MSc

Spider mites (Prostigmata: Tetranychidae) cause severe injury to
vegetables grown under both protected and open field conditions. Awareness on
the ill effects associated with the use of synthetic chemicals in pest management
has resulted in an increased demand for safe to eat food. Hence, ecofriendly
strategies for the management of mite assume high priority. Investigations on
potential natural enemies of spider mites by All India Network Project on
Agricultural Acarology (AINPAA) have identified an acaropathogenic fungus,
Acremonium zeylanicum (Petch) Gams and Evans from the spider mite,
Tetranychus urticae Koch on brinjal from Thrissur district.
The present study was undertaken at the Department of Agricultural
Entomology, College of Horticulture, Vellanikkara during 2016 - 2017 in the
above context to investigate the biocontrol potential of the acaropathogen, A.
zeylanicum against the predominant species of spider mite in Kerala, Tetranychus
truncatus Ehara; to assess the sensitivity of the acaropathogen to selected novel
acaricides and botanicals and also to evaluate its safety to the predatory mite,
Neoseiulus longispinosus (Evans).
Laboratory bioassay conducted to evaluate the efficacy of A. zeylanicum at
five different concentrations viz.1×105, 1×106, 1×107, 1×108 and 1×109 spores ml-1
against T. truncatus recorded more than 50 per cent mortality of adult mites
within six days at both 1×108 and 1×109 spores ml-1. The mortality increased with
increase in concentration of the fungus and also with progress in time. The highest
mortality of 68.36 per cent was recorded by A. zeylanicum applied at the rate of
1×109 spores ml-1 seven days after treatment, which was on par with 61.65 per
cent mortality recorded at 1×108 spores ml-1. The fungus was more effective
against adult stage compared to egg stage of T. truncatus. The highest mortality of
egg stage (41.33%) was recorded four days after the treatment at 1×10 9
spores ml-1.
Acremonium zeylanicum was evaluated along with two novel acaricides
and two botanicals against T. truncatus on cucumber under polyhouse conditions.
A. zeylanicum significantly reduced mite population seven days after treatment at
both 1×108 spores ml-1 (72.71%) and 1×107 spores ml-1 (55.03%). However the
novel acaricides (spiromesifen & diafenthiuron) and botanicals (neem oil &
azadirachtin) were significantly superior to the acaropathogen in reducing the mite
population.
Compatibility study of A. zeylanicum with different agrochemicals
revealed that the acaricides, spiromesifen and fenpyroximate were relatively safer
to the fungus. The fungicides, Curzate M8 (Cymoxanil 8% + Mancozeb 64 %)
and Equation Pro (Fomaxadone 16.6%+ Cymoxanil 22.1%) recorded highest per
cent inhibition and were followed by the acaricides, fenazaquin, diafenthiuron,
propargite and the botanicals azadirachtin and neem oil. Laboratory evaluation of
safety of A. zeylanicum to the predatory mite N. longispinosus showed that the
predatory mite was less susceptible to A. zeylanicum than the prey mite,
T. truncatus. The pathogen did not have any ovicidal effect and had caused much
lower mortality of 20 per cent on adults of N. longispinosus at the highest dose of
1×108 spores ml-1.
The study indicated the potential of A. zeylanicum in reducing mite
population significantly both in laboratory and polyhouse. The pathogen was
found to be compatible with commonly used acaricides and also was safe to the
predominant predatory mite species in vegetable ecosystems. Thus it can be
inferred that the acaropathogen A. zeylanicum could be a valuable component in
integrated mite management programme in vegetables.