Many farmers have reacted by applying ever more pesticide, which has only served to exacerbate the problem as natural predators to harmful insects are also eliminated, detrimentally affecting the entire ecology within orchards.
One of South Africa’s largest macadamia production areas, Levubu in Limpopo, happens to be home to 14 bat species. This, coupled with the economic significance that bats could offer macadamia farmers, led Dr Valerie Linden, from the Centre for Invasion Biology at the University of Venda, to conduct research that could eventually see bats protected and nurtured by the agricultural community.
“众所周知，蝙蝠在南非麦卡露达果园活跃，并归因于主要的昆虫害虫物种，如绿色蔬菜虫（内扎拉泼妇），澳洲坚果博勒（Cryptophlebia Ombrodelta），双察觉臭虫（Bathycoelia Natalicola）和荔枝蛾（C.Peltastica），“林登说。
“What we didn’t know was just how much of the pest insect population these bats consumed, which is what we set out to study.
“In Levubu, many other crops or even areas of natural bush are being removed and replaced with macadamias. The crop is highly valuable, so it’s an ideal species to study if you want to look at the economic impacts of the presence or absence of biocontrol agents such as bats. Macadamias are under high insect pressure, which was another criterion.
“We ultimately found that farmers could save as much as R76 300/ ha in reduced nut damage as a result of bats keeping stink bugs under control.”
“Many people are unaware of the benefits provided by bats as well as their general presence, so they’re hardly missed, and declines in their numbers aren’t noticed directly.”
For the study, Linden created a scenario where bats and birds were absent from macadamia trees.
Cages were constructed around macadamia trees enclosed with nylon mesh net that would keep larger animals out, but would let insects through to gain access to the trees.
Linden also found that the impact of bats as natural pest control in macadamias was higher in trees close to natural habitat than in trees away from any natural vegetation. Benefits could be seen up to 530m from the natural vegetation.
“虽然这些天然植被的斑块也可以产生问题，因为它们是猴子等作物攻略的栖息地，但我的结果表明，远离这些补丁的益处远远超过了缺点。通过蝙蝠和这些自然边缘附近的蝙蝠和鸟类的更高生物控制节省，这些天然边缘在学习区域上涨至R76 500，远远高于通过猴子袭击的测量损失，即R24 500。“
蝙蝠和鸟类的排斥了60% decrease in yield compared with the control. The exclusion of both bats and birds therefore resulted in an income loss of around R76 300/ ha. The reduced income losses for the exclusion of diurnal birds totalled around R60 200/ ha, and for bats and nocturnal birds about R37 000/ha.
为了进一步突出了蝙蝠的能力s to assist with pest control, Linden recorded bat numbers throughout the year and found that an increase in bats correlated with the macadamia nut season.
creating a bat-friendly environment
While bats have proved their worth in macadamia orchards, keeping their numbers sufficiently high is a challenge. An ever-growing human population and related land use changes, especially agricultural intensification, have led to a threat of extinction of about one quarter of bat species globally.
“The importance of landscape features and connectivity within an agricultural landscape for bats has been proved. It’s therefore recommended that farmers increase or at least maintain the amount of natural vegetation around agricultural areas, considering the significantly higher pest control services. Other ecosystem services, such as pollination, could also be enhanced by natural vegetation and be compromised by its removal or isolation.”
Linden believes education is an important tool in protecting natural areas around agricultural land, highlighting the valuable benefits, which can outweigh its costs.
The proactive management of bat populations is indispensable to sustaining the ecosystem services they provide. This means that farmers need to follow a combination of practices, which include decreasing pesticide use, leaving natural habitats intact and erecting bat houses.
Linden cautions that while Levubu farmers are fortunate in that the bat diversity is particularly high in this area, she found evidence that clutter-feeding bat species, which are generally more sensitive to disturbances and pesticide application, are more or less absent from the orchards.
“So although bats are around the orchards, farmers need to be aware how management practices can affect natural predators.
“To further promote bird and bat populations and thereby potentially increase the value of biological control, artificial nesting and roosting sites can be provided to encourage bats to inhabit agricultural areas, where natural habitat is scarce. This can be more cost-efficient than pesticide treatments in keeping pest species under a certain threshold.”
Unfortunately, artificial roosts, such as bat houses, cannot entirely replace natural roosts, as they are suitable only for some species. Linden has found, however, that bat houses are a good way to establish large colonies of certain bats around orchards.
“The most important aspect is durability. It can take up to five years for bats to occupy a house, so ideally your bat house must be able to last longer than that.”
She notes that while bats are not a complete solution to pest insect problems in orchards, and like any other predator cannot completely eliminate pests, they can control them effectively.
“If you can establish a healthy bat population on your farm, pest numbers and, with that, the need for pesticide, will go down. This, in turn, might increase bat activity in the orchards and pest numbers will decrease further.”
Email Dr Valerie Linden at[email protected]。