The economic value of natural regulation of agricultural pests by bats has been estimated both by avoided cost models and by experimental predator-exclusion approaches. We review published studies globally from both complementary approaches. We further present an economic model for the avoided cost of bat predation on stinkbugs, the major economic pest of macadamias in South Africa, currently the world's largest macadamia producer. We calculated both the direct (reduced stinkbug damage due to bat predation) and indirect (reduced pesticide use) avoided costs. We estimated the density of bats in a macadamia-growing region of South Africa to be 7.5-22.5 bats/ha, based on opportunistic data from the Merlin DeTEct (Inc.) avian-avoidance radar system. Current economic parameters for macadamia production, stinkbug injury coefficients and life history were obtained from the literature and from the Southern African Macadamia Association (SAMAC).We estimated the level of bat predation on pest stinkbugs in macadamia orchards from published dietary studies combined with both high and low published values for insect consumption rates relative to bat body mass. We found that the protected yield due to bat predation of stink bugs amounted to 0.53% (low consumption rates) to 1.29% (high consumption rates) of annual macadamia production in South Africa for 2015. Based on current macadamia prices, the approximate avoided cost values of these combined direct and indirect bat predation services varied between 9% and 23% of the current annual estimated cost of damage caused by stinkbugs to South African macadamia orchards (US$613/ha). Losing bats to disease epidemics, wind farms, human persecution or excessive or highly toxic pesticide applications could therefore significantly increase annual losses to the macadamia industry in South Africa caused by stinkbugs.

1. The relative importance of ecosystem services and disservices can change with landscape structure in a poorly understood way.2. We compare the impact of biocontrol, provided by bats and birds, with that of crop raiding by vervet monkeys on yield in South African macadamia orchards.Insectivorous bats and birds are known to feed on macadamia pest insect species, like the macadamia nut borer or the green vegetable bug. Vervet monkeys move into the orchards during the day to feed on premature macadamia nuts. Bats, birds and monkeys benefit from patches of natural vegetation adjacent to orchards. With exclusion experiments (four treatments: day, night, day and night, control) we quantified the relative importance of biocontrol and crop raiding on yield, comparing two different landscape settings of the orchards, a natural and a human-modified. 4. Crop raiding occurred only close to natural vegetation and caused yield losses of about 26%. Biocontrol by bats and birds was higher near natural vegetation, but still significant in human-modified landscapes, at up to 530 m distance to forest patches. Prevented biocontrol through the exclusion of bats and birds resulted in yield losses of up to 60%.5. Effects of biocontrol by bats and birds (USD ~5,000 ha/year) were economically more important than the losses of crop raiding (USD ~1,600 ha/year). As both are linked to the vicinity of forest patches, the removal of natural vegetation to limit monkey abundances would also limit biocontrol service provision. Synthesis and applications.This study highlights the high economic benefits of biocontrol by bats and birds, which outweighed negative impacts through yield losses caused by crop raiding monkeys. Management practices to prevent crop damage, such as guarding, excluding vertebrates or removal of adjacent natural vegetation, would also limit access for bats and birds and the great economic benefits provided by their biocontrol. Ecosystem services by bats and birds can be promoted by the exposure of artificial roost and nest sites, but research into species-specific preferences is needed. The education of farmers is crucial, as many are unaware 2070 | Journal of Applied Ecology LINDEN Et aL.

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Abstract:Fruit fly species' responses to lures are critically important, especially when a single lure might be recommended for the purpose of trapping multiple fruit fly species in commercial fruit orchards. Fruit industries are facing threats from the recent invasion of the oriental fruit fly Bactrocera dorsalis (Hendel) into novel areas in South Africa. The objective of this study was to test the relative efficiency of 13 different trapping systems for fruit fly species in mango orchards in South Africa. Evaluation of the different monitoring systems was conducted during the 2013-2014 mango season in the Vhembe district municipality of Limpopo, South Africa. Four orchards, where Tommy Atkins was cultivated, were used to compare the efficacy of the trapping systems. Trapping data (N = 48 observation incidences per trapping system) were analyzed using a non-parametric ANOVA. Pronounced variation in species attractiveness across the trapping systems was found. The enriched ginger oil (EGO) Pherolure TM captured 33.77% of all the Ceratitis spp., while the Invader-lure TM captured 36.47% of the total number of B. dorsalis trapped. Torula yeast pellets are not recommended for fruit fly trapping due to the relative low trap catch numbers and high non-target catches. These results are important and significant for on-farm monitoring strategies, as well as for invasion monitoring systems currently in place to detect the distribution of B. dorsalis in South Africa.

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