Scarabaeidae (scarab grubs)

Commonly referred to as white grubs, root-feeding larvae (Fig. 9-1) of members of this family are among the most damaging pests of tall fescue pasture, and turfgrass in parts of the United States (Tashiro, 1987; Potter, and Braman, 1991), Australia, and New Zealand (Table 9-1).


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Fig. 9-1. Asiatic garden beetle larva, Maladera castanea (photo: Fred Baxendale).


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Table 9-1. Major Coleopteran pests of tall fescue in the United States, Australia, and New Zealand.


The majority of species are univoltine (i.e., have an annual lifecycle), and adults either do not feed at all or feed on foliage of a range of tree species. Adults of the African black beetle (Heteronychus arator) (Fig. 9-2), a serious pest of grasses in parts of New Zealand and Australia, are an exception because they feed on tillers of their gramineous hosts. The subterranean habits of scarab larvae make them particularly difficult to control. Larval damage mostly occurs in late summer and early winter when dead and dying patches of grass appear as manifestations of root feeding (Fig. 9-3). In New Zealand, tall fescue is a favorable host of Costelytra zealandica, a native insect that has adapted well to improved pasture grasses. Tall fescue can support high densities of these grubs but is more tolerant of larval feeding than perennial ryegrass because of its more extensive root system (Kain and Atkinson, 1977; Kain et al., 1978; East et al., 1980). Nevertheless tall fescue is not immune to damage from white grubs, particularly in turfgrass systems or when the effects of root feeding are exacerbated by dry conditions. Both Japanese beetle (Popillia japonica) (Fig. 9-4) and the southern masked chafer (Cyclocephala lurida) (Fig. 9-5) can be destructive pests of a range of grasses including tall fescue (Potter et al., 1992). The European chafer (Rhizotrogus majalis) also can damage cool season turfgrasses in the United States when larvae feed on roots from August to November, and again from March to May, although tall fescue is relatively tolerant of damage (Bughrara et al., 2003). Irrigation and N fertilization may alleviate white grub damage (Potter, 1982; Prestidge and East, 1984; Crutchfield et al., 1995) and, at least in forage systems, is a more economically viable form of control than use of insecticide.


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Fig. 9-2. Black beetle, Heteronychus arator and differences in larval damage to endophyte free (left) and endophyte infected (right) tall fescue (photos: AgResearch).


Fig. 9-3. Typical white grub damage, Scarabaeidae (photo: Fred Baxendale).




Fig. 9-4. Japanese beetle, Popillia japonica. Left: Japanese beetle and eggs (photo: Fred Baxendale); right: mating cluster (photo: Doug Richmond).



Fig. 9-5 Southern masked chafer beetle, Cyclocephala lurida (photo: Fred Baxendale).  



Not all scarab grubs cause damage by root feeding. In Australia and New Zealand, black-headed cockchafer (Aphodius tasmaniae) larvae (Fig. 9-6) live in tunnels underground but emerge to graze on grasses, including tall fescue. Green June beetle (Cotinis nitida) (Fig. 9-7), a species native to the eastern half of the United States, is an important pest of pastures, hayfields, lawns, and golf courses (Hellman, 1995). Larvae feed on organic matter and damage plants by their digging habits, which disrupt the soil-surface interface and reduce the ability of plant roots to access water. The addition of organic matter in the form of organic fertilizers, mulch, grass clippings, poultry litter, cow manure, or composted sewage sludge increases oviposition by the adults and also attracts the mobile larvae, thereby exacerbating the problem (Brandhorst-Hubbard et al., 2001).


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Fig. 9-6 Cockchafers, Adoryphorus spp. Left: red-headed larvae, A. couloni; right: A. tasmaniae larval damage in Australia (photos: AgResearch).



Fig. 9-7 Green June beetle, Cotinus nitida (photo: Fred Baxendale).

Effect of Endophyte

Adult African black beetles that feed on tillers are deterred by Neotyphodium endophytes that infect tall fescue (Ball et al., 1994; Popay et al., 2005). Deterrence of the adult affects the location of oviposition and hence the amount of larval damage to the pasture (Fig. 9-2). Where adults do not feed on their gramineous host, as is the case for most scarabs, any effect of endophyte on the larvae must be mediated through alkaloids in the roots. Effects of endophyte infection in tall fescue on survival and weight gain of white grubs in greenhouse studies have been demonstrated (Potter et al., 1992; Popay et al., 1993; Koppenhofer et al., 2003). In rooting boxes, endophyte infected (E+) tall fescue appeared to have a greater tolerance to herbivory by C. lurida (Crutchfield and Potter, 1995). On the other hand, Richmond et al. (2004) found herbivory by P. japonica in monocultures of tall fescue did not differentially affect E+ and endophyte free (E-) tall fescue, although endophyte infection did enhance plant growth.

The loline alkaloids (see Chapter 13) produced by N. coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin, which occur in roots in variable quantities, deter larval feeding (Patterson et al., 1991; Popay and Lane, 2001). In the field, however, clear evidence of effects of endophyte on scarab larvae has been difficult to obtain. Murphy et al. (1993) found fewer white grubs in E+ than in E- tall fescue plots in one of two field trials, but in several other trials E+ tall fescue exerted no measurable effect on larval populations of Japanese beetle (P. japonica) (Oliver et al., 1990; Potter et al., 1992; Davidson and Potter, 1995).


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