Methiocarb-Induced Aversion to Grapes by Gray-Backed White-Eyes

Abstract

Gray-backed white-eyes (Zosterops lateralis) formed a conditioned aversion to grapes sprayed with methiocarb but not when a visual mimic, calcium phosphate, was substituted. The birds did not use a visual cue to distinguish between treated and untreated grapes, but probably used a taste cue. White-eyes that had previously eaten grapes formed a specific aversion while those that had not eaten grapes formed a nonspecific aversion. This suggests methiocarb can be successfully used as a border treatment for protection of crops from 1st-year birds. If invading birds are older and therefore at eating grapes, the entire crop would need to be treated. J. WILDL. MANAGE. 48(2):444-449 Damage to grapes by the gray-backed white-eye was a problem of economic proportions in Western Australia during the early development of the colony (Hallack 1891, Anonymous 1904, Milligan 1904). Despite the continuing loss of production and the lowering of wine quality caused by this bird, there has been little scientific effort devoted toward alleviating the problem. Apart from the limited use of a promising acoustic device that interferes with the birds' communication system (Knight and Robinson 1978a,b), methods of control have advanced little beyond shooting the birds and picking the crop early. Investigations were initiated in southwest Western Australia, near Margaret River (34?00'S, 115000'E), to ascertain the efficacy of the insecticide, molluscicide, and avian emetic, methiocarb [4-(methylthio)-3,5-xylyl N-methyl carbamate] in protecting ripening grapes from whiteeyes. Methiocarb repels birds from crops (Guarino 1972, Stone et al. 1974, Porter 1977, Henkes 1979, Ruelle and Bruggers 1979). It can also protect grapes from depredations by white-eyes (Bailey and Smith 1979, Menzies 1979). A recent study has shown, however, that methiocarb reduces crop depredations by birds because, in some instances, it reduces insect numbers; thus the birds find a crop with few insects an unacceptable area in which to forage (Woronecki et al. 1981). Some evidence is available which suggests that the reported crop protection provided by methiocarb has a more direct, physiological-psychological basis. Rogers (1974) demonstrated that methiocarb causes a response to feeding in redwinged blackbirds (Agelaius phoeniceus) similar to that caused by lithium chloride, an agent well known for forming conditioned aversions. Rogers (1978) also found that redwings form a specific conditioned aversion to two foods, a formulated product and finely ground rice, treated with methiocarb and that the cue used in the formation of the aversion is probably taste. Rooke (1983) demonstrated that whiteeyes develop a specific conditioned aversion to their food when it has methiocarb added if a visual cue is provided. In the absence of a visual cue, food consumption decreased due to a nonspecific aversion or to debilitation caused by methiocarb. Thus, methiocarb has the potential to directly deter white-eyes from eating grapes rather than merely reducing damage in a vineyard by making the area unaccept444 J. Wildl. Manage. 48(2):1984 This content downloaded from 157.55.39.177 on Tue, 15 Nov 2016 04:02:18 UTC All use subject to http://about.jstor.org/terms METHIOCARB-INDUCED AVERSION IN WHITE-EYES * Rooke 445 able for foraging because of methiocarb's insecticidal properties. The present study was conducted to determine whether white-eyes develop a conditioned aversion to grapes sprayed with methiocarb (experiment I). If the cue used by white-eyes in the formation of a specific aversion to treated grapes is visual, then it should be possible to use a visual mimic of methiocarb to form an aversion in birds that have previously eaten grapes treated with methiocarb. Such a mimic could be cheaper and nontoxic and, therefore, more compatible with the grape and wine industries. To test this possibility, a second experiment was conducted to determine whether calcium phosphate would act as a visual mimic of methiocarb in the formation of an aversion (experiment II). The two experiments were conducted using white-eyes whose previous experience with eating grapes was unknown. In a vineyard there would be two classes of birds: adults that had eaten grapes in previous seasons, and 1st-year birds that had not had the opportunity to eat grapes. Because it is well known that animals readily form aversions to novel food but not to familiar food (Revusky and Bedarf 1967, Wittlin and Brookshire 1968, Shettleworth 1972), it is likely that experienced grape-eaters would not as readily form an aversion to treated grapes as animals to which grapes were novel. To test this hypothesis, experiments were conducted to determine the difference in aversive behavior between these two classes of white-eyes (experiments III, IV).