In the last decades, agriculture has passed through an intensification process by drastically increasing the land devoted to farming for food production (Foley et al. 2005). This process has resulted in the loss of natural habitats which in turn has provoked a loss of biodiversity and a reduction of the ecosystem services associated with it (Dirzo et al. 2014). In addition, this landscape simplification process increases the likelihood of more damaging and catastrophic pest outbreaks (Paredes et al. 2021), which has intensified farmers' dependence on insecticides. However, the resistance of pests to insecticides is augmenting, even exceeding the capacity to generate new products to combat these pests (Gould et al. 2018). Because of this, new policies are promoting the use of sustainable solutions for pest management that do not imply the use of this kind of products (European Comission 2020). Despite most of the techniques that have been tested are orientated towards its implementation at the local level, ecologists, agronomists and farmers are increasingly recognizing the critical role that surrounding landscapes can play in determining pest damage (Thies and Tscharntke 1999; Bianchi et al. 2006).
Simplified landscapes (i.e., expansive monocultures) can increase pest outbreaks because they promote specialized pest populations to develop and spread more easily, whereas complex landscapes (i.e., mosaics of different land uses) can be a barrier that hamper this expansion (Root 1973; O’Rourke and Petersen 2017). On the other hand, diversified landscapes can promote pest natural enemies (predators and parasitoids) by providing resources such as shelter, nectar, pollen and/or alternative prey for their optimal development, thus improving their action against pests (Landis et al. 2000; Chaplin-Kramer et al. 2011). Therefore, planting multiple crops or retaining non-crop vegetation may lower pest densities and reduce insecticide applications (Dainese et al. 2019; Paredes et al. 2021). However, pests can also use other land uses in the landscape for their development thus increasing their presence into the crop (Tscharntke et al. 2016). For example, in Africa, corn stemborers appeared to be promoted by grasslands (Midega et al. 2014), which aligns with another study in Australia that also showed natural grasslands as a source of pest (Parry et al. 2015). Perhaps, the most critical case is the invasive pest species Drosophila suzukii that seems to be positively affected by natural habitats at the landscape scale, by using alternative hosts to thrive (Santoiemma et al. 2018) and also because these habitats provide better protection against adverse weather conditions during winter and summer periods (Santoiemma et al. 2019). Thus, the inconsistency of pest responses to landscape complexity prevents researchers to emit clear conclusions about the role of landscape on pest control (Karp et al. 2018). It also highlighting the importance of pest species’ traits to elucidate its responses to landscape composition (Tamburini et al. 2020) as well as on how they interact with the different elements in the landscape.
Bactrocera oleae (Rossi) is the major olive pest that induces economic losses worldwide totaling approximately 15% per year (Montiel-Bueno and Jones 2001). The effect of landscape context on this pest is not well defined. For example, a study performed in southern Spain showed a reduction of this pest in areas with more natural habitat edge density, landscape diversity and higher number of patches of natural vegetation (Ortega and Pascual 2014). However, another study carried out in Italy did not find any effect of natural habitats on B. oleae abundance (Picchi et al. 2016), whereas another work developed in southern Spain showed a positive effect of natural habitats on B. oleae abundance (Manjón-Cabeza et al. 2017). The stochasticity that pest populations have may be behind these contrasting results (Chaplin-Kramer et al. 2013; Paredes et al. 2021). However, neither of these studies nor most of the others regarding the effect of landscape on other pests (but see Santoiemma et al. 2019) have ever explored whether the population dynamics of this pest in other land uses is different or similar from that in the olive grove.
Even more, the olive fly has a period during the year in which it disappears from the olive groves. This is called the “white period” that takes place in the months of May and June when the abundance of olive fly in the field suddenly drops and there are no olive fruits to attack (Michelakis and Neuenschwander 1981). During this period, the olive fly can move in the landscape looking for other resources that ultimately can reinforce its population when this start rising in Autumn (Marchini et al. 2017). Therefore, to understand the population dynamics of B. oleae in other land uses is critical to understand the importance of a landscape perspective in the management of this pest and how can we better promote natural pest control mechanisms based on landscape management (Daane and Johnson 2010).
Here we purpose a study in which we investigate the dynamics of B. oleae in the different land uses that compound a typical olive landscape in Portugal. We aim at answering the following questions: (1) To what extent is Bactrocera oleae present in the different land uses, including olive grove? (2) Which are the dynamics of B. oleae in these land uses? and, (3) How different land uses at the landscape scale affect the abundance of Bactrocera oleae in olive groves?