Hoplochelus marginalis Fairmaire

White sugar cane worm

General

• Endemic to Madagascar, Hoplochelus marginalis is well known, in Reunion, under the name of "white worm". Its accidental introduction dates back to the 1970s. Identified for the first time in 1981, the white grub has encountered no factor limiting its development and has gradually invaded all the cane-growing areas of Reunion. Its biological cycle lasts 12 months divided into four stages. The white grub can also cause root damage on vegetable crops and berries (salads, strawberries, etc.).

• Sensitive botanical family (s)

• Affected production area :

• Organs attacked

Symptoms, damage

• Symptoms :
  • The damage caused by the white grub is mainly due to the third instar larvae which eat away at the roots of plants. The plant becomes unable to draw normally water and nutrients essential for its development from the soil. There is stopping of growth of the plant, wilting of the foliage and generalized dieback. The symptoms are those of a complete drying out of the leaves, even of the stems when the root system is completely destroyed. White grub damage is also a pathway for secondary diseases.

• Signs  :

• Possible confusion : 

Biology

• Development cycle :
  

  • Stage 1: October to December

    The emergence of the adults from the soil is triggered by the heavy rains in early summer. The beetles come out at dusk, the day after a rain. After mating, the female drops to the ground to lay eggs in the soil near a food source. The laying totals between 40 and 60 eggs deposited in several times. The female can mate again a month later. The flights result in a dispersion of 2 to 4 km and a large number of adults congregate in one place. This semi-gregarious behavior explains the damage by spots in the plots. The flight ends between 7 p.m. and 8 p.m. depending on the length of the days. The adults behave at night and rest during the day in shallow soil. Their digging front legs allow them to dig easily. Their lifespan is 2 to 3 months during which they nibble the leaves of various plants.

   

  • Stage 2: January to February

    The white eggs are a few millimeters in diameter and have a tough shell. They incubate 2 to 3 weeks before hatching. Young larvae will go through 3 stages (L1, L2 and L3). The L1 and L2 stages are not very mobile and feed on organic matter. L1 and L2 larvae measure 0.5 cm and 1.5 cm respectively. After a month and a half, the larva performs a second moult to reach the L3 stage.

   

  • Stage 3: March to August

    The L3 stage, extremely mobile and voracious, attacks the roots without any preference for the host plants. The larva has powerful mandibles that allow it to gnaw and pierce the roots of various plants. Depending on food resources and soil constraints, it can be found at depths ranging from 5 cm for grasses, to 30 cm for sugar cane. It moves easily from root to root to feed and accumulate enough reserves to pupate. After 4 to 5 months of development, it reaches 5 to 6 cm long.

   

  • Stage 4: August to September

    The mature L3 larva then burrows deep into the soil and enters the resting phase. After a final moult, the nymph appears. This immobile incubates 2 to 3 weeks and undergoes important morphological modifications to end up in the chafer. Humidification of the soil by rains allows adults to rise to the surface to take flight. 

   

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  Protection

  • Mechanical control: carry out deep plowing before planting; they bring eggs and larvae to the soil surface where they are predated by ants or birds.

  • choice Variety : varieties with strong root regeneration such as R570 are less affected by attacks.

  • Irrigation : when done well, it allows the plant to better tolerate an attack and a better resumption of root development; in addition, a moist, well-irrigated soil prevents the larvae from moving properly and therefore reaching the roots.

  • Control : the current control system is based on the use of a bio-control agent, an entomopathogen of the genus Beauveria. This entomopathogen is contained in a formulation applicable to soil, BETEL®. Spread of the fungus can also be done by soaking the chafer in a solution Beauveria . Intact adults are captured at nightfall near a light source, soaked in the solution, and then released. They fly away and die a few days later in the soil, spreading the infection in fields and non-agricultural areas.

     

  Since 1995, a prefectural decree imposes control on planting with the use of BETEL® for cane trees at a dose of 30 to 50 kg / ha. Since 2013, this compulsory control has been open to long-cycle market gardening crops.

   

  In 2013, following the appearance of pockets of resurgences in the south of the island, the production of beetle dipping kits was relaunched by the FDGDON. Farmers and individuals can thus participate in the complementary fight against white grub.