z
2011
 
Type Thesis
 
Identifier http://krishikosh.egranth.ac.in/handle/1/88447
 
Format application/pdf
 
Publisher IARI, Division of Entomology