Species range expansion induced by climate change and human activities threaten native populations and communities across the biosphere. Insect herbivores, important consumers of plants, are known to expand or contract their range under global change, with potential consequences to the newly reached environment. The selection of oviposition sites by herbivorous insects could notably impact offspring performance. However, the role of such effects in impacting the receiving ecosystem has been rarely explored. Here, we provide the first evidence showing that a terrestrial range‐expanding phytophagous wood‐borer moth (
- NSF-PAR ID:
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Land Degradation & Development
- Page Range / eLocation ID:
- p. 3023-3035
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Background Oviposition decisions are critical to the fitness of herbivorous insects and are often impacted by the availability and condition of host plants. Monarch butterflies ( Danaus plexippus ) rely on milkweeds ( Asclepias spp.) for egg-laying and as food for larvae. Previous work has shown that monarchs prefer to oviposit on recently regrown plant tissues (after removal of above-ground biomass) while larvae grow poorly on plants previously damaged by insects. We hypothesized that these effects may depend on the life-history strategy of plants, as clonal and non-clonal milkweed species differ in resource allocation and defense strategies. Methodology/Principal Findings We first confirmed butterfly preference for regrown tissue in a field survey of paired mowed and unmowed plots of the common milkweed A. syriaca . We then experimentally studied the effects of plant damage (comparing undamaged controls to plants clipped and regrown, or damaged by insects) on oviposition choice, larval performance, and leaf quality of two closely related clonal and non-clonal species pairs: (1) A. syriaca and A. tuberosa , and (2) A. verticillata and A. incarnata . Clonal and non-clonal species displayed different responses to plant damage, impacting the proportions of eggs laid on plants. Clonal species had similar mean proportions of eggs on regrown and control plants (≈35–40% each), but fewer on insect-damaged plants (≈20%). Meanwhile non-clonal species had similar oviposition on insect-damaged and control plants (20–30% each) but more eggs on regrown plants (40–60%). Trait analyses showed reduced defenses in regrown plants and we found some evidence, although variable, for negative effects of insect damage on subsequent larval performance. Conclusions/Significance Overall, non-clonal species are more susceptible and preferred by monarch butterflies following clipping, while clonal species show tolerance to clipping and induced defense to insect herbivory. These results have implications for monarch conservation strategies that involve milkweed habitat management by mowing. More generally, plant life-history may mediate growth and defense strategies, explaining species-level variation in responses to different types of damage.more » « less
Mansour, Ramzi (Ed.)The preference-performance hypothesis explains host specificity in phytophagous insects, positing that host plants chosen by adults confer the greatest larval fitness. However, adults sometimes oviposit on plants supporting low larval success because the components of host specificity (adult preference, plant palatability, and larval survival) are non-binary and not necessarily correlated. Palatability (willingness to eat) is governed by chemical cues and physical barriers such as trichomes, while survival (ability to complete development) depends upon nutrition and toxicity. Absence of a correlation between the components of host specificity results in low-performance hosts supporting limited larval development. Most studies of specificity focus on oviposition behavior leaving the importance and basis of palatability and survival under-explored. We conducted a comprehensive review of 127 plant species that have been claimed or tested to be hosts for the monarch butterfly Danaus plexippus to classify them as non-hosts, low performance, or high performance. We performed a meta-analysis to test if performance status could be explained by properties of neurotoxic cardenolides or trichome density. We also conducted a no-choice larval feeding experiment to identify causes of low performance. We identified 34 high performance, 42 low performance, 33 non-hosts, and 18 species with unsubstantiated claims. Mean cardenolide concentration was greater in high- than low-performance hosts and a significant predictor of host status, suggesting possible evolutionary trade-offs in monarch specialization. Other cardenolide properties and trichome density were not significant predictors of host status. In the experiment, we found, of the 62% of larvae that attempted to eat low-performance hosts, only 3.5% survived to adult compared to 85% of those on the high-performance host, demonstrating that multiple factors affect larval host plant specificity. Our study is the first to classify all known host plants for monarchs and has conservation implications for this threatened species.more » « less
Intensifying drought conditions across the western United States due to global climate change are altering plant–insect interactions. Specialist herbivores must find their host plants within a matrix of nonhosts, and thus often rely upon specific plant secondary chemistry for host location and oviposition cues. Climate-induced alterations to plant chemistry could thus affect female selection of larval food plants. Here, we investigated whether host-plant water limitation influenced oviposition preference in a threatened invertebrate: the monarch butterfly (Danaus plexippus). We found that females deposited more eggs on reduced-water than on well-watered narrowleaf milkweed plants (Asclepias fascicularis), but we could not attribute this change to any specific change in plant chemistry. Specialist herbivores, such as the monarch butterfly, which are tightly linked to specific plant cues, may experience shift in preferences under global-change conditions. Understanding oviposition preferences will be important to directing ongoing habitat restoration activities for this declining insect.
A key to understanding life's great diversity is discerning how competing organisms divide limiting resources to coexist in diverse communities. While temporal resource partitioning has long been hypothesized to reduce the negative effects of interspecific competition, empirical evidence suggests that time may not often be an axis along which animal species routinely subdivide resources. Here, we present evidence to the contrary in the world's most biodiverse group of animals: insect parasites (parasitoids). Specifically, we conducted a meta‐analysis of 64 studies from 41 publications to determine if temporal resource partitioning
viavariation in the timing of a key life‐history trait, egg deposition (oviposition), mitigates interspecific competition between species pairs sharing the same insect host. When competing species were manipulated to oviposit at (or near) the same time in or on a single host in the laboratory, competition was common, and one species was typically inherently superior (i.e. survived to adulthood a greater proportion of the time). In most cases, however, the inferior competitor could gain a survivorship advantage by ovipositing earlier (or in a smaller number of cases later) into shared hosts. Moreover, this positive (or in a few cases negative) priority advantage gained by the inferior competitor increased as the interval between oviposition times became greater. The results from manipulative experiments were also correlated with patterns of life‐history timing and demography in nature: the more inherently competitively inferior a species was in the laboratory, the greater the interval between oviposition times of taxa in co‐occurring populations. Additionally, the larger the interval between oviposition times of competing taxa, the more abundant the inferior species was in populations where competitors were known to coexist. Overall, our findings suggest that temporal resource partitioning viavariation in oviposition timing may help to facilitate species coexistence and structures diverse insect communities by altering demographic measures of species success. We argue that the lack of evidence for a more prominent role of temporal resource partitioning in promoting species coexistence may reflect taxonomic differences, with a bias towards larger‐sized animals. For smaller species like parasitic insects that are specialized to attack one or a group of closely related hosts, have short adult lifespans and discrete generation times, compete directly for limited resources in small, closed arenas and have life histories constrained by host phenology, temporal resource subdivision viavariation in life history may play a critical role in allowing species to coexist by alleviating the negative effects of interspecific competition.
Host plants that promote development of insect herbivores are sometimes less preferred to more toxic plants, which are co‐opted for protection from natural enemies, resulting in higher fitness in communities with strong top‐down control. However, the degree to which variation in growth rate and risk of natural enemy attack drive insect plant preferences is an open question, with little field data available across diverse plant families.
The present study investigated the preference–performance relationship and tritrophic interactions involving the hornworm
Manduca sexta, its natural enemies, and plants in the nightshade family (Solanaceae) using a 2‐year common garden containing 18 wild and domesticated species. The degree to which natural enemy pressure explained field patterns in the laboratory was then tested using targeted assays involving parasitism by the wasp Cotesia congregata.
In the field, the most preferred plants for female oviposition tended to be inversely correlated with the species providing optimal larval growth. Hawkmoths preferred plants in the subgenus
Potatoe, Nicotiana, and Daturacompared with Capsicum, Physalis, and the other Solanumsubgenera. However, larval parasitism by was only significant for hornworms on C. congregata Potatoe/ Daturaand not Nicotiana(i.e. 33% vs. 12% vs. 4% parasitism on Potatoe, Datura, and Nicotiana, respectively). Experimental laboratory rearing confirmed that wasp survival is lower on Nicotianasp. than , which could be driven by nicotine. Solanum lycopersicum
The data obtained in the present study show that the negative preference‐performance relationship in hornworms across solanaceous plants is maintained in part because by utilising noxious food plants
M. sextagains protection against parasitism.