Of the pests that feed on macadamia in South Africa, stinkbugs are the most important. The green stinkbug, Nezara viridula (L.) and more than 30 other stinkbug species attack the flowers and developing nuts. This may result in extensive flower and fruit drop of small macadamia fruit and sunken lesions on kernels of mature nuts. If stinkbugs are not controlled chemically, a crop loss of up to 80 % may result. The larvae of the nut borers, the false codling moth, Cryptophlebia leucotreta Meyr., the litchi moth, Cryptophlebia peltastica Meyr., and the carob moth, Spectrobates ceratoniae (Zeller), feed between the green husk and the brown shell, sometimes penetrating the latter and destroying the kernel. Other pests of minor importance include the citrus thrips, Scirtothrips aurantii (Sign.), cotton aphid, Aphis gossypii Gover, plum slug, Latoia latistriga (Walk.) and the mealybugs, Pseudococcus longispinus (T.T.) and Nipaecoccus vastator (Mask.).
The macadamia industry in South Africa is still relatively young, but expanding. With about 2 700 ha under this crop nearly 1 300 metric tons of kernels are produced annually. The most important pests of macadamia in South Africa namely stinkbugs and nut borers damage the nut kernels (Bruwer, 1992; De Villiers, 1993a). Natural enemies of these pests are often not able to keep them below the economic threshold levels. If stinkbugs are not controlled chemically, a crop loss of up to 80% may occur. Cracking and sorting nuts that are badly damaged is very costly and they may be rejected at the cracking mills.
Minor insect pests are often present in macadamia trees but damage is seldom caused (De Villiers, 1993b) .
Stinkbugs (Hem.: Pentatomidae 8 Coreidae)
Stinkbugs are the most important pests of macadamias in South Africa. Damage is caused by a complex of more than 30 different species. In order of importance, the stinkbugs are the Pentatomids Bathycoelia natalicola Distant, Farnva sp., two Nezara spp ., Bathycoelia rodhaini Scouteden, Nezara viridula ( L . ), Nezara pallidoconspersa and the coreid Pseudotheraptus wayi Brown (Bruwer, 1992).
Stinkbugs cause flower drop during bloom, fruit drop before shell hardening and damaged kernels from before to after shell hardening (Bruwer, 1992). Because of the economic implications of the damage caused by stinkbugs, control may be necessary from flowering until harvest.
Damage to macadamia is caused when the stinkbugs suck sap from flowers and
fruit. The adult, N. viridula live and breed for several months, completing about three generations per year (Van oen Berg & De Villiers, 1987). They overwinter as adults.
To try and establish biological control of Nezara viridula and possibly some of the other pentatomids too, the following work was done. Two races of the egg parasitoid, Trissolcus basalis (Wollaston) (Hym.: Scelionidae) were introduced and established in South Africa (Bruwer, 1 987a) . Introductions of Trichopoda pennipes (F.) (Dipt.: Tachinidae) started in 1979 but was unsuccessful (De Villiers et al., 1980) . Later attempts were made to establish T. pennipes in 1994 (Farinelli et al., 1994; Van den Berg, 1994) and in 1995 (Van den Berg, unpublished data). The success of this work still needs to be confirmed.
Two monitoring systems have been developed to estimate stinkbug numbers. The first is a sequential sampling method (Bruwer, 1987b). The lower four branches of 10 (or more) macadamia trees are shaken early in the morning. When the economic threshold of 0,7 stinkbugs per tree is breached, control is necessary. This process is repeated every fourth week (Bruwer, 1987b). In the second method (Froneman & De Villiers, 1991), stinkbugs are sampled by spraying 10 trees with dichlorvos at 150 mB/1002 water. If 12 or more stinkbugs drop from the 10 trees, chemical control is necessary. Monitoring should be done fortnightly.
If control is necessary shortly after flowering and up to the stage when nuts are marble size, spraying with cypermethrin EC 200 g/# at 20 mB/100 2 water is recommended. A second and third application of cypermethrin may be necessary from 4 to 12 and 8 to 24 weeks later. If further spraying is required, endosulfan can be applied at 120 mB/100 2 water. This can be repeated up to 10 days before harvest (Nel et al ., 1993) .
Nut borers (Lep.: Eucosmidae 8 Phycitidae)
Larvae of the eucosmids, the false codling moth, Cryptophlebia leucotreta Meyrick and the litchi moth, Cryptophlebia peltastica Meyrick and the phycitid carob moth, Spectrobates ceratoniae (Zeller) often burrow into the green husk of macadamia fruit and occasionally through the nut shell to feed on the kernel (De Villiers, 1993a). The false codling moth is an important pest in southern Africa, attacking citrus, guava, macadamia, pecan, litchi and many other cultivated and wild fruits (De Villiers et al., 1987). It breeds throughout the year with no liberating phase. It develops in a succession of hosts, commencing in spring, reaching large population numbers in late summer, declining again in winter. Wild hosts contribute to the population increases, often bridging periods during which cultivated host fruits are not at a suitable stage for larval development.
The litchi moth attacks litchi, macadamia, some Acacia spp:, Bauhinia spp. and some other legume trees (De Villiers et a/., 1987).
The carob moth is common in the pods of the carob tree and also breeds in citrus, macadamia, walnuts, acorns, and wild plums (De Villiers et al., 1987)
Control of the nut borers is difficult. Egg parasitoids are present but they are not sufficiently effective especially early in the season. To reduce the numbers of the nut borers, sanitation in macadamia orchards is important (De Villiers etal., 1987). Collect and destroy unusable dropped nuts and husks regularly. No insecticides are at present registered for their control but, treatments to control stinkbugs will also reduce their numbers.
Pests of minor importance
The following pests of minor importance often occur on macadamia trees (De Villiers, 1993b). Except where mentioned, no chemicals are registered for their control .
Mealybugs (Hem.: Pseudococcidae)
The long-tailed mealybug, Pseudococcus longispinus (T.T.) and the Karoo thorn mealybug, Nipaecoccus vastator (Mask.) may occasionally be found on macadamias. Heavy infestations can cause curling of leaves and malformation of branches and nuts. This usually occurs when the natural balance between the pest and their natural enemies is upset by excessive spraying or the use of wide spectrum insecticides. Natural enemies will again control the mealybugs after the effect of the insecticide is canceled.
Generally populations of these mealybugs reach a maximum in spring, after which numbers are reduced by natural enemies. If the latter are rendered ineffective by ants or pesticides, maximum numbers are reached in late summer and autumn. At least three overlapping generations occur per year.
Citrus thrips, Scirtothrips aurantii Faure (Thys.: Thripidae)
The citrus thrips is a serious pest of citrus. It also occurs on macadamia, mango and nearly 100 other hosts, including wild plants. Thrips feed on the ventral side of developing leaves, causing slender malformed leaves with curled up edges. This is occasionally a problem in nurseries but control is seldom necessary. Thrips also feed on green nuts and cause them to turn brown but, this is of no economic importance .
Cotton aphid, Aphis gossypii Glover (Hem.: Aphididae)
The cotton aphid attacks the flowers and the very young leaves, and may occasionally occur in large numbers. Their occurrence are correlated directly with flowering and with growth flushes of the trees. The natural enemies of the cotton aphid include a parasitoid, various ladybirds, hover flies and a lacewing which are usually able to keep the cotton aphid population at low levels.
Bark borer, Salagena sp. (Lep.: Metarbelidae)
The larvae of the bark borer feed on the bark and wood of many different species of trees. Macadamia branches may die as a result of ringbarking but infested trees do not die. The Parasitic wasps usually exert some controlling effect. Infestation sites can be cut out or, according to Nel et al. (1993), larvae feed under a tunnel of silk and excreta. Cabaryl may be sprayed onto the tunnels of silk and excreta for their control.
Plum slug, Latoia latistriga (Walker) (Lep.: Limacodidae)
The larvae of the plum slug feed on leaves of many species of trees and is occasionally encountered on macadamias. The young larvae chew away leaf tissue from the underside, leaving only the upper epidermis. Other larvae feed from the edges of the leaves. Two broods of larvae may occur per year. (Larvae are parasitised by a Tachina sp. (Dipt.: Tachinidae)
The oleander scale, Aspidiotus nerii Bouche and the palm scale, Hemiberlesia lataniae (Sign.) (Hem.: Diaspididae) occur sporadically on macadamia. The oleander scale may be found on the leaves and branches and the palm scale on the husks.
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