Insect Pathogensand Insect Parasitic Nematodes IOBC/wprs Bulletin Vol. 45, 2009
pp. 457-460
Optimised protocol for wireworm rearing
Ursula Kölliker, Werner Jossi, Stefan Kuske
Agroscope Reckenholz-Tänikon Research Station ART, Reckenholzstrasse 191, CH-8046 Zürich, Switzerland
Abstract: Wireworms for bioassays are usually collected in the field. This can be quite tedious since wireworm infested fields may be difficult to be found and wireworm infestations can be difficult to predict. An optimised protocol has been developed to rear wireworms of the species Agriotes obscurus, A. lineatus and A. sputator in the glasshouse. Adults are collected in the field in May and transferred to plant pots in the glasshouse for egg laying at 20 to 25°C. In January, 20 to 200 larvae large enough to be used in bioassays may be retrieved per pot. Each May the rearing is restarted by collecting adults in the field. Using this method, a sufficient number of larvae can be produced for bioassays with limited effort and without having to rely on field collections.
Key words: Wireworms, click beetles, Agriotes, culture, rearing
Introduction
When performing bioassays with wireworms of Agriotes spp., one of the basic questions is where to get these insects from. Usually the larvae are collected in the field. Collecting wireworms in the field for use in bioassays can be quite tedious, cumbersome, tricky and frustrating. Wireworms live in the soil and infestations are difficult to predict. One year there may be a heavy infestation and the next hardly any wireworms can be found in the same field.
Even in infested fields, it may still be difficult to catch sufficient numbers of wireworms as their presence may be very patchy within the field. Since it takes the larvae several years to develop into adults, field populations consist of larvae at different developmental stages, while for bioassays larvae of similar age have to be used. In addition, larvae of the different Agriotes species are very difficult to distinguish and larvae from field collections may belang
to different species. Also field collected wireworms may be infected by pathogens.
Rearing wireworms from adults may offer an alternative to wireworm collection in the field. Adults are collected in spring, brought to the glasshouse and put in plant pots where they lay eggs. Then the hatching larvae are reared up to the developmental stage required for bioassays. Rearing wireworms in the glasshouse overcomes the problems encountered when collecting wireworms in the field.
Optimised protocol
Wireworms of the species Agriotes obscurus, A. lineatus and A. sputator are cultured in the glasshouse at 20 to 25°C in plant pots with a diameter of 30 cm filled with 10-15 L sterile soil rich in humus. The holes at the bottarn of the pots are sealed with mesh screen so that water can go through but the wireworms stay inside the pot. Wireworms are fed by sowing a mixture of Festuca rubra, F. pratensis, Poa pratensis and Lolium perenne into the pots. Then the pots are covered with a mesh screen bag.
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Collecting adult click beetles in spring represents the main work Ioad. At the end of April plastic sheets ( 40 x 40 cm) are placed on bare soil on agriculture farmland ( eg. between rows of maize or beets). Adults can also be collected from natural meadows where wireworm infestations are expected. There the sheets are placed on the freshly cut grass. The sheets are then covered with fresh grass. On the following moming beetles aggregated between the grass
and the plastic sheet are collected (Fig. 1 ).
Figure 1. Adults collected from plastic sheets in a meadow
Most click beetles are found when the weather is warm and humid. After collecting click beetles from the field, they are kept in plastic containers for 24 hours and fed with a honey/yeast (9: 1) mixture (Fig. 2).
Figure 2. After collecting adults in the field, they are kept in plastic containers for 24 hours and fed with a honey/yeast mixture
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Then the click beetles are transferred to the glasshouse. Per plant pot, 20-30 adults are placed into the mesh screen bag for egglaying (Fig. 3). A funnel is used to insert the adults
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into the mesh screen bag. Adults in the mesh screen bag are fed using the honey/yeast mixture. The mixture is smired onto the mesh screen ba and renewed once to twice weekly.
Figure 3. Plant pots covered with a mesh screen bag into which the adult click beetles are released
At the end of June the egg laying period is finished and the mesh screen bag is removed.
The grassmixture is ilnmediately resown, providing food for the hatched larvae. The young larvae like to feed on germinating seeds. As the soil needs to stay moist the plant pots are watered three times per week. By observing how well the grass grows allows to predict the development of larvae in the plant pots. If there is hardly any grass growing in the pot, there will be a large nutnber of larvae feeding on the roots of the grasses in the pot. On the other hand ifthe grass is growing well, then there won't be many larvae in the pot. From the middle of August onwards, wheat or oat is used to resow the pots twice per month (Fig. 4 ).
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Figure 4. Wireworms reared in plant pots in the glasshouse. Bare pots indicate the presence of larvae that feed on the germinating seeds. Pots covered with grass won't contain many larvae
In January the wireworms will be large enough for use in bioassays. A. sputator is developing faster than the other two species. The size of the larvae may need tobe checked towards the end of the year and if necessary the larvae are transferred to a cool room (1 0°C) to slow down the development. Some pots may have to be discarded due to wireworms infected with entomopathogenic fungi, especially vvhen rearing susceptible species like A. obscurus.
The number of wireworms developing per pot varies a lot. At the beginning of the year 20 to 200 individuals may be retrieved per pot.
Conclusion
By using this method, a sufficient number of larvae of a certain species and a similar age can be produced for bioassays with limited effort and without having to rely on field collections .
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