Abstract
Megalurothrips sjostedti Trybom is an important pest of cowpea (Vigna unguiculata L.) in Africa. To propose an alternative to chemical control, the repellency of 24 plant extracts was evaluated against adult female thrips of M. sjostedti in the laboratory. Plant extracts in ethanol were separately applied on a filter paper disk in a still air visual cue olfactometer. The results showed highly significant differences in repellency among extract type, concentration and their interactions. We classified the level of repellency into four categories as strong, good, moderate and weak or non- repellent based on hierarchical ascendant classification. We identified Piper nigrum, Cinnamomum zeylanicum, Cinnamomum cassia as strong repellents. Five extracts were classified as good, eight as moderate and the remaining eight extracts were weak or non-repellent. Repellency of the extracts increased with the concentration suggesting that the behavioral response of M. sjostedti was dose-dependent. Mono- and sesquiterpene hydrocarbon compounds from seven highly repellent extracts were identified by gas chromatography-mass spectrometry (GC/MS). The use of repellent extracts could be useful in developing integrated pest management strategies for thrips on legume crops. In this regard, the specific modes of action of the identified compounds need to be investigated to incorporate them into the existing crop protection strategies.
Highlights
The Legume Flower Thrips (LFT), Megalurothrips sjostedti Trybom (Thysanoptera: Thripidae), is one of the most serious insect pests of leguminous plants including cowpea in tropical Africa [1,2,3,4].Thrips occur on legumes in every growing season, and their direct feeding causes destruction of buds and flowers as well as malformations of pods [5]
Among the three observation sections of the olfactometer, 52% of the thrips were observed in the top of the olfactometer, while 34% and 13% of the thrips were observed at the bottom and the middle of olfactometer, respectively, when considered irrespective of doses, extracts and time of exposure (F2, 3063 = 1840, p < 0.001)
The still-air visual and odor cue olfactometer used in the present study provided the opportunity to test the repellency response of legume flower thrips (LFT) to a combination of visual and olfactory cues, which is in line with the host response behavior of thrips [25,26]
Summary
The Legume Flower Thrips (LFT), Megalurothrips sjostedti Trybom (Thysanoptera: Thripidae), is one of the most serious insect pests of leguminous plants including cowpea in tropical Africa [1,2,3,4]. Thrips occur on legumes in every growing season, and their direct feeding causes destruction of buds and flowers as well as malformations of pods [5]. Yield losses ranging from 20% to 100% have been reported on cowpea (Vigna unguiculata L.) from different areas of Africa where modern pest control measures are absent [1,4]. The control of M. sjostedti in Sub-Saharan African countries relies heavily on synthetic insecticide application [6]. Pesticides from plant-based extracts have been suggested as a better alternative to synthetic insecticides [11]
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