MSc

Mealybugs (Homoptera: Pseudococcidae) are oval, soft bodied insects causing
severe damage to plants not only by sucking the sap but also as vectors of viral diseases of
crop plants. The mealybugs infesting roots of crop plants are termed as subterranean
mealybugs or root mealybugs. Honeydew excreted by mealybugs attracts ants, and in turn
they provide protection to mealybugs from their natural enemies and also help in
transportation to other fields. Recently, root mealybug infestation was reported from
different localities of Kerala. However, studies on diversity of root mealybug - ant
association and seasonal incidence were scanty. Hence the present study, ‘Diversity of root
mealybugs of Kerala’ had been carried out to identify the root mealybugs and associated
ant species and to study the seasonal incidence, host range and geographical distribution of
major root mealybugs.
Purposive sampling surveys were carried out at different districts of Kerala covering
30 locations and 11 host plants. The root mealybugs and associated ants were collected
separately in vials with 90 per cent ethanol. The specimens were labeled with sample codes
and preserved as per standard protocols.
The study revealed the presence of eight species of root mealybugs belonging to
five genera viz., Formicococcus Takahashi, Planococcus Ferris , Dysmicoccus Ferris,
Antonina Signoret and Xenococcus Silvestri. Maximum diversity was found in the genus
Formicococcus, representing three species viz., Formicococcus polysperes Williams,
Formicococcus lingnani Ferris and Formicococcus mangiferacola Williams. The genus
Planococcus was represented by Planococcus lilacinus and Planococcus sp. The genus
Dysmicoccus, Antonina and Xenococcus were represented viz., Dysmicoccus brevipes
Cockerell, Antonina graminis Maskell and Xenococcus annandalei Silvestri, respectively.
Three species viz., F. lingnani, F.mangiferacola and A. graminis were recorded for the first
time from Kerala.
The root mealybug, F.polysperes was recorded to be having wider host range and
was found infesting black pepper, banana, avocado and goat weed. Pineapple mealybug,
D. brevipes was recorded on pineapple and nut grass, while Planococcus sp. was reported
on durian and black pepper. Root mealybugs, F. lingnani, F. mangiferacola, A. graminis,
P. lilacinus and X. annandalei were recorded from single host plant each viz., nut grass,
mango, paragrass, coffee and cardamom respectively.
The morphological identification of ants associated with root mealybugs revealed
seven species of ants of which maximum number of ant species were associated with root
mealybug, F. polysperes. The ants associated with F. polysperes were Nylandria indica
Forel, Tapionoma indicum Forel, Myrmicaria brunnea Saunders, W.W. and
Crematogaster rogenhoferi Mayr . The ant associated with F. lingnani was N. indica; while
Carebara affinis Emery with D. brevipes and Paratrechina longicornis Latreille with
Planococcus sp. on pepper. Ant seen in association with the subterranean mealybug, X.
annandalei was Acropyga acutiventris Roger. Among the ant species, N. indica was found
to be the major species associated with Formicococcus from Kasaragod, Kannur, and
Wayanad districts.
The major root mealybug species, F. polysperes was, noted from seven locations
of three districts viz., Kasaragod, Kannur and Wayanad respectively. The root mealybugs,
F. lingnani, F. mangiferacola, A. graminis, P. lilacinus and Planococcus sp were reported
from Wayanad whereas D. brevipes was recorded from Wayanad and Thrissur districts.
Molecular characterization of root mealybugs and ants was performed by
isolation of genomic DNA and amplification of mitochondrial cytochrome oxidase one
(mtCO1) locus using specific primers. The sequencing of polymerase chain reaction (PCR)
product and in- silico analysis of eight species of mealybugs and one species of ant was
carried out. The sequence data of the following four root mealybugs viz., F. mangiferacola,
F. lingnani, A. graminis and X. annandalei were absent in the NCBI data base. The
sequences of these mealybugs were deposited in the NCBI database for the first time.
Remaining four species of mealybugs showed 91-100 per cent similarity and were in
agreement with the morphological identification. The sequences were submitted to NCBIGenbank
for future access and use. The sequences were also uploaded to Barcode of Life
Data systems (BOLD) and generated barcodes for eight species of mealybugs and one
species of ant.
The study on seasonal incidence of root mealybug F. polysperes showed that the
population of mealybugs increased during rainy season from June and reached its peak in
the month of September when the rains subside. The population was least during the
summer months. Correlation of mealybug population with weather parameters indicated a
significant negative correlation with maximum soil temperature and significant positive
correlation with relative humidity and number of rainy days.