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''Samea multiplicalis'', the salvinia stem-borer moth, is an aquatic moth commonly found in freshwater habitats from the southern United States to
In its native habitat, ''S. multiplicalis'' prefers the water lettuce '' P. stratiotes'' over other aquatic plants for feeding and oviposition, and in its introduced habitat in Australia, it primarily feeds and lays eggs on the water fern '' Salvinia molesta''. ''P. stratiotes'' has a rosette of leaves surrounding a short, central stem and a submerged root system. Leaves are covered in short hairs. ''S. molesta'' plants in Australia are all clones, meaning they are genetically identical. However, there is some phenotypic variation due to differing temperature and nitrogen availability across its range, which is important due to ''S. multiplicalis'' larvae's preference for high-nitrogen food sources.
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...
, as well as in Australia where it was introduced in 1981. Salvinia stem-borer moths lay their eggs on water plants like '' Azolla caroliniana'' (water velvet), '' Pistia stratiotes'' (water lettuce), and ''Salvinia rotundifolia
''Salvinia'', a genus in the family Salviniaceae, is a floating fern named in honor of Anton Maria Salvini, a 17th-century Italian scientist. Watermoss is a common name for ''Salvinia''. The genus was published in 1754 by Jean-François Ségui ...
'' (water fern). Larval feeding on host plants causes plant death, which makes ''S. multiplicalis'' a good candidate for biological control
Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically als ...
of weedy water plants like '' Salvinia molesta'', an invasive water fern in Australia. However, high rates of parasitism in the moth compromise its ability to effectively control water weeds. ''S. multiplicalis'' larvae are a pale yellow to green color, and adults develop tan coloration with darker patterning. The lifespan, from egg to the end of adulthood is typically three to four weeks. The species was first described by Achille Guenée
Achille Guenée (sometimes M.A. Guenée; 1 January 1809 – 30 December 1880) was a French lawyer and entomologist.
Biography
Achille Guenée was born in Chartres and died in Châteaudun.
He was educated in Chartres, where he showed a very e ...
in 1854.
Geographic range
''Samea multiplicalis'' was first observed inBrazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
in 1854, and has since been documented across the southeastern United States, as far west as Louisiana
Louisiana , group=pronunciation (French: ''La Louisiane'') is a U.S. state, state in the Deep South and South Central United States, South Central regions of the United States. It is the List of U.S. states and territories by area, 20th-smal ...
. This region constitutes its native range. In 1981, the moth was introduced in Australia as a potential method of biological control of the water fern, '' S. molesta''. It is now common throughout Queensland
)
, nickname = Sunshine State
, image_map = Queensland in Australia.svg
, map_caption = Location of Queensland in Australia
, subdivision_type = Country
, subdivision_name = Australia
, established_title = Before federation
, established_ ...
and New South Wales
)
, nickname =
, image_map = New South Wales in Australia.svg
, map_caption = Location of New South Wales in AustraliaCoordinates:
, subdivision_type = Country
, subdivision_name = Australia
, established_title = Before federation
, es ...
. In Australia, it has been found to thrive in tropical climates, with slower growth and dispersal in more temperate climates.
Habitat
''S. multiplicalis'' primarily lives on the water plants, ''Azolla caroliniana'' (water velvet), '' Pistia stratiotes'' (water lettuce), ''Salvinia rotundifolia'' (water fern) in their native range, and '' Salvinia molesta'' (a water fern) in Australia. These plants grow to form floating mats on the surface of calm or still bodies of water like ponds, lakes, and slow-moving rivers. ''S. multiplicalis'' can survive within a temperature range of 11-36 °C, however it survives best around temperatures of 30 °C. It requires warm conditions to survive and develop, however steady temperatures above the low 30s cause populations to crash. Moth populations can survive year round in habitats where food resources and adequate temperatures are sustained through the winter.Food resources
Host plant
In its native habitat, ''S. multiplicalis'' prefers the water lettuce '' P. stratiotes'' over other aquatic plants for feeding and oviposition, and in its introduced habitat in Australia, it primarily feeds and lays eggs on the water fern '' Salvinia molesta''. ''P. stratiotes'' has a rosette of leaves surrounding a short, central stem and a submerged root system. Leaves are covered in short hairs. ''S. molesta'' plants in Australia are all clones, meaning they are genetically identical. However, there is some phenotypic variation due to differing temperature and nitrogen availability across its range, which is important due to ''S. multiplicalis'' larvae's preference for high-nitrogen food sources.
Food preferences
Caterpillar
Caterpillars ( ) are the larva, larval stage of members of the order Lepidoptera (the insect order comprising butterfly, butterflies and moths).
As with most common names, the application of the word is arbitrary, since the larvae of sawfly ...
s of the salvinia stem-borer moth feed on several aquatic plants, primarily ''Azolla caroliniana'' (water velvet), ''Pistia stratiotes'' (water lettuce), ''Salvinia rotundifolia'' (water fern), ''Salvinia molesta'' (a water fern), and occasionally ''Eichhornia crassipes
''Pontederia crassipes'' (formerly ''Eichhornia crassipes''), commonly known as common water hyacinth is an aquatic plant native to South America, naturalized throughout the world, and often invasive outside its native range.
Larvae hatch approximately four days after eggs are laid. Larvae have an off-white or pale yellow color during early instars and develop a yellow-green color as they mature. They typically develop through five instars over the course of about two weeks, and male larvae develop faster than females by about two days. In low-
''S. molesta'' is an aquatic plant native to Brazil that is invasive in Australia due to a lack of sufficient herbivory to control the growth of the plant. It has become a common weed in many bodies of water, especially in eastern Australia in Queensland and New South Wales. The water fern grows in expansive mats, potentially crowding out other native aquatic plants and preventing light penetration in water bodies where it grows. Efforts to control ''S. molesta'' began in 1980 with the introduction of the salvinia weevil '' Cyrtobagous salviniae'', which is also native to Brazil. ''S. multiplicalis'' was introduced the following year in 1981 to aid in the biological control of the weed.
Protection while feeding
Often, groups of larvae displaycooperative behavior
Cooperation (written as co-operation in British English) is the process of groups of organisms working or acting together for common, mutual, or some underlying benefit, as opposed to working in competition for selfish benefit. Many animal a ...
when they feed in groups. They collectively construct a silk canopy over their feeding site while they eat, expanding it as they exhaust their current site and move on to new areas of their host plant. This behavior offers protection from predation, decreasing larval mortality.
Larval nutrition
Nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...
is very important nutrient for larval development, especially during the first two instar
An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow o ...
s, so larvae prefer food plants with higher nitrogen content. Higher nitrogen intake correlates with larger larval biomass and faster development, both of which are favored because they decrease larval vulnerability to predation. Additionally, a lack of sufficient nitrogen intake during early development leads to decreased ability to digest and utilize food throughout the rest of the insect's life.
Compensatory feeding
Water lettuce and other aquatic plants tend to have high water content, which dilutes the nitrogen and other nutrients they contain. To account for this, ''S. muliplicalis'' has a higher feeding rate than many other Lepidoptera species. When nitrogen levels are especially low, larvae show compensatory feeding behavior, increasing their already high feeding rate and consuming a larger volume in order to make up for the nutrient deficit. This behavior does not usually mitigate the poor quality food, however, and larvae on nitrogen-depleted host plants still experience slower development and decreased digestive efficiency.Life history
Larvae
Larvae hatch approximately four days after eggs are laid. Larvae have an off-white or pale yellow color during early instars and develop a yellow-green color as they mature. They typically develop through five instars over the course of about two weeks, and male larvae develop faster than females by about two days. In low-nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...
conditions, larvae require a sixth instar and two or three additional days to develop.
Pupae
Caterpillars construct a silk cocoon inside of a leaf petiole on their host plant in order to pupate. Pupation lasts between four and ten days, with females developing faster than males. Time spent in this stage of development is not dependent on larval nutrition.
Adults
After they emerge from their cocoons, adult salvinia stem-borer moths spend the rest of their three- or four-week life span around their host plants, mating and laying eggs. Female moths lay an average of 150 eggs over the course of several days on the surfaces of host plant leaves or among hairs or leaflet structures. Moths prefer the host plant ''P. stratiotes'' for laying eggs due to its structure which provides abundant oviposition surfaces. Moths are not known to oviposit on ''E. crassipes''. Adults are tan with darker markings on both sets of wings and a wingspan of about 20 mm. Adult size is not significantly affected by larval nutrition levels, however insufficient nitrogen during larval development does lead to reduced egg production in female moths.Enemies
Parasites
''S. multiplicalis'' is affected by a number of parasites, most commonly by wasp species of the order Hymenoptera and parasitic flies of the order Diptera, as well as miscrosporidia. Parasitic wasps attack ''S. multiplicalis'' larvae during their first instar and pre-pupal wasps emerge during the caterpillars' last instar, killing their hosts. Parasitism rates are fairly high in some populations, which diminishes their effectiveness at controlling weedy host plants. ''S. multiplicalis'' larvae are parasitized in both their native and introduced ranges by similar species. Parasitism rates remain steady through spring, summer, and fall and decrease slightly during winter months.Interactions with humans
Biological control agent
''S. molesta'' is an aquatic plant native to Brazil that is invasive in Australia due to a lack of sufficient herbivory to control the growth of the plant. It has become a common weed in many bodies of water, especially in eastern Australia in Queensland and New South Wales. The water fern grows in expansive mats, potentially crowding out other native aquatic plants and preventing light penetration in water bodies where it grows. Efforts to control ''S. molesta'' began in 1980 with the introduction of the salvinia weevil '' Cyrtobagous salviniae'', which is also native to Brazil. ''S. multiplicalis'' was introduced the following year in 1981 to aid in the biological control of the weed.
''C. salviniae'' and ''S. multiplicalis''
Since their introduction, the two insects have had different levels of effectiveness; theweevil
Weevils are beetles belonging to the superfamily Curculionoidea, known for their elongated snouts. They are usually small, less than in length, and herbivorous. Approximately 97,000 species of weevils are known. They belong to several families, ...
has proved more useful than the moth at keeping salvinia populations down through intensive feeding. While ''C. salviniae'' and ''S. multiplicalis'' both have similar habitat needs, including common host plants, similar nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...
requirements, and an optimal temperature of 30 °C, ''S. multiplicalis'' populations are highly susceptible to parasites and parasitoids, which prevent the colony growth and dispersal that would be required for effective weed control. ''S. multiplicalis'' actually has a higher rate of reproduction and dispersal than ''C. salviniae'', but infection prevalence still prevents sufficient levels of feeding to significantly affect ''S. molesta'' numbers.
References