Habitat loss is often considered the greatest near-term threat to biodiversity. Yet the impact of habitat fragmentation, or the change in habitat configuration for a given amount of habitat loss, has been intensely debated. We isolated effects of habitat loss from fragmentation on the demography, movement, and abundance of wild populations of a specialist herbivore, Chelinidea vittiger, by removing 2,088 patches across 15 landscapes. We compared fragmentation resulting from random loss, which is often considered in theory, to aggregated loss, which is often observed in the real world. When quantifying fragmentation caused by random vs. aggregated loss, aggregated loss led to less fragmented landscapes than random loss based on patch isolation, but more fragmented landscapes when based on isolation at a larger mesoscale scale defined by dispersal distances of C. vittiger. Overall, habitat loss decreased population size and demographic parameters, with thresholds occurring at approximately 70-80% patch loss. Synergistic effects also occurred, where an aggregated pattern of loss had negative effects at low, but not high, amounts of habitat loss. Effects on population size of C. vittiger were driven by reductions in movement and subsequent reproduction. The direction of habitat fragmentation effects from random and aggregated loss treatments, for a given habitat amount, was conflictingly positive or negative depending on the scale at which fragmentation was quantified. Fragmentation quantified at the scale of dispersal for this species best explained population size and highlighted that fragmentation had negative effects at a mesoscale. Our results emphasize the importance of quantifying habitat fragmentation at biologically appropriate scales.

To combat climate change, farmers must innovate through ecological intensification to boost food production, increase resilience to weather extremes, and shrink the carbon footprint of agriculture. Intercropping (where alternative crops or noncrop plants are integrated with cash crops) can strengthen and stabilize agroecosystems under climate change by improving resource use efficiency, enhancing soil water holding capacity, and increasing the diversity and quality of habitat for beneficial insects that provide pollination services and natural pest control. Despite these benefits, intercropping has yet to be widely adopted due to perceived risks and challenges including decreased crop yield, increased management complexity, a steep learning curve for successful management, and increased susceptibility to pests. Here, we explore the major benefits of intercropping in agricultural systems for pest control and climate resilience reported in 24 meta-analyses, while addressing risks and barriers to implementation. Most studies demonstrate clear benefits of intercropping for weed, pathogen, insect pest control, relative yield, and gross profitability. However, relatively few studies document ecosystem services conferred by intercrops alongside labor costs, which are key to economic sustainability for farmers. In addition to clearer demonstrations of the economic viability of intercropping, farmers also need strong technical and financial support during the adoption process to help them troubleshoot the site-specific complexities and challenges of managing polycultures. Ecological intensification of agriculture requires a more strategic approach than simplified production systems and is not without risks and challenges. Calibrating incentive programs to reduce financial burdens of risk for farmers could promote more widespread adoption of intercropping.

In many organisms, phenotype and fitness are strongly influenced by both current environmental factors and maternal effects. The low genetic variation, high phenotypic plasticity, and telescoping generations seen in aphids permit us to investigate the relative importance and potential interaction of maternal and current environments on phenotype. Although past studies have identified an influence of maternal host plant on offspring phenotype and reproduction in aphids, few have demonstrated the potential for these maternal effects to also interact with the aphid's current environment. By rearing multiple generations of Aphis nerii (Fonscolombe) (Hemiptera: Aphididae) on their host common milkweed, Asclepias syriaca (L.) (Apocynaceae), we tested the relative influence and interaction of both maternal and current environmental effects of crowding and plant quality on aphid body size and reproduction. Our results indicate that aphid body size increased with current plant quality and decreased with aphid density in both generations, with an additional direct, positive relationship between body size and fecundity. We did not find evidence for adaptive maternal effects, e.g., production of fewer, larger, offspring by stressed mothers. Instead, poor maternal environments constrained aphid body size and reproduction. Importantly, these adverse maternal effects were only seen in offspring where subsequent nymph population growth was allowed to increase unchecked, likely reducing available resources. Our study thus demonstrates that the significance of maternal effects in aphid development and reproduction can depend on current resource availability, shaping the phenotype and fecundity of offspring under stressful conditions. Incorporating this framework for how aphid body size and reproduction respond to current and maternal environments may improve predictions for how aphid population growth is impacted by resource limitation across generations.

At small spatial scales, attraction or deterrence of herbivores by plant neighbors can alter the susceptibility of plants to damage (i.e., associational effects). Given the patchy nature of plants and insect herbivory, we hypothesized that induced resistance may play an important role in mitigating such spatial variability. To test this notion, we first documented neighbor effects between two closely related and co-occurring plant species in natural populations, and second, we measured how these effects changed after inducing plant resistance in a common garden. In wet fields and marshes of Northeastern North America, boneset (Eupatorium perfoliatum) is the primary host for the herbivorous beetle Ophraella notata. Across two years of surveys at multiple sites, we found that Joe Pye weed (Eutrochium maculatum) was a secondary host to O. notata and was more likely to receive beetle eggs when it grew near boneset, constituting a negative neighbor effect (associational susceptibility) for Joe Pye weed. Reciprocally, there were trends of reduced susceptibility for boneset when it grew near Joe Pye weed (a positive neighbor effect), but this pattern was less consistent over space and time. In the common garden, we manipulated patches, each with a center (focal) and surrounding (neighbor) plants, with focal plants of each species either induced by the plant hormone jasmonic acid or left as controls. While neighbor effects prior to induction mirrored the pattern in surveys, induction was most effective in reducing beetle oviposition on focal plants in heterospecific groups. This effectively eliminated negative neighbor effects (susceptibility) for Joe Pye weed, the less preferred plant species. However, in conspecific patches, induction had minimal effect on either species' susceptibility to beetles. Given the importance of spatial variation generally and the ubiquity of neighbor effects in plant communities, we suggest that inducible resistance may be an important mechanism to cope with spatial heterogeneity in susceptibility to herbivores.

No abstract