Phyllopertha horticola (Coleoptera: Scarabaeidae)
Identifying different life stages
Across Europe several species of turf chafer beetle can be found. These have variations in lifecycle and susceptibility to beneficial nematodes. The most common turf grub species is the garden chafer (Phyllopertha horticola). Garden chafer undergo complete metamorphosis passing through distinct egg, larvae, pupae and adult stages.
Eggs are small, spherical, and pearly white approximately 0.5 mm in size. They darken just before hatching having swollen through water absorption to 2-2.7mm.
The white grub or larvae have white bodies that range from 4 mm when newly hatched to 18 mm when mature (Figure 1). The grubs have six legs, a dark brown head capsule and normally curl their bodies into a characteristic "C" shape. The different species of turf grubs can be differentiated by their raster arrangement (Figure 2).
Pupae are about 16mm long. They are coloured white, faint yellow or dark brown.
Adult garden chafer beetles are 9 to 11 mm long. They have a metallic green head and thorax with light brown wing cases (Figure 3).
Garden chafers (Phyllopertha horticola) have a one year lifecycle.
Adult swarming occurs a few hours before noon from the end of May to mid June. After mating females return to the soil where they lay eggs in crevices at a depth of 4cm though this may be as much as 20cm where the soil depth allows. Females lay 80% of the eggs soon after mating. Due to the laying of the majority of eggs very early, controlling the adult beetles does little to affect the number of eggs laid and the eventual size of the population. More eggs are laid after feeding at distances as far as 4 km from the point where the adult emerged. Eggs hatch 4-6 weeks after laying. Upon hatching the first larval stage lives close to the soil surface in the top 4cm. Through the autumn the larvae pass through two more larval life-stages. All larvae feed on the roots of the grass. The first stage feeds on dead organic matter along with small roots. The second stage will feed on larger roots. The third stage larva is the stage which feeds the most. This is in order to build-up enough fat reserves to hibernate through the winter and will consume main roots of grasses. In late October when soil temperatures start to fall the larvae migrate deeper into the soil in order to escape the cold soil temperatures and ground frosts through winter. This can be as little as 5 cm deep in shallow soil or as much as 30cm in deeper soils. Larvae then return to near the soil surface to pupate in spring when soil temperatures increase. Pupation occurs over 4-5 weeks before adults emerge. Adult beetles feed on leaves and flowers of deciduous trees, often located around the edges of turfed areas. Adults are able to fly, so are able to move between their food source in nearby woodland and the turf where oviposition takes place. Repeated returning to the same area by adults laying eggs can mean that the problem will get progressively worse year after year.
Damage to turf is caused by all larvae stages of garden chafer. Unless very high pest populations are present, the most noticeable damage is caused by the final larval stage due to its increased level of feeding on turf roots to prepare for hibernation.
Adults can cause damage to deciduous tree crops such as orchards through feeding on leaves and flowers. However, this is rarely of economical importance.
Adult garden chafer swarming can be observed between the short window from the end of May to mid-June. The adult forms of different chafer species are easily distinguishable. Egg laying will take place on turf, adults can be found resting in overgrown areas around the turf or in nearby woodland.
Larvae are found in the ground beneath managed turf. Larvae can be found close to the soil surface from late July to late October.
Chafers are common across Europe with the species of chafer causing the problems dependent on the region. The garden chafer (Phyllopertha horticola), is the species most likely to infest turf in Europe. Other examples are the Welsh chafer (Hoplia philanthus) which is commonly found on sandy soils. The cockchafer, or may bug (Melolontha melolontha), the largest chafer at up to 30mm long. Summer chafer (Amphimallon solstitiale) are also common throughout Europe. For these other turf grub species, their life cycle is completed over two or three years.
Larvae feeding will occur from July to early November. Larvae feeding on the plant root system will stop when temperatures fall and the larvae move deeper into the soil to avoid the cold winter. When this movement occurs will vary depending on geographical location. Typical high risk periods for seeing turf damage are September and October when the larger larvae consume more grass roots.
Adult feeding will occur through late June and into July. It is rarely noticeable.
The first larval stage feeds on dead organic matter and small grass roots in the soil at 5 to 10 cm depth, the second stage larvae feed on progressively bigger roots. Most damage is caused by the third stage larvae. They have the greatest capacity to feed in preparation for hibernation and are capable of eating the main grass roots severing the water supply and killing the plant. It is at this time that the major discoloration of turf grass is seen.
Chafer larvae larval feeding is the primary cause of damage to turf grass. Damage shows as yellow patches of turf due to stress where the reduced root mass is no longer able to supply the grass with the water and nutrients it requires. This grass is easily pulled up like carpet due to the lack of root system (Figure 4).
More obvious symptoms are a result of the secondary damage from scavenging predators such as crows and badgers. This is often worse than the primary damage. These predators dig up the loose turf in order to feed on the larvae beneath. Bird feeding results in distinct patches of pulled up small tufts of grass (Figure 5). Feeding by mammals results in destruction of great areas of turf (Figure 6).
With the symptoms of both leatherjackets and garden chafer grubs being similar, examination will help determine the cause of the problem.
All types of turf grasses are susceptible. Damage is most noticeable in highly managed sports turf.
Nemasys®G is based on the beneficial nematode Heterohabditis bacteriophora and provides a rapid curative control of the larval stages of the Garden Chafer Grubs (Phyllopertha horticola) in turf.
Nemasys®G contains nematodes in their vigorously infective juvenile stage. These aggressive organisms actively seek out the Garden Chafer larvae and enter them through their natural openings. Once inside the larvae they release symbiotic bacteria, quickly killing the insect pest. The nematodes then reproduce inside the insect and release a new generation of infective juveniles which disperse in search of further larvae.
Nemasys®G is a curative control and therefore can be targeted exactly where the larvae are present and where the secondary damage from birds or mammals is the occur