PhD

Family Coccinellidae, the lady beetles, belong to the superfamily
Coccinelloidea of the order Coleoptera and comprises approximately 6000
described species worldwide. Tribes Scymnini and Stethorini of the subfamily
Scymninae of Coccinellidae are economically important predators successfully
used in the biological control programmes of sucking pests of crops. Members of
Scymnini are mainly predators of aphids, mealybugs, whiteflies and scales, whereas
Stethorini are specific to mites. Though the fauna of Scymnini and Stethorini in
India is species rich, it is poorly studied.
The present investigation on “Systematics of the tribes Scymnini and
Stethorini (Coleoptera: Coccinellidae) from south India” was carried out during
2015-17. The objectives include the following: (1) taxonomy of the tribes Scymnini
and Stethorini associated with sucking pests in different agricultural ecosystems of
south India, (2) prepare a key to the species of Scymnini and Stethorini and (3)
generate DNA barcode for different species of Stethorini.
Purposive surveys were undertaken across different districts of Kerala,
Karnataka and Tamil Nadu covering 47 locations and 64 crops under different
agricultural ecosystems. Beetles and immature stages of Scymnini and Stethorini
were collected along with the associated prey. Immature stages of Scymnini and
Stethorini were reared to adults. The specimens were then mounted, labeled and
preserved as per standard procedures. The beetles were dissected and the taxonomic
characters viz., antenna, mouth parts, prosternum, tarsus, post coxal line, male and
female genitalia were studied and illustrated. The specimens were identified up to
species level. Descriptions, illustrations and key to genera and species of Scymnini
and Stethorini of southern India were prepared.
The study encompasses 28 species of Scymnini of which six are putative
new species. Two species are recorded for the first time in India and two species
each from south India and Kerala are new records.
Scymnini
include
Axinoscymnus,
The genera treated under
Cryptolaemus,
Horniolus,
Nephus,
Sasajiscymnus and Scymnus. The genus Scymnus, represented by 20 species, of
which 18 species are placed in three subgenera viz., Scymnus, Neopullus and Pullus.
Two species are treated separately, as these differ distinctly from the known
subgenera. The genus Nephus is represented by three species, Axinoscymnus with
two species and Cryptolaemus, Horniolus and Sasajiscymnus with one species
each.
Stethorini are represented by 10 species in two genera: Stethorus and
Parastethorus. Two putative new species of the tribe are described. Six species of
Stethorini are new reports for Kerala. Two subgenera recognized under the genus
Stethorus are Stethorus and Allostethorus. represented by four species each.
Stethorus keralicus, one of the most common species, has been treated separately
in this study, as its characters are not in agreement with the known subgenera. The
genus Parastethorus is represented by only one species.
The prey ranges of Scymnini and Stethorini were documented. Species
distribution map were prepared for the species studied. Twenty one species of prey
in four families viz., Aphididae, Pseudococcidae, Aleyrodidae and Diaspididae
were recorded in association with the tribe Scymnini. Two new prey records for
Scymnini are Toxoptera odinae for Scymnus pyrocheilus and Saccharicoccus
sacchari for Nephus tagiapatus. Among Scymnini, Scymnus coccivora and S.
saciformis are widely distributed with wider host range of six species as prey, while
species of Axinoscymnus, though widely distributed, is specific to whiteflies.
Among Stethorini, Stethorus pauperculus was found to be the predominant species
with wider host range, while Stethorus keralicus was specific to Raoiella indica.
New prey records for Stethorini includes Tetranychus okinawanus and T. truncatus
for Stethorus forficatus; T. macfarlanei for S. pauperculus and Eutetranychus
orientalis for Parastethorus indira.
For barcoding the species of Stethorini, DNA was isolated using Qiagen
DNeasy blood and tissue kit and the COI locus was amplified and sequenced. The
sequences were aligned and characteristic barcode gaps were identified for
Parastethorus indira, Stethorus forficatus, S. pauperculus, S. rani, S. keralicus, S.
(Allostethorus) sp. 1 and S. (Stethorus) sp.1. Pairwise distances between the
sequences were analysed which showed that intraspecific divergence ranged
between 0.00 to 0.03, while the interspecific distance ranged between 0.14 to 0.24.
A phylogenetic tree was constructed with 21 sequences in MEGA 7 using the
maximum likelihood tree method. The sequences were submitted to GenBank
(NCBI) and to BOLD for the generation of species specific barcodes.
The study identified 38 species of predatory coccinellids in the tribe
Scymnini and Stethorini in association with aphids, mealybugs, whiteflies, scales
and mites, which are serious pests of crops. Knowledge on the taxonomy of these
predators and their prey range throws light on the potential of the above groups in
biocontrol of sucking pests.