Evidence that maize wallaby ear disease is caused by an insect toxin

Abstract

S U M M A R YColonies of the leafhopper Cicadulina bimaculata were established from single male and female insects raised from surface sterilised eggs and shown to be free of leafhopper A virus (LAV). Insects from these colonies were as capable of inducing maize wallaby ear disease (MWED) in maize seedlings as those with LAV indicating that the virus is not involved in the etiology of MWED.Maize seedlings colonised by C. bimaculata in glasshouse trials developed initial MWED symptoms within 6-8 days of infestation. The symptoms intensified thereafter and many plants died after more than 16 days' exposure, even after the insects were killed with insecticide. However, when freed from the insects before symptoms became very severe, plants recovered and assumed normal growth. These observations support the view that MWED is caused by an insect toxin.

Effect of temperature on the development and reproduction of the maize orange leafhopper Cicadulina bipunctata (Melichar) (Homoptera: Cicadellidae)

“…Among these cereals, severe damage by C. bipunctata was reported on maize in several countries such as Australia (Grylls, 1975) and the Philippines (Agati and Calica, 1949;Maramorosch et al, 1961). Previous studies attributed this damage to a leafhopper-transmitted virus (Agati and Calica, 1949;Maramorosch et al, 1961;Grylls, 1975;Reddy et al, 1976;Boccardo et al, 1980), however, recent studies suggest that chemicals injected by C. bipunctata while feeding are responsible (e.g., Ofori and Francki, 1983;Ohata, 1993;Kawano, 1994). Therefore the damage is considered a sort of insect gall, but the mechanism inducing this response is still unknown.…”

Ecology of the Maize Orange Leafhopper, Cicadulina bipunctata (Melichar) (Hemiptera: Cicadellidae)

“…As mentioned above, MWES is caused by chemical(s) from C. bipunctata 22 . Upheaval of leaf veins appears not on leaves that are infested by C. bipunctata but on those that emerge during or after infestation 12 .…”

“…This symptom is characterized by stunted growth together with severe swelling of leaf veins 12,22 and has threatened maize production in these areas due to substantially reduced yields. Because MWES superficially resembles symptoms caused by viral pathogens, it was initially identified as a viral disease transmitted by the maize orange leafhopper, Cicadulina bipunctata (Melichar) 1 .…”

“…Because MWES superficially resembles symptoms caused by viral pathogens, it was initially identified as a viral disease transmitted by the maize orange leafhopper, Cicadulina bipunctata (Melichar) 1 . More recent experiments indicated that MWES is caused not by a virus but by chemical(s) injected by C. bipunctata during feeding activity 12,22 . In Japan, MWES has been a serious concern since 2000 in Kyushu island, the most southern of the four main islands of Japan.…”

Distribution, host plants, and seasonal occurrence of the maize orange leafhopper, Cicadulina bipunctata (Melichar) (Homoptera: Cicadellidae), in Japan

“…The gall symptom was previously suspected to be caused by a viral disease referred to as maize wallaby ear disease (Maramorosch et al, 1961;Grylls, 1975); however, the galls are now regarded as insect galls produced in response to the injection of chemicals by C. bipunctata during feeding (e.g. Ofori and Francki, 1983). The condition is therefore now called "maize wallaby ear symptom" (MWES) .…”