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common name: bean flower thrips
scientific name: Megalurothrips usitatus (Bagnall) (Insecta: Thysanoptera:Thripidae)

Introduction - Distribution - Synonymy - Description - Life Cycle and Biology - Host Plants - Economic Importance - Management - Selected References



Introduction (Back to Top)

Megalurothrips usitatus (Bagnall, 1913) is a small sized (3-4 mm) (Fig. 1) insect in the order Thysanooptera and family Thripidae. Megalurothrips usitatus is commonly known as bean flower thrips, oriental bean thrips, and Asian bean thrips. Meagalurothris usitatusis an important economic pest of legumes (Mound and Walker 1987, Palmer 1987). Megalothrips usitatus is reported to cause feeding injury in bean flowers in south China (Tang et al. 2015) and Florida (Soto-Adames 2020). Thrips infesting beans like Megalurothrips usitatus are commonly found in flowers, causing feeding injury and leading to crop loss.


Image= Megalurothrips_usitatus01.jpg Figure 1. Adult female (A) and male (B) bean flower thrips, Meagalurothris usitatus Bagnall (dorsal view). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida

Image= Megalurothrips_usitatus01.jpg
Figure 1. Adult female (A) and male (B) bean flower thrips, Meagalurothris usitatus Bagnall (dorsal view). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.



Synonymy (Back to Top)


Distribution (Back to Top)

Megalurothrips usitatus is widely distributed in India, Bangladesh, Pakistan, Srilanka, the southern region of China, Japan, and Fiji (Kalpana et al. 2011, Tang et al. 2015). In Australia, Megalurothrips usitatus was reported in northern Australia, Western Australia to Queensland and north to New South Wales. Megalurothrips usitatus was first reported in the USA in Florida in 2020 (Soto-Adames, F. N. 2020).



Description (Back to Top)

Megalurothrips usitatus adults are dark brown in color. Both male and female Megalurothrips usitatus are fully winged. The head is as wide as long, conspicuously transversely reticulate at posterior. The antenna is 8-segmented, antennal segments I-II brownish yellow, segment I with pair of dorso-apical setae, segment III yellow to light brown, and segment III-IV with constricted apical neck, sensorium forked (Fig. 2).


Image= Megalurothrips_usitatus02.jpg Figure 2. Head of an adult bean flower thrips, Meagalurothris usitatus Bagnall, showing antenna with eight antennal segments (A) and enlarged view of one antenna (B) (arrow showing the constricted apical neck between segment III-IV). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.

Image= Megalurothrips_usitatus02.jpg
Figure 2. Head of an adult bean flower thrips, Meagalurothris usitatus Bagnall, showing antenna with eight antennal segments (A) and enlarged view of one antenna (B) (arrow showing the constricted apical neck between segment III-IV). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.



Megalurothrips usitatus has three pairs of ocellar setae, pair III on anterior margins of ocellar triangle and longer than distance between compound eyes (Fig. 3). The postocular setae are small.



Image: Megalurothrips_usitatus03.jpg Figure 3. Head of an adult bean flower thrips, Meagalurothris usitatus Bagnall, showing ocelli and ocellar setae (Red circle). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.

Image: Megalurothrips_usitatus03.jpg
Figure 3. Head of an adult bean flower thrips, Meagalurothris usitatus Bagnall, showing ocelli and ocellar setae (Red circle). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.



The pronotum has two pairs of long posteroangular setae, outer longer than inner, posterior margin with three pairs of setae, anteroangular setae well developed (Fig. 4). The mesonotum has transverse reticulation lateral setae. The metanotum has weak sculpture, campaniform sensilla present, median setae long, arise at anterior margin. All tarsi are two-segmented, apices of mid and hind tibiae and most part of fore tibia yellow, hind tibia with two stout dark apical setae.



Image: Megalurothrips_usitatus04.jpg Figure 4. Head and thorax (Pro, meso and meta thorax) of an adult bean flower thrips, Megalurothrips usitatus Bagnall, showing (A) prothoracic (red circle) and (B) meta-thoracic setae (blue circle). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.

Image: Megalurothrips_usitatus04.jpg
Figure 4. Head and thorax (Pro, meso and meta thorax) of an adult bean flower thrips, Megalurothrips usitatus Bagnall, showing (A) prothoracic (red circle) and (B) meta-thoracic setae (blue circle). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.



The fore wings are brown with basal quarter pale and an extensive pale area sub-apically. The first vein of fore wing has long row of setae before distinct sub-apical gap followed by 2 setae, and second vein has complete row of setae, postero-marginal cilia wavy (Fig.5).



Image: Megalurothrips_usitatus05.jpg Figure 5. Wings of an adult bean flower thrips, Megalurothrips usitatus Bagnall. Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.

Image: Megalurothrips_usitatus05.jpg
Figure 5. Wings of an adult bean flower thrips, Megalurothrips usitatus Bagnall. Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.



The abdominal tergites II-VIII are without sculpture medially, but lateral thirds with sub-parallel lines, median setae small, ctenidia absent. The VIII abdominal tergite has irregular group of microthichia antero-mesad of spiracle, posteromarginal comb of slender microtrichia but broadly absent medially (Fig. 6 and Fig. 7). The tergite X has incomplete longitudinal split. The sternites are without discal setae, three pairs of long marginal setae, median pair of marginal setae on sternite VII arise in front of margin.



Image: Megalurothrips_usitatus06.jpg Figure 6. Abdominal tergite of female adult bean flower thrips, Megalurothrips usitatus Bagnall, showing incomplete comb at eighth abdominal segment. Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.

Image: Megalurothrips_usitatus06.jpg
Figure 6. Abdominal tergite of female adult bean flower thrips, Megalurothrips usitatus Bagnall, showing incomplete comb at eighth abdominal segment. Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.



Image: Megalurothrips_usitatus07.jpg Figure 7. Abdominal tergites of a female adult composite thrips, Megalurothrips usitatus Bagnall, showing incomplete comb at eighth abdominal segment (A) and ovipositor (B). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.

Image: Megalurothrips_usitatus07.jpg
Figure 7. Abdominal tergites of a female adult composite thrips, Megalurothrips usitatus Bagnall, showing incomplete comb at eighth abdominal segment (A) and ovipositor (B). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.


The male Megalurothrips usitatus is smaller and paler than the female. The pronotum and legs of the male Megalurothrips usitatus are yellow. The abdominal tergite IX posterior margin without paired setiform processes, posterolaterally with pair of short very stout setae, and sternites without pore plates (Fig. 8).


Megalurothrips usitatus female is difficult to identify from several other related species (i. e. M. distatalis, M. formosae, M. mucunae and M. peculiaris). The male specimens of the species can provide the ultimate correct identification (Palmer 1987).



Image: Megalurothrips_usitatus08.jpg Figure 8. Abdominal tergites of male adult bean flower thrips, Megalurothrips usitatus Bagnall, showing abdominal tergite IX with pair of short and very stout setae (A) and copulatory organ (B). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.

Image: Megalurothrips_usitatus08.jpg
Figure 8. Abdominal tergites of male adult bean flower thrips, Megalurothrips usitatus Bagnall, showing abdominal tergite IX with pair of short and very stout setae (A) and copulatory organ (B). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.


Life Cycle and Biology (Back to Top)

The life stages of Megalurothrips usitatus include two larval instars, prepupa, pupa and adult. The early larval instars (1st and 2nd) look white while the later stage of the 2nd instar larva and prepupa look yellow to orange color. The developmental period from egg to adult depends on the host plants. Tang et al. (2015) reported Megalurothrips usitatus took 9.53±0.06, 10.62±0.14, 11.20±0.11, and 11.55±1.13 days to complete life cycle on snap bean (Phaseolus vulgaris L.), cowpea (Vigna unguiculata L.), pea (Pisum sativum L.) and lima bean (Phaseolus limensis Macf.) pods, respectively. The intrinsic rate of increase (rm) and net reproductive period (RO) of Megalurothrips usitatus was observed higher on snap bean compared to other beans. Megalurothrips usitatus can reproduce both sexually and parthenogenetically. Megalurothrips usitatus that reproduces parthenogenetically, lived longer and had longer oviposition periods and greater fecundity (Tang et al. 2015). Greater mortality of larvae during pupation was observed in soil with low sand content and less than 2% moisture content (Chang 1989). Adult Megalurothrips usitaus are mostly active between 8:00-10:00 am while being inactive at night. Megalurothrips usitatus exhibit aggregation behavior which is thought to be due to the male-produced aggregation pheromone (Liu et al. 2020). Megalurothrips usitatus male and females are found aggregated on the host and their numbers increased after the mid-blooming stage. The larval population was distributed randomly. However, as their number increased, the distribution became contagious (Chang 1992). The number of larvae peaked five to seven days later than the adult population (Chang 1988).



Image: Megalurothrips_usitatus09.jpg Figure 9. Immature stages of Megalurothrips usitatus Bangall, showing last larval instar (A) and first, second and third larval instars (B). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.

Image: Megalurothrips_usitatus09.jpg
Figure 9. Immature stages of Megalurothrips usitatus Bangall, showing second larval instar (A) and first and second larval instars (B). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.



Image: Megalurothrips_usitatus10.jpg Figure 10. Adults of Megalurothrips usitatus Bangall (red circle), on bean leaf showing the feeding injury (blue rectangle) (A and B). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.

Image: Megalurothrips_usitatus10.jpg
Figure 10. Adults of Megalurothrips usitatus Bangall (red circle), on bean leaf showing the feeding injury (blue rectangle) (A and B). Photograph by Rafia A. Khan, Entomology and Nematology Department, University of Florida.



Host plants (Back to Top)

Megalurothrips usitatus was found on 28 plant species in nine families and 16 of the species belonged to the Leguminosae (Chang 1987). Various Leguminosae crops in the genus Glycine, Arachis, and Vigna are hosts of Megalurothrips usitatus. Important hosts of Megalurothrips usitatus includes mung bean (Vigna radiate (L.) R. Wilczek), snap bean (Phaseolus vulgaris L.), cowpea (Vigna unguiculata L., pea (Pisum sativum L.), lima bean (Phaseolus limensis Macf.), groundnuts (Arachis hypogaea L.), pigeon-pea (Cajanus cajan (L.) Millsp), yard-long bean (Vigna unguiculata subsp. sesquipedalis L.), matura tea tree (Cassia auriculata L.), Calandine Spider Flower (Cleome chelidonii L.), sunn hemp (Cratalaria juncea L.), Caracas Rattlebox (Crotalaria micans L.), variable-leaf ticktrefoil (Desmodium heterophyllum DC.), Indian coral tree (Erythrina variegate L.), Mexican lilac (Gliricidia sepium Walp.), hiptage (Hiptage benghalensis L.), tropical kudzu (Pueraria phaseoloides Benth.), vegetable hummingbird (Sesbania grandiflora L.), black gram (Vigna mungo L.), and soybean (Glycine max L. Merr) (Fletcher 1917, Palmer 1987, Tillekarratne et al. 2011, Sani and Umar 2017, Tang et al. 2015, Zafirah and Azidah 2018).



Economic Importance (Back to Top)

Megalurothrips usitatus, like other legume thrips, can cause an 80-100% yield reduction in legume crops (Oparaeke 2006). Both larvae and adults feed on flower buds.  Megalurothrips are commonly associated with injury to bean crops through feeding in the flowers, resulting in deformity and abortion of pods. However, Megalurothrips usitatus can feed on young leaves and pods of leguminous when flowers are not available (Tang et al. 2015). In mung bean, Megalurothrips usitatus can cause 13% to 64% yield losses through several infestations (Farajallah 2013). It was also reported that the presence of 13 individuals of Megalurothrips usitatus on untreated pigeon pea caused 36% of pod reduction (Rawat et al. 1969). Megalurothrips usitatus is one of the vectors of Tobacco Streak Virus (TSV).  Transmission of TSV occurs when Megalurothrips usitatus carries TSV infected pollen from the infected plants on their bodies and inoculates virus to the new host while feeding on plant tissue (Reddy et al. 2002, Prassda Rao et al. 2003, Shukla et al. 2005).



Management (Back to Top)

Sampling and monitoring
Blue sticky traps are the most attractive to Megalurothrips usitatus (Yan et al. 2017). The male produced aggregation pheromone of Megalurothrips usitatus can be used to develop commercial lures to monitor the pest and mass trapping (Liu et al. 2020).

Chemical Control
Insecticides of different modes of action used in different regions of the world provided suppression of Megalurothrips usitatus. (Hossain 2015, Sujatha and Bharpoda 2017, Yasmin et al. 2019, Maradi et al. 2020).  Heavy application and frequent use of these insecticide can have an adverse effect on the environment, humans and other living organisms as well as interrupting the biological balance between natural enemies and insect pests. There is a growing concern to develop environmentally friendly and biodegradable insecticides to manage Megalurothrips usitatus. Alternative to conventional insecticides, neem seed powder, garlic, ginger, papaya, and ginger rhizome extracts were effective in suppressing the population and intensity of Megalurothrips usitatus attack on mung bean. (Farajallah 2013, Srinivasan et al. 2019). However, these alternative bioproducts need to be fully evaluated.

Biological Control
The eulophid wasp, Ceranisus menes, was identified as a parasitoid of Megalurothrips usitatus in an adzuki bean field in Taiwan (Chang 1990) and in the Philippines (Loomans 2006). Minute pirate bug Orius maxidentex Ghuri (Hemiptera: Anthocoridae) is a natural predator used against Megalurothrips usitatus in India (Men 1999). Lee et al. (1991) found that Orius strigicollis (Poppious) effectively reduced the Megalurothrips usitatis on adzuki beans and sweet potatoes in Taiwan. In China, Orius sauteri (Poppius) is a significant predator of Megalurothrips usitatus. In a laboratory study, female and male Orius sauteri can consume an average of 304.7 and 104 thrips over their lifetimes, respectively (Liu et al. 2018). Microbial pathogens, Bacillus thuringiensis and Metarhizium anisopliae formulations effectively managed Megalurothrips usitatus population (Srinivasan et al. 2019). Entomopathogenic fungi, isolates of Akanthomyces attenuatues (SCAUDCL-38 and SCAUDCL-56), can cause 76.25% and 57.5 % mortality of adult Megalurothrips usitatus after five days of treatment with 1 × 108 conidia/ml (Du et al. 2019).

Cultural Control
Heavy rainfall reduces the population of Megalurothrips usitaus on pigeon pea (Dialoke 2013). As Megalurothrips usitatus is a vector of TSV, tall border crops such as sorghum, pearl millet and castor can serve as a barrier for thrips coming from a nearby infected area (Prassda Rao et al. 2003). Avoiding planting next to the infested field, or next to a kudzu patch, rotating crops with non-host crops (non-legume plants), can break the lifecycle of Megalurothrips usitatus. Intercropping with a non-host plants like capsicum between yard long beans can slow thrips movement through the crop. Before planting beans, the edge and surrounding areas around the bean fields should be properly sanitized to destroy wild hosts (Jackson 2017).


Selected References (Back to Top)

Authors: Rafia A. Khan, rkhan@ufl.edu, Dakshina Seal, dseal3@ufl.edu, and Rosan Adikari, adhikarirosan@ufl.edu, UF/IFAS, Entomology and Nematology Department, Tropical Research & Education Center.
Photographs: Rafia A. Khan, Entomology and Nematology Department, University of Florida.
Map: The Polistes Corporation created by Discover Life
Web Design: Kay Weigel
Publication Number: EENY-777
Publication Date: October 2021

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Featured Creatures Editor and Coordinator: Dr. Elena Rhodes, University of Florida