Vine Weevil Description
The adult beetle is flightless, it is dark brown or black in colour and has fine yellow speckles on its back, and appears dusty. The adult is nocturnal so rarely seen during the day.
Most commonly found are the larvae (grubs), these are found in soil or compost around the roots of plants. The larvae are creamy-white in colour with a brown head, they curl into a “C” shape when touched. Pupae may also be found amongst the plant roots. These are also creamy-white in colour but have started to produce legs and antennae.
Vine Weevil Damage
Adults feed on the edges of leaves during the summer, generally April to August, causing notching. The beetles walk and climb exceedingly well, making plants in hanging baskets and wall boxes easy prey.
The eggs laid throughout the summer develop into larvae (grubs) which feed on plant roots, this is the stage in which the insect causes most damage.
Symptoms range from lack of growth, dying leaves or branches right through to sudden wilting and death. The latter case being seen when plants have single tap roots or have been attacked at the main stem.
Grubs can also bore into corms and either kill by eating the inside away or by allowing infection to enter and cause rot.
Vine Weevil Life Cycle
All vine weevil are female, and so all adults are capable of laying eggs. The adults are nocturnal, hiding during the day at the base of plants, under plant pots or hidden in debris. They can often be found inside houses.
The adults lay their eggs around the base of a plant, each adult will lay on average 500-600 eggs throughout the summer, although as many as 1,500 has been recorded.
Newly laid eggs are white turning brown as they mature. Potentially 40% of eggs can make it to the larval stage although dry or very wet soil conditions will take their toll.
The eggs take between 8.4 days at 27ºC and 56 days at 9ºC to hatch into larvae. At this stage the larvae are about 1mm in length, creamy white with a dark head. Eventually these grubs can grow up to 13mm in length after feeding.
When the grubs are fully grown they burrow 15-20cm into the soil to pupate before hatching as adults.
In warm greenhouses, all stages of the vine weevil can be found at any time. Outside, in pots and containers, the adults usually start to hatch in April, this can be earlier in warmer years.
The adults feed throughout the summer, lay eggs from late August and die out during the autumn. The grubs in the soil then over-winter before pupating and hatching in the spring.
Biological Control of Vine Weevil
Vine weevil can be controlled biologically by using their natural enemy, the parasitic nematode, Steinernema kraussei also known as Nemasys.