Abstract:
A study was conducted at the College of Agriculture, Vellayani from
January 2001 to December 2001 to study the biology, species composition
and symptomatology of perianth infesting mealybugs, D. brevipes and P.
longispinus infesting the coconut palm and to assess the yield losses
caused by the pest and to evolve management measures.
The biology of the two species was studied after reanng them on
pumpkin fruits. The mean larval period and adult longevity of D. brevipes
and P. longispinus when reared on pumpkin were 36 and 103.3 and 26 and
57 days respectively. The mean sex ratio of D. brevipes was 3.17 and of
P. longispinus was 3.54. Pumpkin appeared to be a good host material for
mass rearing PMBs.
Studies on the yield loss assessment revealed an annual yield loss of
Rs 139.20/ palm in the highly susceptible palms whereas in the medium
and low susceptible palms the yield losses were Rs. 85.80/palm and Rs.
40.80/ palm respectively.
When the influence of bunch age on the extent of damage by
mealybugs was studied, highest mean per cent damage was observed in the
fifth bunch followed by fourth and sixth bunches. Maximum population
of PMBs were observed in the fifth nutlet. The mean population of D.
brevipes was maximum during May (1.31) whereas the mean population of
P. longispinus was maximum during March (1.13).
Studies on the susceptibility of stage of bunch to mealybug damage
indicated that the peak level of damage was in the fifth bunch.
Consequently the maximum damage was observed in the month of June.
Rainfall was observed to be the most important factor adversely affecting
mealybug population.
Development of symptoms as a consequence of feeding injury by
PMBs include drying of nut without drying of calyx, stunting, deformities
in the buttons such as development of cavities in place of embryo and
gummy exudation. The mean population of other perianth infesting
arthropods found associated with highly infested category of palms was
low when compared to medium and low category palms. A positive
relation between number of flowers per spikelet and susceptibility to
mealybugs was observed. A study on the reaction of nutlets of WC'T
variety to PMBs in terms of tepal colour revealed that orange and green
coloured tepals were the most preferred by PMBs. Ant species C. nuda,
T. albipis and A. longipes were seen closely associated with PMBs.
Among the various pesticides evaluated against PMBs, triazophos
(0.05) and profenofos (0.05) were found to be effective in controlling the
pest.
