Gregory S. Wheeler

ORCHID BEES DON'T NEED ORCHIDS: EVIDENCE FROM THE NATURALIZATION OF AN ORCHID BEE IN FLORIDA

Almost 200 species of orchid bees are the exclusive pollinators of nearly 700 specialized orchids in the neotropics. This well-known mutualism involves orchids, called perfume orchids, which produce species-specific blends of floral fragrances, and male orchid bees, which collect and use these fragrance compounds during their courtship. We report here the naturalization of an orchid bee, Euglossa viridissima, in southern Florida, USA, where perfume orchids are absent. Chemical analysis of the contents of the fragrance storage organs in the hind tibias of 59 male bees collected in Florida identified 55 fragrance compounds, including 27 known from the perfumes of nine species of E. viridissimas orchid mutualists in Mesoamerica. Aromatic leaves, such as basil, were found to be important surrogate sources of needed fragrance compounds in Florida. The bees ability to live and become abundant in the absence of its orchid mutualists suggests that the orchid bee-perfume orchid mutualism may be facultative for the bees, even though it is obligatory for the orchids. This invasive bee visits and potentially pollinates the flowers of many plants in Florida, behavior that could promote the abundance of selected exotic and native species.

Lower resistance and higher tolerance of invasive host plants: biocontrol agents reach high densities but exert weak control

Invasive plants often have novel biotic interactions in their introduced ranges. Their defense to herbivory may differ from their native counterparts, potentially influencing the effectiveness of biological control. If invasive plants have decreased resistance but increased tolerance to enemies, insect herbivores may rapidly build up their populations but exert weak control. Moreover, resource availability to plants may affect the efficacy of biological control agents. We tested these predictions using Chinese tallow tree (Triadica sebifera) and two specialist herbivores (Heterapoderopsis bicallosicollis and Gadirtha inexacta) that are candidates for biological control. We performed a pair of field common garden experiments in China in which Triadica seedlings from the native or introduced range were grown in low or high light conditions and subjected to different levels of herbivory by each herbivore in a factorial design. We found that Heterapoderopsis achieved greater densities on tallow trees from the introduced range or when trees were grown in high light conditions. When Gadirtha was raised in the lab on tallow tree foliage we found that it performed better (larger pupal size) when fed foliage from introduced populations. However, introduced populations generally had greater herbivore tolerance such that the impact of each agent on plant performance was lower than on native populations despite higher herbivore loads. Tallow trees grew more slowly and achieved smaller sizes in lower light levels, but the impact of biological control agents was comparable to that found for higher light levels. Plants from introduced populations grew larger than those from native populations in all conditions. Our results suggest that reduced resistance and increased tolerance to herbivory in introduced populations may impede success of biological control programs. Biological control practitioners should include plants from the introduced range in the prerelease evaluation, which will help predict insect impact on target weeds.

Brazilian peppertree (Schinus terebinthifolius) in Florida and South America: evidence of a possible niche shift driven by hybridization

Brazilian peppertree (Schinus terebinthifolius Raddi, Anacardiaceae) was introduced into Florida from South America in the 1800s and commercialized as an ornamental plant. Based on herbaria records and available literature, it began to escape cultivation and invade ruderal and natural habitats in the 1950s, and is now considered to be one of Florida’s most widespread and damaging invasive plants. Historical records and molecular evidence indicate that two genetic lineages of Brazilian peppertree were established in Florida, one in Miami on the east coast and a second near Punta Gorda on the west coast. Since arriving, the distributions of these two types have greatly expanded, and they have extensively hybridized. Principal component analysis and reciprocal niche fitting were used to test the equivalency of climatic niches of the Florida populations with the climatic niches of the two South American chloroplast haplotype groups which established in Florida. Both approaches indicated a significant shift in niches between the parental populations in the native range and the invasive populations in Florida. The models, however, closely predicted the areas of initial establishment. We hypothesize that (1) Brazilian peppertree was able to gain an initial foothold in Florida due to niche similarity and (2) the current dissimilarity in native and exotic niches is due to hybridization followed by rapid selection of genotypes adapted to Florida’s climate. In addition, to examine the potential consequence of the introduction of additional genetic diversity from the native range on invasion success, a niche model constructed with occurrences of all native genotypes was projected onto the continental United States. The result of this test indicated that under such an event, the potential invasive range would greatly expand to cover most of the southeastern USA. Our study suggests that multiple introductions from disjunct regions in the native range can facilitate invasion success.

Natural Enemies of Brazilian Peppertree (Sapindales: Anacardiaceae) from Argentina: Their Possible Use for Biological Control in the USA

ABSTRACT Brazilian peppertree (Schinus terebinthifolius Raddi, Anacardiaceae) is a perennial tree native to Argentina, Brazil, and Paraguay. The plant was introduced into the USA before 1900. Originally grown as an ornamental, Brazilian peppertree is now considered an noxious plant in Hawaii and Florida, where it is ranked among the most important threats to biodiversity in natural areas. Recent surveys conducted in northeastern Argentina recovered one fungus associated with distorted leaves and 36 phytophagous insects collected on Brazilian peppertree. A leaf-feeding notodontid moth, a new species of gracillariid leaf blotch miner, and a stem-boring weevil have been selected for further studies to determine their potential as biological control agents of Brazilian peppertree in the USA. The results of these surveys are summarized herein and descriptions are included of the insects that are considered most promising for biological control of this weed.

Compensatory responses of Samea multiplicalis larvae when fed leaves of different fertilization levels of the aquatic weed Pistia stratiotes

Compensatory responses of caterpillars fed low quality food include increased consumption and utilization of essential nutrients. Information about an insects responses to nutritional challenges from their host plants could benefit weed biological control efforts in the selection and establishment of new agents. The target weed, Pistia stratiotes L. (Araceae) is a floating aquatic plant that has relatively low nitrogen levels which are further diluted with high water content. Efforts to establish the insect Spodoptera pectinicornis (Hampson) (Lepidoptera: Noctuidae) for biological control of P. stratiotes could benefit by examining the nutritional responses of a similar widely established lepidopteran species, Samea multiplicalis (Guenèe) (Lepidoptera: Pyralidae). Larvae of this species were fed leaves of P. stratiotes plants that had been fertilized (NPK) at high and low rates. The leaves of the fertilized plants had a 4.3‐fold increase in nitrogen (dry weight) and a 1.6‐fold increase in water content. The results suggest that no compensatory increases occurred in larvae fed leaves from the low fertilized plants as no changes were found in fresh mass consumption or nitrogen utilization efficiency. Consequently, development time from second‐third instars to pupation was delayed about 3 days compared with larvae fed the high nitrogen leaves. Furthermore, consumption of nitrogen was only 30% and its accumulation into larval tissues was only 60% compared with the larvae fed the high fertilized leaves. The resulting larvae had both a final biomass and a growth rate that were reduced by 40%. Regardless of plant fertilizer level, the larvae fed at a rate 5–10 times greater than that of similar lepidopteran species consuming either low or high quality diets, suggesting that the S. multiplicalis larvae may be functioning at their biological limit for ingesting food.

Hybrid Vigor for the Invasive Exotic Brazilian Peppertree (Schinus terebinthifolius Raddi., Anacardiaceae) in Florida

How can successful invaders overcome reduced genetic variation via small founder population sizes to persist, thrive, and successfully adapt to a new set of environmental conditions? An expanding body of literature posits hybridization, both inter- and intraspecific, as a driver of the evolution of invasiveness via genetic processes. We studied Brazilian peppertree (Schinus terebinthifolius), a tree species native to South America that is a successful invader throughout Florida. The tree was introduced separately to the east and west coasts of Florida more than 100 years ago from genetically distinct source populations. We conducted a common garden experiment to compare the early life-stage performance of hybrids versus their progenitors. We hypothesized that hybrids would outperform their progenitors due to the positive genetic effects of intraspecific hybridization (i.e., hybrid vigor). Hybrid seeds germinated at higher rates than eastern seeds. Over the 8-mo experiment, a greater proportion of hybrid seedlings survived than did western seedlings, and hybrids attained greater biomass than the western types. The cumulative hybrid advantage of both seed germination and seedling survival led to the establishment of nearly 45% more hybrid seedlings versus either progenitor. Documenting fitness advantages for hybrids over their progenitors is a requisite finding to consider hybridization as a factor in the success of invasive species.

Molecular evidence of hybridization in Florida’s sheoak (Casuarina spp.) invasion

The presence of hybrids in plant invasions can indicate a potential for rapid adaptation and an added level of complexity in management of the invasion. Three Casuarina tree species, Casuarina glauca, Casuarina cunninghamiana and Casuarina equisetifolia, native to Australia, are naturalized in Florida, USA. Many Florida Casuarina trees are considered unidentifiable, presumably due to interspecific hybridization. We collected tissue from over 500 trees from Australia and Florida and genotyped these using amplified fragment length polymorphisms. Our goal was to determine the exact identity of the Florida species, including any putative hybrid combinations. In Australia, we found high assignment values to the three parental species, and no evidence of hybridization. In Florida, we found many trees with strong assignment to any one of the three species, as well as 49 trees with assignment values intermediate to C. glauca and C. equisetifolia, suggesting hybridization between these species. One population of 10 trees had assignment values intermediate to C. cunninghamiana and C. glauca, suggesting additional hybridization. For 69 of these putative hybrid and parental types, we sequenced a low‐copy intron of nuclear G3pdh, and these sequences indicated that some Florida trees contain heterozygotic combinations of C. glauca and C. equisetifolia haplotypes. The presence of novel hybrids in the Florida invasion may enhance evolution of invasive traits in these species. Novel Casuarina hybrids in Florida have no coevolutionary history with any insects or diseases, which may be problematic for biological control efforts.

Ecology and management of sheoak (Casuarina spp.), an invader of coastal Florida, U.S.A.

Abstract The Casuarina spp. are invasive plants in Florida that threaten biological diversity and beach integrity of coastal habitats. The trees include three species and their hybrids that aggressively invade riverine and coastal areas. Of the three species, C. equisetifolia and C. glauca are highly salt tolerant and widespread in coastal areas. The third species, C. cunninghamiana, invades riverine habitats. These species pose dangers to both the environment and public safety. The environmental damage includes interfering with nesting by endangered sea turtles, American crocodiles, and the rare swallow-tailed kite. Additionally, allelochemical leachates reduce germination and establishment of native vegetation. Casuarina-infested beaches are more prone to sand loss and erosion. Moreover, with shallow roots and tall canopies, they are among the first trees to fall in high winds and as such restrict evacuation efforts during hurricanes. Control of these species is mostly with herbicides, requiring repeated applications and monitoring. One of the most cost-effective means of controlling these invasive species would be with classical biological control. Australian surveys for potential biological control agents began in 2004, resulting in the discovery of several promising candidates. These include seed-feeding torymid wasps, defoliating caterpillars and weevils, leaf tip gall-formers from cecidomyiid midges, and sap-feeding psyllids. Continued work is needed to determine the suitability of these species for biological control. Despite conflicts of interest expressed by some homeowners and the agricultural industry who value the trees for shade and windbreaks, there are good prospects for safe and effective biological control of these invasive species.

Dietary influences on terpenoids sequestered by the biological control agent Oxyops vitiosa: effect of plant volatiles from different Melaleuca quinquenervia chemotypes and laboratory host species.

The weevil Oxyops vitiosa is an Australian species imported to Florida, USA, for the biological control of the invasive species Melaleuca quinquenervia. The larvae of this species feed on the leaves of their host and produce a shiny orange secretion that covers their integument. Previous results indicated that a major component of this secretion, viridiflorol, is sequestered from the host plant and repels a generalist predator, the red imported fire ant, Solenopsis invicta. When the larvae fed on a different chemotype of M. quinquenervia, which lacked viridiflorol but was rich in a different sesquiterpene, (E)-nerolidol, similar protection occurred. Solvent washes of these larvae indicated that (E)-nerolidol was sequestered from M. quinquenervia leaves and repelled S. invicta workers when applied to dog food baits at physiological concentrations (17.5, 35.0, and 52.5 μg/mg). Additionally, β-caryophyllene also repelled S. invicta workers when applied to dog food baits at concentrations that approximated those in the O. vitiosa larval secretions (3.5 and 35 μg/mg). When the O. vitiosa larvae were fed leaves from laboratory hosts (nonfield hosts), similar repellent activity was found. This activity was traced to several of the same compounds (e.g., 1,8-cineole, viridiflorol) found to be active in their field host M. quinquenervia. These weevil larvae are opportunistic, sequestering the primary terpenoids in their host leaves that confer antipredator activity.

Facilitation and inhibition: changes in plant nitrogen and secondary metabolites mediate interactions between above-ground and below-ground herbivores.

To date, it remains unclear how herbivore-induced changes in plant primary and secondary metabolites impact above-ground and below-ground herbivore interactions. Here, we report effects of above-ground (adult) and below-ground (larval) feeding by Bikasha collaris on nitrogen and secondary chemicals in shoots and roots of Triadica sebifera to explain reciprocal above-ground and below-ground insect interactions. Plants increased root tannins with below-ground herbivory, but above-ground herbivory prevented this increase and larval survival doubled. Above-ground herbivory elevated root nitrogen, probably contributing to increased larval survival. However, plants increased foliar tannins with above-ground herbivory and below-ground herbivory amplified this increase, and adult survival decreased. As either foliar or root tannins increased, foliar flavonoids decreased, suggesting a trade-off between these chemicals. Together, these results show that plant chemicals mediate contrasting effects of conspecific larval and adult insects, whereas insects may take advantage of plant responses to facilitate their offspring performance, which may influence population dynamics.