Lady beetle

Stethorus punctillum

Stethorus punctillum is native to Europe, but is now widely distributed throughout temperate North America and Asia. This species is a specialist predator of mites, with a global host range that encompasses 14 different species, including two-spotted spider mite (Tetranychus urticae), spruce spider mite (Oligonychas ununguis), Southern red mite (Oligonychus ilicis) and European red mite (Panonychus ulmi).

The adult beetles are black and oval in shape, approx, 1-1.5 mm long, with yellowish legs and antennae. Under magnification, short, fine hairs can be seen covering the wing cases (elytra). The four larval stages are olive-grey to dark brown, with paler hairs on the sides of each segment; pupae are dark-colored, oval in shape. and covered with numerous setae. Both the adults and all four larval stages are predatory, and will generally attack all prey life-stages.

The optimum temperature for S.punctillum survival is approx. 25°C (77°F), but it can be effective at temperatures of 20-30°C (68—86°F). It also tolerates a wide range of relative humidities (approx. 40-90%) and can be a useful complement to predatory mites, particularly as the adult beetles have good dispersal abilities and can actively seek out developing ‘hot spots’ of pest mites.

Newly emerged adult females must feed for approx. 1 week before egg-laying can begin, and need at least 20 spider mites per day to both commence and sustain egg production. When prey is abundant, adult females may produce up to 13 eggs per day, and under glasshouse conditions may live approx. 30-70 days (depending on temperature and prey) . Both egg production and longevity are generally higher under outdoor conditions. Eggs are laid singly, close to spider mite colonies (on the underside of leaves). Mature larvae tend to move toward the base of the plant to pupate, fixing themselves to the underside of leaves or to similar sheltered sites. At 24°C (75°F), the life-cycle (egg to adult) is completed in approx. 17 days.

Note that this species is sensitive to a variety of pesticides, which can disrupt development.
The effectiveness of S. punctillum also tends to be reduced on plants with glandular or hooked trichomes (e.g. tomato and various Phaseolus beans).