Tomato is a highly cultivated vegetable in Tanzania. The intensive tomato cultivation
and production in Tanzania has resulted in high pests and diseases build-up. A survey
to identify and quantify entomofauna diversity in different seasons and pest
management practices in Meru District was conducted. In addition, a laboratory
experiment was done to assess the effectiveness of commonly used pesticides
SnowBecco (Thiamethoxam) and Belt (Flubendiamide) against two dominating insect
pests, white flies (
Bemisia tabaci
(Gennadius, 1889)) and leaf miner (
Tuta absoluta
(Meyrick, 1917)), respectively. The results obtained revealed that, tomato fields in
Meru District had significantly higher entomofauna build up during dry season than the
rainy season (U
0.05 (df, 24) = 45, p = 0.0441). More than 70% of all collected
entomofauna were dominated by the whiteflies (
Bemisia tabaci) and tomato leaf miners
(
Tuta absoluta) belonging to orders Hemiptera and Lepidoptera, respectively. It was
also observed that, the common pesticides management practices were the use of
pesticidal cocktail, broad spectrum insecticides, use of botanical pesticides, frequent
application of pesticide and insecticides over dosage. Moreover, yield reduction due to
whiteflies and tomato leaf miners infestation were observed in terms of reduced fruits
number per plant (38 and 18.4%), fruit size (22.4 and 14.2%), and fruits weight per
plant by 43.6 and 26.2%, for
Bemisia tabaci and
Tuta absoluta, respectively. The study
showed that the recommended doses in both tested insecticides caused significant pest
mortality (F
0.05 (df, 19) = 4.367, p = 0.0199) and (F
0.05 (df, 19) = 4.761, p = 0.0147) for
B. tabaci and
T. absoluta, respectively, within a specified period of time. The results
suggest that high insect pest infestations could be caused by factors other than
development of insecticidal tolerance including inappropriate identification of insect
pests due to lack of training, and inappropriate selection and application of insecticides.
Consequently, frequent application of broad spectra insecticides not only increases
production expenses but also disrupts agroecosystem by killing beneficial entomofauna
and disrupting soil organisms that are susceptible to insecticide toxicity.
