While ant activity only significantly increased after string placement on connected coffee plants, we also observed lesser increases in ant activity on control coffee plants and nest trees . This unexpected result could mean that strings, a novel element in the environment, acted as a form of habitat modification or disturbance, which increased overall ant activity in the local area. However, if our manipulation was the cause, we would have expected the ants to attack the jute strings , a behavior that we did not observe during the experiment. Experiments in tropical forests have shown that the long-term removal of lianas can influence ant richness on trees , and therefore may possibly also affect overall ant abundance and activity when promoted. It is also possible that other factors could potentially explain this result in control plants, such as changes in local abiotic factors that we did not measure systematically in our experiment. Future research which expands on the temporal scope of this study may be useful in assessing the long-term effects of artificial connectivity in this system. Ant activity after string placement was negatively affected by distance to the nesting tree . This result is consistent with previous studies suggesting that within 5 m A. sericeasur dominance in the leaf litter decreases with distance to the nesting tree . However, in our study, grow bag the effect of distance after string placement was significant only on control plants, but not on connected plants. This suggests that connections could buffer the negative effects that larger distances from the nesting tree pose to ant activity and potentially increase antprovided biological control services in these plants. Connected coffee plants also had significantly higher CBB removal than control plants .

Overall, greater ant activity on coffee plants was associated with higher CBB removal rates , suggesting that ant activity directly influenced CBB removal rates. However, while this effect was significant on control coffee plants, it was only marginally significant on connected plants. While we believe that these results support the hypothesis that connectivity enhances ant foraging and bio-control services on coffee, the use of dead CBB in this experiment as a proxy to measure bio-control may explain the only marginally significant effect of ant activity on CBB removal in connected plants. It is possible that dead prey exhibit more variable recruitment responses from ants than live prey. Despite this, it is likely that strings facilitated ant movement to coffee plants by providing a smooth, linear substrate and indirectly increased CBB removal . In other systems, the leaf-cutting ant Atta cephalotes uses fallen branches to rapidly move between areas and thereby quickly discover new food resources . Similarly, these resources allow scouts to return quickly to the colony, minimizing the time taken for information transfer and recruitment of other foraging workers . The role of trunk trails and fallen branches has received extensive attention in the leaf-cutting ant system; however, fewer studies have looked at the influence of connectivity resources on foraging behavior of predatory arboreal ants. Surprisingly, CBB removal did not follow the same trend as ant activity with distance to the nesting tree. While control plants tended to have lower CBB removal rates than connected plants as distance to the tree increased, we did not find a significant effect of distance on CBB removal in either control or connected plant groups. Collectively, these results suggest that connections in the arboreal stratum have the potential to increase ant activity and therefore enhance plant protection from CBB attack, particularly in connected plants.

Further studies should assess the effect of distance on CBB removal using plants located at distances larger than 3.5 m from the tree. It is important to note that enhanced ant activity on coffee plants could lead to increases in the density of ant-tended hemipterans, such as the green coffee scale, which if severe enough could reduce the productivity of coffee plants. However, the green coffee scale is not a major pest in the region of study, in contrast to the economically significant coffee berry borer . Furthermore, a recent study evaluating the benefits associated with the indirect Azteca–Coffea mutualism found that the protective benefit ants provide to coffee plants is positively associated with high densities of the scale . This suggests that the enhanced CBB control by ants outweighs the costs associated with scale damage. However, these interactions may be context-dependent and still need to be fully evaluated in the field to provide a holistic understanding of the impact of connectivity on scale density and coffee yield. Other ant species could also benefit from the addition of connections between coffee plants and shade trees, such as C. basalis and P. simplex, which were observed using these connections during our study. The ant P. simplex has been previously reported as an important CBB bio-control agent, acting in conjunction with other species of ants to effectively suppress CBB at various life stages . Therefore, this technique could support Azteca ants as well as other ant species that play an important role in suppressing CBB populations. Our results support the general hypothesis that connectivity, one measure of habitat complexity, can sustain important ecological processes in natural and managed ecosystems. In aquatic systems, more complex habitats with macrophytes allow for greater food capture and maintain higher levels of diversity . In terrestrial systems, higher complexity can influence trophic dynamics . In coffee agroecosystems, ants are highly sensitive to habitat change and management intensification, generally expressed as the reduction of shade, elimination of epiphytes, and use of chemical inputs . Such intensification can have a negative effect not only on vegetation connectivity and ant foraging, but may also cascade to affect ecosystem services, such as biological control.

Our study supports the idea that promoting complexity at a local scale, in this case providing structural resources for ants in agroecosystems, can significantly enhance connectivity within the arboreal strata, and potentially improve biological control of coffee pests. This idea has already been successfully implemented in other agricultural systems, placing “ant bridges” made of bamboo strips or strings connecting neighboring trees in , and could be incorporated as a management strategy in coffee systems. Future research should evaluate the practical feasibility of adding connections between vegetation strata to enhance bio-control. For example, studies in timber plantations have estimated that the presence of ants increases timber production by 40%, and that ants can be maintained at lower costs by providing intra-colony host tree connections using rope, poles or lianas . It is important that future studies in coffee also consider the costs of other CBB control methods, such as the application of the pesticide endosulfan, which can lead to the development of resistance, can negatively impact natural enemies, and can have harmful impacts on human health . Further investigation into promoting ant bio-control with artificial connections in coffee should: assess economic trade-offs, management applicability, and farmers’ perceptions of this method in large and small coffee plantations, compare the cost between string placement and other management approaches , grow bag gardening and assess coffee yields on connected and not connected plants to provide management recommendations. More broadly, incorporating conservation bio-control strategies in combination with vegetation connectivity is consistent with criteria identified as key for the sustainability of biological control, such as increasing local habitat quality and enhancing species’ dispersal ability . Generally, the maintenance of shade trees and natural vegetation in agroforestry systems may increase vegetation complexity and natural connectivity between plants to promote ant foraging and subsequent biological pest control.The HPA axis maintains a diurnal rhythm marked by a daily peak after waking, a subsequent decline over the course of the day, and a nadir shortly after onset of continuous sleep . The diurnal pattern of HPA activity plays important roles in a variety of metabolic, immunological, and psychological processes that support our day-to-day functioning . In studies of children, the preferred assessment method of HPA axis activity is the collection of saliva and the measurement of cortisol . Cortisol is the “end-product” hormone released into the bloodstream from the adrenal glands—the final step in a biological cascade initiated by the hypothalamus and perpetuated by the pituitary gland. In addition to supporting the orchestration of several other processes , moderate cortisol levels are thought to support effective neural transmission and optimal learning and high-order cognition . In times of acute physiological or psychological stress, the HPA axis mounts a particularly pronounced response, culminating in high levels of cortisol that reach glucocorticoid receptors throughout the body and brain. Working with the ANS, these acute HPA stress responses coordinate the physiological and psychological resources needed to overcome the stressor . Yet, given negative feedback processes, high cortisol levels also play important regulatory roles in down-regulating HPA axis activation, allowing it and other systems to return to baseline . Collectively, these complex within- and cross-system dynamics support an organism’s ability to both respond to and recover from the effects of environmental stressors . HPA axis reactivity and regulation are evident very early in life. Newborn infants can mount an HPA axis response to environmental stimuli , and normative circadian rhythms tend to stabilize as infants begin to forego their afternoon naps .

However, the span from infancy through early childhood is also a time of meaningful developmental change. Indeed, a growing theoretical and empirical literature indicates that children’s early experiences play a critical role in the organization of their emerging adrenocortical systems .Low-income ecologies present a confluence of distal and proximal risk factors thought to influence children’s developing physiological stress systems and undermine optimal cognitive and social development . For example, children growing up in low-income contexts are more likely to face distal stressors, such as inhospitable and dangerous neighborhoods and inadequate access to services and social capital . Such distal risks are known to have trickle-down effects that undermine parents’ abilities to effectively read, interpret, and respond to their children’s needs . In turn, a convergent literature comprising experimental work with animals as well as observational studies of young children indicates that sensitive and responsive caregiving can support adaptive HPA axis functioning . This is evident with respect to children’s acute stress responses. For example, young children with secure attachment relationships and more sensitive caregivers tend to show better regulated HPA axis responses when faced with acute psychological stressors . Changes in the quality of children’s caregiving environments have also been linked with their baseline, or resting levels of HPA axis activity. For example, at the more extreme end, children who are moved from very high-risk households into foster care have been found to evince comparatively lower resting cortisol levels than their peers who remain in high-risk homes . For instance, in prior work with the same sample as used in the present study, our group showed that higher levels of maternal sensitivity in infancy are predictive lower levels of resting cortisol, after adjusting for income and a number of potential confounds . Beyond psychosocial risks, children growing in the context of economic adversity are more apt be exposed to households that are more densely populated, noisy, disorganized, and unpredictable—aspects typically discussed under the umbrella term chaos . A growing literature suggests that chaotic environments may alter children’s ANS and HPA axis functioning in early and middle childhood. Recent work by researchers in our laboratory suggests similar effects with respect to infants and toddlers , with within-child increases in chaos predictive of contemporaneous increases in resting salivary cortisol in later infancy and toddlerhood.Notably, young children growing up in low-income contexts spend substantial amounts of time in settings outside of their homes—such as non-parental child care. Indeed, in the United States approximately 43% of children in poverty attend regular non-parental care by 9 months of age . A well-developed literature indicates that young children’s early child care experiences also play a meaningful role in their HPA axis functioning. Meta-analytic findings indicate that—compared to their normal diurnal patterns experienced at home—children tend to show cortisol increases across the day on days when they attend child care . Some work suggests these patterns are particularly strong in toddlerhood and the beginning of the early childhood years and for children who attend lower quality child care . There is also some, albeit limited, evidence of long-term effects; for example, Roisman and colleagues found that spending greater proportions of time in center-based care in infancy and early childhood was predictive of children’s subsequent cortisol awakening response in adolescence.