M. lareynii populations released in BC originated in Italy via Colorado.
The weevils are 4-5mm long, with brown cylindrical bodies, which widen at their posterior. Their bodies are covered with grey, erect hairs. Their snouts are short and broad. Adults emerge from overwintering locations in the spring and begin feeding on plants. Females prepare oviposition locations by chewing a small pit into the side of a developing seedpod. Young pods are preferred over mature ones. Eggs are deposited singly into the pit and the opening is then sealed with grey-black fecal cement. The pit must be deep enough into the seed covering to ensure the newly hatched larvae will be in direct contact with the enclosed seed chamber. Each female will lay up to 324 eggs. The number of generations depends on the climate. When plants decline, the adults have keen host plant seeking abilities, and take flight as required.
Eggs are dark yellow or pale amber coloured, oval, and measure 0.5mm in length.
The larvae are C-shaped and dirty-yellow coloured. Development occurs within the seedpod through four instars. Assuming conditions are ideal at the time of oviposition, the newly-hatched larvae will attack the seed immediately and in most cases will destroy all the developing seed in one of the five chambers of this plant species seedpods before moving to another. Usually, each larva will use two sections of the spiny five chambered seedpods, and up to three weevils can complete development in a single pod. If eggs are deposited into mature pods, the protective seed coat will have already hardened and the new larvae will be unable to penetrate through it. In this case they will attempt to feed beneath the outer pod layer, but will eventually die. Pupation lasts four to five days and occurs within the pod chamber which is loosely filled with frass. Pupae are creamy white or pale yellow and 4.5mm long. The duration from egg to adult cycle typically takes 25-30 days at 20 to 30°C.
Adults that emerge from pods in August through September overwinter in surface litter.
Location & Efficacy:
The most effective damage is caused by the larvae as they feed on developing seeds. Individual larvae will usually feed within two chambers and will consume all seeds present. Adult feeding on stems, leaves, buds, flowers and fruits have limited effect on the plants' vigour.
Microlarinus lareynii is sensitive to cold weather, limiting its habitat to warm or hot areas. Since its introduction to the USA it has become established in Arizona, California, Colorado, Hawaii, Kansas, New Mexico, Nevada, Oklahoma, Oregon, Texas and Utah. In its native habitat it is common to Eurasia and Africa and is consistently found in India, Rajasthan Desert, Italy and coastal and interior France. It has a wider distribution than M. lypriformis (a stem feeder) as it was found in 1958 at 90% of all sites researched. In BC, M. lareynii has been released into one of the hottest locations in the Bunchgrass biogeoclimatic zone. No establishment has been found at the release location, so habitat preferences cannot be determined.
A single M. lareynii release was made in 1986 in Osoyoos, from a collection taken from what was considered to be the harshest climate in the USA. Repeat visits to the site have indicated no establishment.
Several years after the initial release, the site underwent extensive disturbance, but the plant has regenerated and is now appearing to spread northward. It is not known if the agent failed to establish prior to the excavation. The status of this agent is still being investigated. Monitoring for establishment is ongoing.
When combined with M. lypriformis (stem feeder), M. lareynii can significantly reduce plant vigour.
There are no cold weather biological control agents available for puncturevine in the USA or Canada. Releases made in 1961 and 1963 in south eastern Washington, USA failed to establish and were blamed on harsh winters. Another attempt was made in 1982 with a cold hardy strain from Colorado, but it too has not proven successful. However, the closest known established site to Canada is in Oregon, USA.