Management of sweetpotato Whitefly Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) on tomato using biorational pesticides (Neem, Abamectin and Spinosad) and UV-absorbing nets and films as greenhouse cover in the humid tropics [Elektronische Ressource] / von Prabhat Kumar

Prabhat Kumar

Description

Management of Sweetpotato Whitefly Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) on tomato using biorational pesticides (Neem, Abamectin and Spinosad) and UV-absorbing nets and films as greenhouse cover in the humid tropics Von der Naturwissenschaftlichen Fakultät der Universit t Hannover zur Erlangung des Grades Doktor der Gartenbauwissenschaften - Dr. rer. hort. - genehmigte Dissertation von M.Sc. Prabhat Kumar geboren am 27. December 1970 in Muzaffarpur, India 2005 Referent: Prof. Dr. Hans-Michael Poehling Korreferent: Prof. Dr. Hans-Juergen Tantau Tag der Promotion: 08.02.2006 ---- Dedicated to my late grandparents ---- Sri. Ramnandan Mishra ji & Smt. Ahilaya Devi Summary I Summary The sweetpotato (Whitefly, WF) Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) originates from tropical and subtropical regions, now having a worldwide distribution as a serious pest of open field vegetable production (Tropics, Sub-tropics and Mediterranean regions) and crops grown under protected cultivation. The short and multiple life cycles with high reproduction rates under tropical conditions, fast selection of resistant biotypes to different classes of insecticides including organophosphates, pyrethroids, cyclodiens and even first, second generation neurotoxin nicotinoids, and even growth regulators are major control constraints.

Informations

• Publié par: gottfried_wilhelm_leibniz_universitat_hannover
• Publié le: 01 janvier 2005
• Nombre de lectures: 14
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Management of Sweetpotato Whitefly Bemisia tabaci
Gennadius (Homoptera: Aleyrodidae) on tomato using
biorational pesticides (Neem, Abamectin and Spinosad) and
UV-absorbing nets and films as greenhouse cover in
the humid tropics










Von der Naturwissenschaftlichen Fakult?t
der Universit t Hannover
zur Erlangung des Grades


Doktor der Gartenbauwissenschaften
- Dr. rer. hort. -


genehmigte Dissertation
von


M.Sc. Prabhat Kumar
geboren am 27. December 1970 in Muzaffarpur, India


2005 Referent: Prof. Dr. Hans-Michael Poehling



Korreferent: Prof. Dr. Hans-Juergen Tantau



Tag der Promotion: 08.02.2006





---- Dedicated to my late grandparents ----


Sri. Ramnandan Mishra ji

&

Smt. Ahilaya Devi Summary I
Summary
The sweetpotato (Whitefly, WF) Bemisia tabaci Gennadius (Homoptera:
Aleyrodidae) originates from tropical and subtropical regions, now having a
worldwide distribution as a serious pest of open field vegetable production
(Tropics, Sub-tropics and Mediterranean regions) and crops grown under
protected cultivation. The short and multiple life cycles with high reproduction
rates under tropical conditions, fast selection of resistant biotypes to different
classes of insecticides including organophosphates, pyrethroids, cyclodiens and
even first, second generation neurotoxin nicotinoids, and even growth
regulators are major control constraints. In addition, the waxy shelters
protecting the immobile larval and pupal WF stages, high immigration and
generation time, wide range of hosts (over 600 plant species) are
characteristics that make its control extremely difficult.
Subject of the present studies were exploring the potential of the botanical
pesticides, neem using its various application methods and concentrations to
control WF and evaluating its persistency compared to so-called bio-rational
natural pesticides like spinosad and abamectin. In addition, physical control
strategy by using a combination of UV-blocking nets and plastics were explored
to learn their potential to manipulate the immigration behavior (entry) of WF and
other small sucking insect-pest of tomatoes like thrips and aphids taking into
consideration also the thrips related spread of a tospovirus.
In first series of experiments, neem was tested using three different treatment
methods (seed, soil and foliar) and two different commercial neem products
fi fi(NeemAzal T/S 1% Azadirachtin and NeemAzal U 17% Azadirachtin) against
WF on tomato plants. Studies were conducted in cages in air conditioned
cultivation rooms. All three methods of neem treatments resulted in reduced
colonization and oviposition by WF. Overall oviposition intensity was
significantly reduced by the treatment of tomato seeds (261 eggs in control
ficompared to 147 eggs at a dose-rate of 3.0g/l of NeemAzal U) but an even
higher reduction was achieved through soil drenching (345 egg in control
ficompared to 90 eggs at 3.0g/l of NeemAzal U) and foliar spraying (286 eggs in
fi)control compared to 53 eggs at 10 ml/l of NeemAzal TS. In contrast, in soil
and foliar treatment fecundity per female increased at highest tested
concentrations (from 19 eggs/female in blank treatments to 28 eggs per female
Summary II
fi fiat 3.0 g/l NeemAzal U and from 15 eggs/female to 22 at NeemAzal TS at 10
ml/l in foliar treatment). Reduced egg hatch could be observed only at high
neem concentrations; 62 and 51% of deposited eggs hatched at highest dose-
fi rates of NeemAzal U at 3.0 g/l in case of seed and soil drenching treatments
respectively; whereas only 43% of deposited eggs hatched in case of foliar
fitreatments at highest dose-rates of 10 ml/l using NeemAzal T/S. Seed (35%),
foliar (93%) and soil treatments (91%) caused a significantly higher mortality of
immatures and reduced number of hatching adults compared to control plants
treated with a blank formulation or water. The mortality amongst immatures
increased in relation to azadirachtin concentrations. Concerning susceptibility of
different developmental stages, young larvae showed the most sensitive
reaction. The most efficient treatment was foliar treatment, which achieved 100
% mortality for all three larval stages at high concentrations (10.0 ml/l of
fiNeemAzal T/S) compared to 78-87% mortality with soil treatment (at 3.0g/l of
fi NeemAzal U).
To further explore the possibilities of developing synergy with locally available
parasitoids of WF, persistence of foliar and systemic application of azadirachtin
was tested for 7 days (1,3,5 and 7) in air conditioned rearing rooms and tropical
netted greenhouses using the same two products described for the first
experiments. Foliar application induced under closed room conditions at dose-
rates of 7 and 10 ml NeemAzalTS/l immature mortality of 32 and 44 %
respectively 7-days post application, where as under greenhouse conditions
these rates declined to 5 and 7 % during the same period indicating rapid
dissipation of active ingredient. However, systemic application resulted in more
stable effects under both laboratory and greenhouse conditions. After soil
drenching with solutions of 3.0 g NeemAzalU/l until 7-d, immature mortality
declined from 88% for the first day to almost half (45%) on 7-d. However in case
of laboratory, it was 90% on first day and declined to 64% on 7-d post
application. Similar trends of responses of the B. tabaci were obtained for other
parameters like adult colonization, egg deposition and egg hatch. The loss of
efficiency of the neem products was clearly related to the dose-rate, methods of
application and environment (temperature and UV). Soil application is therefore
a convenient approach to achieve high efficiency and persistence with neem
products under the critical conditions in tropical greenhouse environments.
Summary III
In third experiments, direct and residual toxicity of NeemAzal TS (azadirachtin),
spinosad (Spinosyne) and abamectin (Avamectin) were tested against different
life stages of WF under laboratory conditions and in a tropical net greenhouse.
NeemAzal TS and abamectin deterred the settling of adults on the plant and
consequently reduced egg deposition. No such effect was detected for
spinosad. All three pesticides influenced egg hatch. Effects of NeemAzal TS
were significantly altered if applied to different aged eggs (1, 3, and 5-d old). In
contrast, abamectin treated eggs failed to hatch at any given age-class.
Moreover, spinosad and NeemAzal TS influenced egg hatch in a concentration
dependent manner. All three products caused heavy mortality of all three larval
stages of B. tabaci, where the first instar larvae was found to be most
susceptible compared to other two larval stages. Larval mortalities of 100%
were achieved with NeemAzal TS at twice the recommend dose-rate (10ml/l)
and at all tested concentrations of abamectin and spinosad. The daily mortality
rates were highest for abamectin, all treated larvae at every larval stage died
within 24 h post application. In contrast, 100% larval mortality in case of
NeemAzalTS and spinosad was reached 6-9 days post application. The daily
mortality rates were clearly concentration dependent. Abamectin caused 100%
immature mortality at all residue ages (1, 5, 10 and 15-d) in the laboratory and
greenhouse as well. Persistence of spinosad was comparable high in the
laboratory but in the greenhouse a faster decline of activity was evident by
increased egg deposition, egg hatch and reduced rates of immature mortality.
Toxicity of NeemAzalTS however strongly declined under greenhouse
conditions with time (5-d) post application.
The last series of experiments explored the possibility of integrating UV-
blocking nets and plastics to develop appropriate physical control strategies for
WF. The studies were conducted to investigate the effect of ultraviolet blocked
greenhouses made from combination of net and plastics on the immigration of
three important pest of tomatoes; WF (Bemisia tabaci), thrips (Ceratothripoides
claratris), and aphid (Aphis gossypii) and occurrences of viruses e.g. tospovirus.
Fewer WF, aphids and thrips immigrated and consequently were trapped either,
when gates kept open whole day (complete ventilation) or partially open from
6.00 10.00 (partial ventilation) in greenhouses made from the combination of
UV-blocking nets and plastics compared to non UV-blocking nets and plastic
Summary IV
greenhouse. Similarly, significantly less number of alate aphids and adult B.
tabaci/leaf were counted within greenhouses with low intensity of the UV over
those with more UV light intensity. Thrips were the most occurring pests, that
too were recorded significantly less under GH with lower UV-intensity and
consequently significantly lower levels of leaf damage were recorded under
these greenhouses. During, open gates experiments (complete ventilation), a
96-100% virus infestation was recorded under non UV-blocking greenhouses
compared to 6-10% under UV-b