Wind dispersal and settling of first-instar crawlers of the cochineal insect Dactylopius austrinus (Homoptera: Coccoidea: Dactylopiidae)

. 1. The efficiency of D.austrinus as a biological control agent depends on successful colonization of the cactus weed Opuntia aurantiaca. 2. Unlike other coccoid insects, the female crawlers (first-instar larvae) of cochineal insects develop long wax fiaments on the dorsal surface of the body that reduce their terminal velocity in air and enhance wind dispersal. 3. Dactylopiid males are dispersed as winged adults and male crawlers of D.austrinus have fewer and shorter filaments than the females and they are blown a shorter distance in a wind tunnel. 4. Vertical and horizontal wind dispersal of D.austrinus from O.aurantiaca in the field is usually very limited, but was greatly improved when crawlers were launched from an elevated ‘tower’. 5. Preparatory to dispersal, female crawlers climb to the top of the host plant and ‘take-off’ from there. This behaviour is most marked in crawlers 2–3 days old at which stage the wax filaments are best developed: the behaviour is never manifest following artificial ‘dispersal’. 6. Final settling on cladodes of the host plant is a function of the age of the female crawlers and of the condition of the cladodes. 7. When given a choice, approximately equal numbers of crawlers settled on cladodes that had received high and low fertilizer treatments. More crawlers settled on cladodes that had been kept in the shade than on those kept in the sun, and on basal rather than terminal cladodes. 8. The highest percentage of crawlers settled on cladodes that were 20% dehydrated. Settling success was much lower on more desiccated cladodes.