The etiology of damage to lucerne by the green mirid, Creontiades dilutus (Stal)

Abstract

Green mirid [Creontiades dilutus (Stsl) (Miridae: HEM)] of all developmental stages was found in lucerne throughout December and January 1989-90 at sites near Adelaide, Australia. In the laboratory, they were unable to complete development when given foliage only, but 65% completed development when provided with flowers, from which they fed preferentially on the developing ovules. Only 25% developed from egg to third instar when cut pods were the sole food source but all survivors completed their development on pods thereafter. The insects were observed to make unsuccessful attempts to feed on spotted alfalfa aphid [Therioaphis trifolii (Monell) f. maculata Aphidae (HEM)]. When fifth instars were caged on entire plants, most of the insects were subsequently found near the tops of the plants. Ten adults caged on a head with 7 pods caused them to turn yellow in 5 days, brown in 6, and withered in 7. An adult caged with 2 flowers for 5 h caused both to drop the standard petal and to abort development within the subsequent 24 h. Feeding frequency of fifth instars when given flower heads ad libitum was estimated at 18 times, for a total of 169 minutes, over a 5-h observational period. The saliva contained a pectin, endopolygalacturonase, and its injection into developing ovules and seeds probably accounts for the etiology of damage. The insects' requirement of lucerne seeds and/or ovules to complete its development, its frequency of feeding, and the abscission of whole flowers due to feeding on the ovules probably accounts for the serious losses of seed production previously reported.