Introduction insect has been reported since the 1990s

Introduction

The
tomato leaf miner Tuta absoluta (Meyrick)
(Lepidoptera: Gelechiidae) is a serious pest of tomato and other
vegetables (Miranda et al.,
1998). The
pest originated from South America and spread to Europe, the
Middle East, Africa and South Asia (Deusneux, 2011). The pest was reported in Africa,
North of the Sahel in 2008 (NAPPO, 2012), Western Africa in 2010, Sudan and
Ethiopia in 2012, Kenya in 2013, Tanzania and India in 2014 (Muniappan, 2014). In 2011, T. absoluta infested
1.0 M ha of tomato worldwide, which corresponds to 22% of the
cultivated area. Now it is a threat to Asia and
Africa (South of Sahara). In Spain, during the first year
of occurrence of T. absoluta,
pesticides were applied 15 times per season and the
cost went up by 450 Euro per ha. When T. absoluta invades the rest
of the world, the tomato pest management cost will go up by $500 M per year
(Muniappan, 2014).

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The damage is caused by the larvae of the insect, which feed and
grow on soft tissues, such as  leaves,
shoots and fruits and causes great reduction in the quantity and quality of
fruits yields, but also it can occur during all crop cycle (Torres et al., 2001).

The main method of controlling T. absoluta in South America was through
the use of synthetic pesticides, the low efficiency of the active ingredients
against the
insect has been reported since the 1990s
(Campos et al., 2014). Moreover,
use of synthetic pesticides poses a threat to the environment and health of
tomato consumers (Mtui et al., 2015), besides that it increases
production costs of up to 20 percent (Reis et
al., 2005).

The overuse of pesticides pose an
environmental problems and have been a matter of concern for both scientists
and the public
in recent years (Opender et al., 2008; Yusufu et al., 2011). Thus, there is a
need to look for the biodegradable and environmental friendly pesticides and
develop techniques that can be used to reduce pesticide use while maintaining
crop yields.

Extracts of many higher plants are
reported to exhibit antibacterial, antifungal and insecticidal properties under
laboratory and field tests. Natural products isolated from plants may be the
alternatives as they are known to have minimal environmental impact and danger
to consumers in contrast to synthetic pesticides (Yusuf et al., 2011).

In this study, three medicinal plants namely Synadenium glaucescens,
Commiphora swynnertonii and Allium
sativum have been used in the Tanzania traditional medicine (Nonga et al., 2013; Mabiki
et al., 2013; Bakari, 2013)

Previous findings show a broad spectrum of activity against
common pathogen in human and animals (Bakari et al, 2011; Mabiki et al., 2013). The
exudates of C. Swynertonii have been
used traditionally to cleanse bladder and kill insects such as ticks, lice, bed
bugs and mange mite. Garlic oil which is also an oviposition deterrent
has been found to be highly toxic to eggs of P. Xylostella. (Lanzotii, 2006; Kaonekane, 2007). Stem branches and buds of S.
glaucescens have insecticidal and repellant properties against aphids,
grasshoppers and mosquitoes (Grainge and Ashmed, 1988). This study aimed to determine the
effectiveness and the lethal dose of Commiphora swynnertonii, Synadenium glaucescens and Allium sativum crude extracts in controlling T. absoluta in tomatoes in Morogoro,
Tanzania specifically, to
determine the in vitro effectiveness
of different plants extracts against T. absoluta at two different life stages (egg and larvae) and to assess the in
vitro lethal concentration 50 of plant extracts against T. absoluta on
egg, larvae

 

Materials
and methods

The
experiment was conducted from March to June 2016 in the laboratory at Sokoine
University of Agriculture (SUA) Morogoro, Tanzania (6.822 S 37.661 E). Plants
extracts were prepared in the laboratory at the Department of Veterinary Medicine
and Public Health, while Tuta absoluta
were reared and monitored in an insecterium at the Horticulture Unit.

Roots of Synadenium
glaucensens were collected from Gairo district in Morogoro Region, while
bulbs of Allium sativum were
purchased from the Mawenzi market in the Morogoro Municipality. Extract of Commiphora swynnertonii was obtained
from the Natural Products Laboratory in the Department of Veterinary Medicine
and Public Health.

 

Experimental set up and data
collection

We used
a 3×3 factorial (Extracts from 3 plants species x 3 plants extract
concentrations) arranged in a completely randomised block design with three replications.
A synthetic insecticide BELT®SC (480g/l
Flubendiamide, Buyer AG, Leverkussen, Germany) was used as a positive control,
whereas sterile distilled water (SDW) containing 0.1% Tween® 20 was used as the negative
control.
The
insecticide was used as per the manufacturer’s recommendations at the rate of
15ml/100L.

Plant parts that were used in the experiment included;
root bark (S. Glaucensens), resin (C. Swynnertonii) and bulb (A. sativum). The plant materials were collected and packed into polyethylene bags, which
were transported to the laboratory within 24 h. The plant
materials were cleaned of debris using running tap water. Plant barks were first
peeled from root stumps  chopped into small pieces and sun
dried. Allium Sativum powder was prepared according to method described
by Mahmood (2009). The bulbs were cleaned and aseptically cut into small pieces
with a knife and then dried in the shade for 7 days at 32 – 35ºC. The
semi-dried pieces were then blended using pestle and mortar, and left to dry in
the shade at room temperature for further 7 days.
The materials were thereafter finely powdered using a mixer-grinder and
then stored in airtight bags in a cool dry room. The resin was just kept in
airtight bottle and stored in a fridge.

Solvent extraction was carried out according to the
method described by Parekh and Chanda (2007) with some modification. Each elite
plant powder (resin) was separately extracted in ethanol (99.8%).  Exactly 100 g of ground plant material was
soaked in 500 ml of ethanol in a conical flask plugged with aluminium foil and
kept for 72 h in a dark place at room temperature. The extracts,
were filtered with Whatman filter paper 1 from
Sigma-Aldrich and the filtrates were concentrated using a rotary evaporator until all
the solvent was cleared. The extracts were weighed to determine the percentage
of paste in the dry material and then were stored at 4°C in airtight bottles. The serial dilution method was used to prepare the
working solutions at the three different concentrations of 2%, 4% and 8% v/v.

Bioassay
was performed with second instars larvae using 2%, 4% and 8% concentrations of
each plant extract. The second instars larvae (25 larvae) were carefully
extracted from their mines by zero brush and then transferred to uninfected
tomato leaves in a Petri-dishes (15 cm in diameter). The uninfected tomato
leaves were soaked in extract solution for 10 seconds, air dried and then
introduced to the larvae. The Petri-dishes were lined with filter papers to
protect the larvae from excessive humidity. Each leaf was wrapped in humid
cotton wool to maintain turgor of the petiole. Petri-dishes were maintained at
conditions of the insectariums at 24±2°C. The positive and negative
control treatments as described in section 3.3 were also included. Each
treatment was replicated three times. The numbers of live and dead larvae of
each treatment as well as control were recorded after 1,2,3,4 and 5 days of
treatment.

Emerged,
moths were provided with 10% honey solution and allowed to mate for one day in
a 60x60x75 cm rearing cages. Plants with four to six true leaves (5 weeks seedlings) were transferred
to the rearing cages and maintained for two to three days for adults to lay
eggs. Leaflets of the tomato’s plants 
were examined under binocular microscope and T. absoluta eggs were counted  then extracted and  placed into Petri dishes (15 cm diameter) containing
a tomato leaf treated by the dipping method. The status of treated eggs was recorded as live
(hatched larvae) or dead (unhatched).  The egg bioassay was repeated three times.

 Data Analysis

Effectiveness of treatment in the laboratory were
compared by Two-way Analysis of Variance (ANOVA). Descriptive statistics (mean,
standard error of mean and coefficient of variation) were generated using GENSTAT
procedures. Post Hoc Tukey test was used to compare means Lethal Doses 50 of
each plant extract were determined by probit regression dose-response analysis
using MedCalc software version 17.6.

 

Results

Results showed variables effects of plants extracts on hatchability of T.
absoluta eggs in the laboratory. In vitro egg hatchability
was significantly (p