Survey and population dynamics of major insect pests

Survey and population dynamics of major insect pests and management of gall forming black
caterpillar (Betousa stylophora Swinhoe: Thyrididae) on Aonla (Emblica officinalis Gaertn)
Investigations on survey and population dynamics of major insect pests and management of gall forming
black caterpillar on aonla were carried out during 2001 to 2004 at Anand Agricultural University, Anand
and on farmer`s orchards in middle Gujarat.Results of the survey carried out in middle Gujarat revealed that
aonla fruit trees mainly attacked by different insect pests belonging to four major insect groups viz.,
Lepidoptera, Homoptera, Coleoptera and Isoptera. The major pests recorded were Betousa stylophora
Swinhoe, Gracillaria acidula (Meyrick), Selepa celtis Moore and Indarbela tetraonis Moore which belong
the order Lepidoptera, whereas Cerciaphis emblica Patel and Kulkarni, Nipaecoccus vastator (Maskell) and
Oxyrhachis tarandus Fabricius of Homoptera. The pest species Myllocerus discolor Boheman and termite
were also found damaging to this crop belong to the orders Coleoptera and Isoptera, respectively.
Among the natural enemies of these pests, two species of coccinellid beetles viz., Cheilomenes sexmaculata
Fabricius (Menochilus sexmaculata Fabr.) and Coccinella septempunctata Linn., four species of spiders
(Neoscona sp., Peucetia sp., Argiope sp. and Oxyopes sp.) as well as mantids were found praying on
different pests. Four parasitoids viz., Cotesia (Apanteles) ruficrus Holiday, Charops obtusus Morley and
Eucarcelia illota Curran on S. celtis; and Brachymeria sp. on B. stylophora were recorded.A study on
population dynamics of B. stylophora revealed that damage to twigs due to this pest commenced from first
week of June and it continued up to the first week of January. The damage ranged from 0.50 to 33.83 per
cent. Correlation between incidence and weather factors was worked out and the study indicated that
morning relative humidity (RH1), evening relative humidity (RH2), mean relative humidity (MRH),
morning vapour pressure (VP1), evening vapour pressure (VP2), mean vapour pressure (MVP), minimum
temperature (MinT) and rainfall (RF) showed significant positive correlation. Regression study showed 80
per cent variability in twig damage could be accounted by MinT, mean temperature (MT) and wind speed
Infestation of leaf roller (G. acidula) was started from second week of June which continued up to the fourth
week of November (0.09 to 15.24 % damage to leaflets). Among the different physical factors of
environment, MinT, RH1, RH2, MRH, VP1, VP2 and MVP exhibited positive correlation. Regression study
indicated that decrease in magnitude of MT, VP2 and WS in the range of 19.41 to 33.440C, 9.25 to 24.91
mm in Hg and 1.25 to 8.25 Kmhr-1, respectively were found favourable to this pest.
Population of aphid (C. emblica) was observed from fourth week of April to October. However, its higher
activity was recorded (0.76 to 4.34 index) from May to July. Correlation study indicated that MinT, VP1 and
VPD1 caused significant positive effect on this pest. The regression study revealed that 60.29 per cent
variation in population was due to maximum temperature (MaxT) and minimum temperature (MinT) in the
range of 31 to 41 and 23 to 280C, respectively.
Population of mealy bug (N. vastator) was recorded throughout the year which ranged from 0.17 to 13.27
per 10 twigs. The highest population of this pest was recorded during last week of December. MinT, MT,
MaxT, VP1 and MVP showed significant negative correlation indicating that increase in magnitude of these
weather elements resulted in reduction of mealy bug incidence.
A study on screening of fourteen varieties/ genotypes of aonla for their susceptibility to major insect pests
revealed that NA-7, Kanchan, Chakaiya, Krishna, LS-2, LS-3 and LS-4 registered lower
B. stylophora and proved resistant to this pest. Further, a study on effect of morphological characters and
biochemical contents of aonla twigs/leaflets on incidence of this pest indicated that twig length, number of
compound leaves and leaflets are the important characters for imparting resistant to aonla. Similarly,
moisture content, crude proteins, amino acids and total soluble sugars positively correlated, whereas total
phenols caused negative effect on this pest.
Aonla varieties LS-4, Anand-1, NA-7, LS-5, Banarsi, Gujarat Aonla-1 and Kanchan registered less than
5.32 per cent damage to leaflets due to leaf roller (G. acidula) and proved resistant. Length, width, thickness
and distance between two leaflets showed positive correlation and proved important for imparting
resistance. Similarly, higher content of total phenols and lower contents of crude proteins, amino acids and
total soluble sugars were the important in imparting resistance to aonla against this pest.
Banarsi, LS-1, Chakaiya, LS-2, LS-5, Kanchan and LS-6 recorded lower population of aphid (< 0.52
index) and found resistance. Similarly, lower population of mealy bugs (< 2.70/ 10 twigs) was also
recorded from varieties NA-7, Anand-1, Banarsi, Chakaiya, Krishna, LS-2, LS-5 and LS-6 and proved to be
resistant. However, none of the morphological or biochemical contents under study showed any correlation
in providing defense to trees against these pests.
Studies on evaluation of different IPM modules revealed that a module consisting of alternate applications
of azadirachtin (0.0005%) and monocrotophos (0.04%) at weekly interval during June and July found to be
effective for the management of gall forming caterpillar on aonla.