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Megoura crassicaudaJapanese vetch aphid, Bean aphidOn this page: Identification & Distribution Other aphids on the same host Damage & ControlIdentification & DistributionAdult apterae of Megoura crassicauda are green with black head, prothorax, antennae, siphunculi and cauda, dusky mesothorax, and variably pigmented tibiae. The antennae are 0.9-1.1 times the body length, with a terminal process about 4 times as long as the base of antennal segment VI. The species is very similar to the European Megoura viciae, differing only with respect to the number of secondary rhinaria on the antennae. Antennal segment III has 21-50 secondary rhinaria in a row extending over 0.75-0.90 of the segment (cf. Megoura viciae, which has segment III with 5-26, usually 10-18, rhinaria, not in a row, on basal 0.75 of segment). The rostrum reaches to just past the middle coxae. The apical rostral segment (RIV+V) is 0.63-0.87 times the second hind tarsal segment (HTII). The abdomen has antesiphuncular and small postsiphuncular sclerites, and short cross bands on tergites VII & VIII. The siphunculi are cigar shaped, about 0.16 times body length, and the same length as the cauda. The body length of adult Megoura crassicauda apterae is 3.0-3.7 mm. Note: Mordvilko (1919) originally described this species as Megoura viciae subsp. crassicauda. Miyazaki (1971) used Megoura japonica for the same species, a name still used in some of the literature about Megoura crassicauda.
First picture above copyright Department of Primary Industries, New South Wales, Australia; The alate Megoura crassicauda has the head and thorax black, the abdomen green with black marginal, ante- and post-siphuncular sclerites, and cross bands on tergites VII and VIII. The antennae are slightly longer than the body. Antennal segment IV has more than 17 rhinaria (cf. Megoura viciae alate, which has 0-7 secondary rhinaria on segment IV). Megoura crassicauda is monoecious on the stems and growing points of beans (Vicia spp.) and vetches (Lathyrus spp.). It has also been recorded from garden pea (Pisum sativum) and Amphicarpaea edgeworthii. The species is thought to normally be holocyclic, although anholocyclic populations are present in warmer areas. It is found in east Asia including east Siberia, China, Taiwan, Japan and Korea. It has recently been introduced to New South Wales in Australia. Other aphids on the same hostMegoura crassicauda has been recorded on 3 vetch species (Lathyrus davidii, Lathyrus japonicus, Lathyrus palustris).
Megoura crassicauda has been recorded on 13 bean species (Vicia amoena, Vicia amurensis, Vicia angustifolia, Vicia cracca, Vicia faba, Vicia flava, Vicia japonica, Vicia megalotropis, Vicia pseudo-orobus, Vicia sativa, Vicia sepium, Vicia unijuga, Vicia venosa).
Megoura crassicauda has also been been recorded on Pisum sativum and Amphicarpaea bracteata ssp. edgeworthii (=Amphicarpaea edgeworthii =Amphicarpaea trisperma, Chinese hog-peanut, which has also been recorded hosting the soybean aphid, Aphis glycines).
Damage and controlMegoura crassicauda is a serious pest in broad beans (Vicia faba) and other leguminous crops in much of Asia. Hales et al (2017) reported its first detection in Australia, on faba bean crops in 2017. High population densities covering the entire stems and basal shoots of infested plants were reported. Hand-spraying with petroleum oil and subsequently imidacloprid (a neonicotinoid) were ineffective in controlling the aphid infestations, and the plant shoots and pods turned black and died. The yield of mature bean pods was almost zero. Natural enemies had no noticeable effect on the number of aphids, possibly because Megoura crassicauda may be toxic to coccinellid larvae. Infestations have since been effectively controlled with pirimicarb (a selective carbamate insecticide), using two sprays per season at least 14 days apart (Duric, 2021). Surprisingly, and in contrast to the earlier observations, Kasai (2016) found that infestation with Megoura crassicauda did not reduce bean production in narrow-leaved vetch (Vicia sativa).
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