Toxic Peptides in Populations of Two Pergid Sawflies, Potential Biocontrol Agents of Brazilian Peppertree.

Determination of the safety of agents prior to release is one of the most important research goals in biological control. In addition to concerns for the safety of non-target plants, determination of the potential toxic properties of new agents needs to be assessed. Numerous phytophagous insects are defended by chemicals against the attack of natural enemies. Some of these defensive compounds could pose an environmental risk if an agent is released. Here, larval populations of two pergid sawflies, Heteroperreyia hubrichi and H. jorgenseni, were analyzed by LC-MS/MS to investigate whether they contain alleged toxic peptides. The first species is a potential candidate for biological control of the invasive weed Brazilian peppertree in Florida and Hawaii. The chemical analyses revealed the presence of the peptides pergidin (Perg), 4-valinepergidin (VPerg), dephosphorylated pergidin (dpPerg), lophyrotomin (LGln and LGlu). The effect of sawfly population for each species was significantly influencing peptide concentration. All peptides occurred at lower concentrations compared with purportedly toxic species of this sawfly family. However, the concentrations of the peptides are of concern for the welfare of wildlife and livestock that would be exposed to these species. These results demonstrate that release of this biological control agent in the invaded range may pose an environmental threat.

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.

Specificity of extrafloral nectar induction by herbivores differs among native and invasive populations of tallow tree.

BACKGROUND AND AIMS: Invasive plants can be released from specialist herbivores and encounter novel generalists in their introduced ranges, leading to variation in defence among native and invasive populations. However, few studies have examined how constitutive and induced indirect defences change during plant invasion, especially during the juvenile stage. METHODS: Constitutive extrafloral nectar (EFN) production of native and invasive populations of juvenile tallow tree (Triadica sebifera) were compared, and leaf clipping, and damage by a native specialist (Noctuid) and two native generalist caterpillars (Noctuid and Limacodid) were used to examine inducible EFN production. KEY RESULTS: Plants from introduced populations had more leaves producing constitutive EFN than did native populations, but the content of soluble solids of EFN did not differ. Herbivores induced EFN production more than simulated herbivory. The specialist (Noctuid) induced more EFN than either generalist for native populations. The content of soluble solids in EFN was higher (2·1 times), with the specialist vs. the generalists causing the stronger response for native populations, but the specialist response was always comparable with the generalist responses for invasive populations. CONCLUSIONS: These results suggest that constitutive and induced indirect defences are retained in juvenile plants of invasive populations even during plant establishment, perhaps due to generalist herbivory in the introduced range. However, responses specific to a specialist herbivore may be reduced in the introduced range where specialists are absent. This decreased defence may benefit specialist insects that are introduced for classical biological control of invasive plants.

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.

Localized Induced Defenses Limit Gall Formation by Eriophyid Mite Against Invasive Lygodium microphyllum (Schizaeales: Lygodiaceae).

A potential barrier to the establishment of weed biological control agents is interference from other management tactics that induce plant defenses. Methods that suppress the weed such as feeding by other biological control agents or mechanical removal are especially disposed to inducing plant defenses and potentially limiting agent establishment. Here, we focused on the invasive weed Lygodium microphyllum (Cav.) R. Br. (Schizaeales: Lygodiaceae, Old World climbing fern) and one of its biological control agents, the mite Floracarus perrepae Knihinicki and Boczek (Acariformes: Eriophyidae). We experimentally induced plant defenses in potted plants via damage or application of jasmonic acid, a hormone typically involved in plant defenses, and measured the responses of the mite in a screenhouse. Localized damage to the pinnae (e.g., leaflets) via cutting or larval feeding from a second biological control agent, Neomusotima conspurcatalis (Warren) (Lepidoptera; Crambidae), reduced F. perrepae gall formation, but not the number of mites per gall. In contrast, damage to rachises (e.g., stems) did not affect galling, likely because plant defense responses were not systemic. Application of jasmonic acid reduced gall formation but not the numbers of mites within galls. Taken together, we found that localized damage interfered with gall formation but not within-gall reproduction. However, these effects on the mite from induced plant defenses are likely short-lived, and therefore interference between management tactics is unlikely to affect F. perrepae establishment and performance.

Advances in Mass Rearing Pseudophilothrips ichini (Hood) (Thysanoptera: Phlaeothripidae), a Biological Control Agent for Brazilian Peppertree in Florida.

Pseudophilothrips ichini is a recently approved biological control agent for the highly invasive Brazilian peppertree in Florida, USA. Prior to approval for field release in 2019, thrips colonies used for host specificity testing were produced and maintained in small cylinders to fit in restricted quarantine spaces. This next segment in the classical biological control pipeline is mass production and distribution of P. ichini. To accomplish this, we developed novel techniques to expand from small colony maintenance to large-scale production. We first quantified the productivity of the small cylinders, each containing a 3.8 L potted plant and producing an average of 368 thrips per generation. Given the amount of maintenance the cylinders required, we investigated larger cages to see if greater numbers of thrips could be produced with less effort. Acrylic boxes (81.5 × 39.5 × 39.5 cm) each contained two 3.8 L plants and produced an average of 679 thrips per generation. The final advancement was large, thrips-proof Lumite® screen cages (1.8 × 1.8 × 1.8 m) that each held six plants in 11.4 L pots and produced 13,864 thrips in as little as 5 wk. Screen cages and cylinders had the greatest thrips fold production, but screen cages required ten times less labor per thrips compared to either cylinders or boxes. The efficiency of these large screen cages ensured sustained mass production and field release capacity in Schinus-infested landscapes. The screen cage method is adapted and used by collaborators, and this will expand the literature on beneficial thrips mass rearing methods.

Community of Bark and Ambrosia Beetles (Coleoptera: Curculionidae: Scolytinae and Platypodinae) Infesting Brazilian Peppertree Treated With Herbicide and the Volatile Tree Response.

Brazilian peppertree, Schinus terebinthifolia Raddi (Anacardiaceae), is one of the most invasive weeds of natural and agricultural areas of Florida, Hawaii, and Texas (USA). Herbicides are the main tool used to manage populations of this weed. Faunal inventories of the insects associated with invasive populations of the weed have mostly listed leaf-feeding phytophagous, pollinator, or predacious species. Among these, bark and ambrosia beetles were collected only once from S. terebinthifolia in the invaded range and there are no reports from the native range. A diverse assemblage of bark and ambrosia beetles, many well-known economic pests of ornamentals, was reared from S. terebinthifolia bolts collected at a restoration site in Florida that had been treated with herbicide (triclopyr ester). A similar collection of beetles was captured on ethanol-baited sticky traps. No beetles emerged from bolts of untreated trees, almost none emerged from those wounded with a machete (3.1% of total), whereas nearly all the beetles collected emerged from bolts that had been treated with herbicide (62.3%) or the combination wounded + herbicide (34.6%). Ethanol was detected from the herbicide and wound + herbicide-treated bolts suggesting this was the attractive kairomone. Abundant amounts of other volatiles were collected from all bolts, especially from the wounded treatment, but no association was detected between volatile emissions and beetle infestation. Further studies are needed to determine whether invasive populations of S. terebinthifolia treated with herbicides constitute reservoirs for pest bark and ambrosia beetles that may spill over onto neighboring ornamental hosts.

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.

Heterapoderopsis bicallosicollis (Coleoptera: Attelabidae): a potential biological control agent for Triadica sebifera.

Native to China, Chinese tallow, Triadica sebifera L. Small (Euphorbiaceae), is an invasive plant in the southeastern United States. The leaf-rolling weevil, Heterapoderopsis bicallosicollis Voss, is a common herbivore attacking this plant in China. To evaluate its potential as a biological control agent of T. sebifera, biology and host specificity of this weevil were studied in China. H. bicallosicollis occurs over a wide, native, geographic range and its immatures successfully develop at 15-35 degrees C, indicating its physiological potential to establish and persist throughout the range of climatic conditions where the target plant grows in the United States. Adults make feeding holes on leaves. Before oviposition, the female makes a sealed leaf roll called a nidus and then lays one to two eggs inside. Eggs, larvae, and pupae develop within nidi, and larvae survive only when they develop inside the nidi. This requirement makes the weevil highly host specific to T. sebifera. In laboratory no-choice tests of 54 species from eight families, adults fed on only 3 plant species, T. sebifera, Sapium chihsinianum S. K. Lee, and Phyllanthus urinaria L. and only oviposited on T. sebifera. These results were confirmed where, in multiple-choice tests, adults only oviposited on T. sebifera. Given that T. sebifera is the only species in the genus Triadica in the United States, the results of this study suggest that H. bicallosicollis is a potential biological control agent of T. sebifera and should be considered to be imported into quarantine in the United States for further tests on native North American species.

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. viridissima's orchid mutualists in Mesoamerica. Aromatic leaves, such as basil, were found to be important surrogate sources of needed fragrance compounds in Florida. The bee's 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.

Compensatory feeding response of the slug Sarasinula plebeia to dietary dilution.

Like many polyphagous herbivores, individuals of Sarasinula plebeia (Fischer) (Soleolifera: Veronicellidae) consume a variety of plant species that may differ in nutritional content. In this study we determined the ability of these slugs to compensate for such variation in diet composition. Dilution with water of an agar-based diet containing commercial guinea pig food or carrot root to obtain dry weights (dw) of 90, 70, 40 and 10% of diet fresh weight (fw), caused immature slugs to consume increasingly more fresh weight of food [as much as 4.7-(guinea pig) to 6.1-fold (carrot) more]. Dry weight consumption and body mass-relative dry weight consumption rate also increased at intermediate dilutions, buth with further dilution, dry weight intake declined despite the greater fresh weight consumption. At each dilution level, slugs fed the guinea pig diet consumed from ca. 5-to 6.4-fold more fresh weight than the carrotfed slugs. The former grew substantially, with their final biomass and body mass-relative growth rate varying curvilinearly with diet % dw. If these slugs had not fed more but instead maintained the same fresh weight consumption as slugs in the 90% dw tretments, without altering food utilization efficiencies, then their biomass gain in the 70, 40 and 10% dw treatments would have been only about 62, 43, and 21%, respectively, of the values actually attained. In contrast, carrot-fed slugs did not grow and were only able to maintain their initial biomass. For each diet, slug tissue water (% fw) was highest in the most diluted treatment but did not differ significantly among the other dilution levels. Approximate digestibility of the carrot diet was highest at intermediate dilution levels (ca. 75% of ingested food was digested and absorbed); for the guinea pig diet, this efficiency declined linearly from about 66% to 59% with increased dilution. For slugs that grew (i.e., those fed the guinea pig diet), effeciences of converting digested (29-52%) and ingested (18-33%) food to dry biomass were both curvilinearly related to diet % dw. Thus, S. plebeia, like many other herbivores, has the capacity to increase food consumption substantially inresponse to reduced dietary nutrient level, allowing the slugs to cope with variable nutrient content in their food plants.

Genetic variation and evolution of secondary compounds in native and introduced populations of the invasive plant Melaleuca quinquenervia.

We examined multivariate evolution of 20 leaf terpenoids in the invasive plant Melaleuca quinquenervia in a common garden experiment. Although most compounds, including 1,8-Cineole and Viridiflorol, were reduced in home compared with invaded range genotypes, consistent with an evolutionary decrease in defense, one compound (E-Nerolidol) was greater in invaded than home range genotypes. Nerolidol was negatively genetically correlated with Cineole and Viridiflorol, and the increase in this compound in the new range may have been driven by this negative correlation. There was positive selection on all three focal compounds, and a loss of genetic variation in introduced range genotypes. Selection skewers analysis predicted an increase in Cineole and Viridiflorol and a decrease or no change in Nerolidol, in direct contrast to the observed changes in the new range. This discrepancy could be due to differences in patterns of selection, genetic correlations, or the herbivore communities in the home versus introduced ranges. Although evolutionary changes in most compounds were consistent with the evolution of increased competitive ability hypothesis, changes in other compounds as well as selection patterns were not, indicating that it is important to understand selection and the nature of genetic correlations to predict evolutionary change in invasive species.

Biology and host range of Tecmessa elegans (Lepidoptera: Notodontidae), a leaf-feeding moth evaluated as a potential biological control agent for Schinus terebinthifolius (Sapindales: Anacardiaceae) in the United States.

During surveys for natural enemies that could be used as classical biological control agents of Schinus terebinthifolius Raddi (Brazilian pepper), the caterpillar, Tecmessa elegans Schaus (Lepidoptera: Notodontidae), was recorded feeding on the leaves of the shrub in South America. The biology and larval and adult host range of this species were examined to determine the insect's suitability for biological control of this invasive weed in North America and Hawaii. Biological observations indicate that the larvae have five instars. When disturbed, the late instar larvae emit formic acid from a prothoracic gland that may protect larvae from generalist predators. Larval host range tests conducted both in South and North America indicated that this species feeds and completes development primarily on members of the Anacardiaceae within the tribe Rhoeae. Oviposition tests indicated that when given a choice in large cages the adults will select the target weed over Pistacia spp. However, considering the many valued plant species in its host range, especially several North American natives, this species will not be considered further for biological control of S. terebinthifolius in North America.

Differential performance of tropical soda apple and its biological control agent Gratiana boliviana (Coleoptera: Chrysomelidae) in open and shaded habitats.

The leaf feeding beetle Gratiana boliviana Spaeth has been released since 2003 in the southeastern United States for biological control of tropical soda apple, Solanum viarum Dunal. In Florida, G. boliviana can be found on tropical soda apple growing in open pastures as well as in shady wooded areas. The objectives of this study were to determine the effect of light intensity on the performance of tropical soda apple and G. boliviana under greenhouse conditions, and to determine the abundance and mortality of G. boliviana in open and shaded habitats. Leaves growing in the shade were less tough, had higher water and nitrogen content, lower soluble sugars, and less dense and smaller glandular trichomes compared with leaves growing in the open. Plants grew slightly taller and wider under shaded conditions but total biomass was significantly reduced compared with plants grown in the open. In the greenhouse, G. boliviana had higher immature survival, greater folivory, larger adult size, and higher fecundity when reared on shaded plants compared with open plants. Sampling of field populations revealed that the overall abundance of G. boliviana was lower but leaf feeding damage was higher in shaded habitats compared with the open habitats. The percentage of eggs surviving to adult was greater in shaded compared with open habitats. The abundance of predators was higher in the open pasture and was positively correlated with the abundance of G. boliviana. These results indicate that not only plant quality but also habitat structure are important to the performance of weed biological control agents.

Differential metabolism of 1,8-cineole in insects.

In order to compare the metabolism of 1,8-cineole in the pyrgo beetle, Paropsisterna tigrina, three other herbivorous insect species, Faex nigroconspersa, Chrysophtharta bimaculata, and Oxyops vitiosa, were fed 1,8-cineole leaf diets. F. nigroconspersa adults excreted predominantly 9-hydroxy-1,8-cineole (36.2% of the volatile constituents) with some 2alpha-hydroxy-1,8-cineole (11.4%). In contrast, larvae excreted predominantly 2alpha-hydroxy-1,8-cineole (27.4%) and smaller proportions of 9-hydroxy-1,8-cineole (5.2%) and 3alpha-hydroxy-1,8-cineole (4.3%). C. bimaculata adults excreted predominantly 3alpha-hydroxy-1,8-cineole (16.5%). Oxyops vitiosa adults, on a lower 1,8-cineole diet, excreted predominantly 2alpha,9-dihydroxy-1,8-cineole (4.2%) and 2alpha-hydroxy-1,8-cineole (3.5%), with smaller proportions of 3alpha-hydroxy-1,8-cineole (1.1%) and 9-hydroxy-1,8-cineole (0.5%). This is the first reported occurrence of a dihydroxycineole as an insect metabolite. Gas chromatographic and mass spectral data for hydroxycineoles are recorded and interspecific metabolite variation discussed.