Characterization of the Induction of Stress Ethylene Synthesis in Cotton Caused by the Cotton Fleahopper (Hemiptera: Miridae) and Its Microorganisms

Abstract

The cotton fleahopper, Pseudatomoscelis seriatus (Reuter), induced stress ethylene production by detached, vegetative shoot tips of young cotton, Gossypium hirsutum L., plants. Ethylene production rates reached abscission-inducing levels within 24 h or less and remained well in excess of the threshold levels for 3 d. Among the microorganisms associated with the fleahopper, the two most common Fusarium spp. were identified as F. semitectum Berk, and Ravenel and F. equiseti (Corda) Sacc. Ethylene production followed a similar pattern in both insect-infested and F. semitectum -inoculated shoot tips, but the peak rate occurred earlier with F. semitectum inoculation. Field-collected insects, laboratory-hatched insects, insects collected immediately after molting, intact eggs, and ruptured eggs all were almost universally contaminated with microorganisms. Under extended storage of stems containing overwintering fleahopper eggs, the number of insects hatching per stem, the degree of contamination of the insects that hatched, and the capacity of these insects to cause stress ethylene production all decreased. Our data are consistent with the hypothesis that microorganisms are involved in the symptoms of fleahopper injury to cotton—inhibited internode elongation and abscission of young flower buds. This suggests that stress ethylene causes the symptoms, and that some of the microbes may be disease organisms; if so, the insect is a vector. The involvement of microorganisms in injury does not eliminate the possibility that other mechanisms may also be involved.