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Tracking the red palm weevil

Microchips to monitor the movements of a pest insect

Charançon rouge du palmier, Rhynchophorus ferrugineus, équipé d’une puce électronique de type RFID (en anglais radio frequency identification) décelable à courte distance (10 cm).. © INRA, Rachid Hamidi
Updated on 06/15/2017
Published on 01/24/2017

Originating from Asia, the red palm weevil, Rhynchophorus ferrugineus, is a much feared pest. Its larvae devour palm trees from the inside – mainly date palms in the Middle East, ornamental palms in Europe – causing their inevitable death. It is vital to understand how this insect travels in order to estimate, and above all manage, the risk it represents, but there remains a dearth of data on this issue.

INRA scientists in Versailles-Grignon decided to take advantage of a recent and promising technology, radiolabelling, in order to gain a more detailed understanding of the movements of this weevil, both in the palms where it lives most of the time, hidden in its numerous crevices, or nearby when it leaves and spreads.

Easy to say, but much more difficult to achieve!

Indestructible devices…

The scientists first of all assessed the resistance against the burrowing behaviour of this insect of two devices: radio frequency identification (RFID) microchips that can be detected at short distances (10 cm), and radio transmitters equipped with an aerial and micro-battery detectable at longer distances (>50 m according to the manufacturer). They fixed the chips to the thorax of insects and thus labelled left them in a contained space under conditions similar to their natural environment.

One week later, almost all the devices (90%) were still in place. The RFID chips were all intact, but not the radio transmitters, where the majority of their aerials (90%) were damaged, thus markedly reducing their ability to be detected at any distance.

… without effects on the behaviour of the insects

The presence of RFID chips did not affect the flight capacity of the insects. However, although the radio transmitters allowed all the insects to fly, normal flight behaviour was only possible in 17% of them, the others being visibly distressed by the weight of the device.

Boosted by these initial findings, the scientists decided to use the RFID chips for their experiments. Their detection and localisation of invisible insects – because they were living inside the palm trees – proved simple, and almost without interference when two insects came into contact. Furthermore, these chips affected neither coupling nor laying.

These encouraging results offer interesting perspectives regarding study of the behaviour of red palm weevils. In the longer term, the use of RFID chips could enable a precise picture of the grouping or dispersal dynamics of this insect, in order to better assess and manage the risk it represents.

The weevil and the chip, in practice

The 77 red palm weevils used during this study (38 males and 39 females) were subjected to a temperature of 27°C, humidity close to 70%, a photoperiod alternating 13 hours of light and 11 hours of darkness. Reared in the laboratory, the insects were 15 days old at the time of the experiments. Correctly contained in a quarantine facility, the adult insects were fed with fresh sugar cane and the larvae with an appropriate nutrient solution.  

The chips – RFID or radio transmitter – were fixed to the dorsal surface of the thorax of the insects, where the surface of the carapace had previously been roughened using fine sandpaper so as to ensure good adhesion of the glue.

The RFID chips had an average weight of 32.9 mg and were 8.4 x 1 mm in size, while the radio transmitters weighed 170 mg for a size of 8 x 4 x 2 mm plus the aerial, which was 150 mm long.  It should be remembered that an adult red palm weevil is on average 35 mm long (not including the rostrum) and 12 mm wide, weighing 800 mg.

On the subject of

Hamidi R., Couzi P., Khfif K., Rochat D. (2016) Impact of active and passive radio tags on the flying and burrowing behavior of the red palm weevil, Rhynchophorus ferrugineus (Coleoptera: Dryophthoridae). Appl. Entomol. Zool. DOI:10.1007/s13355-016-0464-x