PhD.

A study on ‘Bio-ecology and management of borer pests infesting yard long
bean, Vigna unguiculata subsp. sesquipedalis (L.) Verdc.’ was conducted at the College
of Agriculture, Vellayani during 2014-17. The main objective was to study the biology
and population dynamics of borer pest complex infesting yard long bean, Vigna
unguiculata subsp. sesquipedalis (L.) Verdc. and to evolve suitable management
measures.
A survey was conducted in six major yard long bean growing tracts of
Thiruvananthapuram district during 2015-16 to document the infestation of important
borer pests and their natural enemies. The biology of major borer pests were studied
under laboratory conditions and population dynamics through competitive exclusion
was studied by releasing the adults of two major pod borers simultaneously on to the
netted yard long bean plants. Ten varieties of yard long bean were collected and
evaluated for pod borer resistance, if any as per the field screening technique of Jackai
(1982). The in-vitro efficacy of microbial insecticides and field evaluation of selected
new generation insecticides and their combinations were conducted in managing the
borer pest complex of yard long bean.
Stem fly, Ophiomyia phaseoli (Tryon), girdle beetle, Nupserha bicolour
(Thoms.), blue butterfly, Lampides boeticus (L.) and spotted pod borer, Maruca vitrata
(G.) were the major borer pests which infested yard long bean at their different growth
stages. The infestation of O. phaseoli was recorded during seedling stage while N.
bicolour infestation occurred during vegetative stage of the crop. Among the six
panchayats/location, significantly highest number of girdles as well as plant infestation
were recorded from Balarampuram and the maximum intensity of infestation was
recorded during fourth week and it was found decreasing with increasing crop age. The
occurrence of L. boeticus was recorded from all the panchayats/location with the
highest pod infestation in Balarampuram panchayat, while the incidence of M. vitrata
was recorded only from two panchayats (Athiyannoor and Venganoor).
Correlation studies between the weather parameters and population dynamics of
pests revealed that per cent pod damage by M. vitrata showed significant positive
correlation with wind speed and negative correlation with rainfall, whereas, O. phaseoli
showed a significant negative correlation with the sunshine hours.
With regard to the biology studies, female girdle beetle was found to lay eggs
(0.54 mm x 0.13 mm) inside the growing stem by making punctures and girdles for
oviposition. The mean incubation period was 2.66 days. The larva is yellowish white,
soft-bodied with a dark head capsule which possesses an average larval period of 31.99
days and the pupation within the stem. The life cycle was completed in 67.63±7.75 days
on yard long bean. On biochemical analysis, the phenol content in the upper part of the
girdle infested stem was higher than lower part.
The eggs of L. boeticus were disc-shaped, finely sculptured and pale green
colour with an incubation period of 3.20±0.20 days. There were four larval instars and
last instar was slug like, pea green in colour. Its life cycle completes in 20-22 days. In
case of M. vitrata, the mean longevity of the adult was 6.00±0.57 days. There were five
larval instars which took 12.25±1.43 days to enter into pupal stage. Pupation took place
in the webbed flowers/pods and the pupal period lasted for about 8.25±0.75 days. The
life cycle was completed in 28.00±3.03 days.
From the population dynamics studies, it was revealed that L. boeticus was
dominant over M. vitrata based on the per cent pod and flower infestation.
In the varietal screening of yard long bean against borer pests, the cultivar VS-
13 was found resistant against O. phaseoli with significant variation in branches
infested per plant, while no significant variation was observed with respect to number of
girdles per plant and percentage plant infestation in the case of N. bicolour. The
cultivars VS-13 and VS-05 were found resistant against L. boeticus. The resistant
cultivar, VS-13 recorded less sugar content, high phenol and maximum pod length and
breadth when compared to other cultivars.
Efficacy of five microbial insecticides against pod borers viz., L. boeticus and M.
vitrata under laboratory conditions showed that Bt. var. kurstaki @ 1 g l-1 on 5 days
after treatment (DAT) recorded the highest mortality followed by B. bassiana and M.
anisopliae @ 107 spores ml-1.
Foliar application of chlorantraniliprole 18.5 SC @ 30 g a.i.ha-1 was effective
against O, phaseoli with the least feeding punctures per leaf (4.85) and adults per plant
(0.35) followed by seed treatment with acetamiprid 20 SP @ 20 g a.i.ha-1 in field
condition.
Field evaluation of insecticides against L. boeticus showed that indoxacarb 14.5
SC @ 75 g a.i.ha-1 recorded lowest pod infestation (11.98 per cent) which was followed
by flubendiamide 39.35 SC @ 48 g a.i.ha-1 (12.33 per cent) and thiacloprid 21.7 SC @
120 g a.i.ha-1 (12.40 per cent). In case of percentage flower damage, chlorantraniliprole
18.5 SC @ 30 g a.i.ha-1 followed by flubendiamide 39.35 SC @ 48 g a.i.ha-1 and
thiacloprid 21.7 SC @ 120 g a.i.ha-1 recorded low flower damage (5.68, 6.77 and 6.95
per cent) when compared to control (31.98 per cent).
Maximum crop yield was recorded from plots treated with emamectin benzoate
5 SG @ 10 g a.i.ha-1 (160.77 g plant-1) followed by chlorantraniliprole 18.5 SC @ 30 g
a.i. ha-1 (159.83 g plant-1) and flubendiamide 39.35 SC @ 48 g a.i.ha-1 (152.66 g plant-1)
while in untreated plot the yield was 93.11 g plant-1.
In the case of insecticide combinations against pod borer complex, seed
treatment with acetamiprid 20 SP @ 20 g a.i.ha-1 and foliar application of insecticide
combination (chlorantraniliprole 18.5 SC + flubendiamide 39.35 SC) at flowering stage
followed by foliar application of chlorantraniliprole 18.5 SC @ seedling stage and
combination (chlorantraniliprole 18.5 SC + flubendiamide 39.35 SC) at flowering stage
and seed treatment with acetamiprid 20 SP @ 20 g a.i.ha-1 at seedling stage and foliar
application of flubendiamide 39.35 SC @ g a.i.ha-1 were effective in reducing the
flower and pod damage with less larval population and maximum crop yield.
Among the borer pests of yard long bean, L. boeticus is the dominant pest based
on their infestation and occurrence, whereby its incidence is more closely associated
with crop stage rather than the weather parameters. From the biology studies, the vine
borer, N. bicolour is found to possess maximum longevity on yard long bean than other
borer pests. The resistant cultivars VS-13 and VS-54 could be utilized in future
breeding programme. With regard to management of borer pests, foliar application of
chlorantraniliprole 18.5 SC @ 30 g a.i.ha-1 was found effective in terms of percentage
reduction in the flower and pod damage, reduced larval population and increased crop
yield.