Foraging and egg-laying behaviour of the coccinellid predator Rhyzobius lophanthae

Abstract: The coccinellid beetle Rhyzobius lophanthae Blaisdell (Coleoptera: Coccinellidae) is a specialist predator of diaspidid scale insects. In a greenhouse experiment, it was tested whether a) Rhyzobius provides better control of Diaspis boisduvalii scales when introduced in the scale-infested plant than when released elsewhere in the greenhouse, b) the level of control depends on the size of the scale-infested area and c) the control of small- to medium sized scale colonies by R. lophanthae could be stimulated through the addition of Ephestia kuehniella eggs in the scale-infested area. Rhyzobius lophanthae quickly located almost all of the scale-infested plants to which they had not been released, and the level of control was independent of the release site. Medium- and large-sized scale colonies were more effectively controlled by R. lophanthae than small-sized scale colonies. The addition of E. kuehniella eggs improved the level of control in small-sized scale colonies, but not in medium-sized scale colonies. Moreover, in additional laboratory experiments it was found that R. lophanthae was able to survive well on a number of alternative food sources, and that they maintained their ability to lay eggs under the shields of D. boisduvalii scales after a period of 4 weeks on alternative food.