La polilla de la harina india ( Plodia interpunctella ), también escrita como polilla de la harina india y polilla de la harina india , es una polilla piraloide de la familia Pyralidae . Los nombres comunes alternativos son polilla de la percha , polilla del gorgojo , polilla de la despensa , polilla de la harina o polilla del grano . La polilla de la almendra ( Cadra cautella ) y la polilla de la pasa ( Cadra figulilella ) se confunden comúnmente con la polilla de la harina india debido a sus fuentes de alimento y apariencia similares. La especie recibió su nombre por alimentarse de harina india o harina de maíz, y no se encuentra de forma nativa en la India. Tampoco debe confundirse con la polilla mediterránea de la harina ( Ephestia kuehniella ), otra plaga común de los cereales almacenados.
Las larvas de P. interpunctella ( orugas ) se conocen comúnmente como gusanos de cera . Es importante tener en cuenta que no son la misma especie que los gusanos de cera que a menudo se crían como alimento para animales. Más bien, son una plaga común que se alimenta de granos y que se encuentra en todo el mundo y consume cereales , frutas y productos similares. En Estados Unidos se han realizado esfuerzos sustanciales para controlar los daños que la polilla causa a los cultivos de cereales. [1]
Las larvas de esta especie tienen la capacidad de morder plástico y cartón, por lo que incluso los contenedores sellados pueden resultar infestados. [2] Una vez encontradas, las polillas son difíciles de erradicar. El último estadio larvario también puede viajar largas distancias antes de convertirse en pupa ; por lo que puede desarrollarse un nuevo sitio de infestación lejos del último sitio de pupación. [3] Además de las fuentes de alimento, esta especie puede reproducirse y pupar en la ropa y cualquier fuente de ropa debe ser inspeccionada para evitar la reinfestación.
Plodia interpunctella se encuentra en todos los continentes en hábitats tropicales, excepto en la Antártida. [4] Dentro de los Estados Unidos, la polilla se encuentra más comúnmente en Florida , donde prospera en el hábitat tropical. [3] La polilla vive en una amplia gama de condiciones, lo que la convierte en una plaga persistente . A menudo se encuentra en instalaciones de almacenamiento de alimentos en todo el mundo, específicamente en contenedores o edificios de almacenamiento de granos. [5]
La polilla de la harina india es la única especie viva conocida del género Plodia . Está estrechamente relacionado con los géneros Cadra y Ephestia , que incluyen otras especies de plagas como E. kuehniella , también conocida como "polilla de la harina". [6] [7]
La especie ha sido descrita bajo varios sinónimos menores , que ocasionalmente todavía pueden encontrarse en fuentes no entomológicas . [7]
El nombre común de esta especie, "polilla india de la harina", fue acuñado por Asa Fitch , un entomólogo empleado por el estado de Nueva York en el siglo XIX. En un informe publicado en 1856, Fitch analizó la especie y señaló que se había observado que las larvas infestaban almacenes de harina de maíz , que en ese momento se conocía como "harina india". [8]
Los adultos miden entre 8 y 10 milímetros ( 5 ⁄ 16 - 13 ⁄ 32 pulgadas) de largo con 16 a 20 milímetros ( 5 ⁄ 8 - 13 ⁄ 16 pulgadas) de envergadura. Los dos tercios distales de sus alas anteriores son generalmente de color marrón rojizo con un brillo cobrizo. También pueden ser bronce o gris oscuro. Las partes más proximales de las alas son de color amarillo grisáceo o blanco grisáceo, con una banda oscura en la intersección entre las regiones proximal y distal. Las alas traseras, en general, son uniformemente grises. [9]
Los huevos de la polilla de la harina india son blancos, ovados y muy pequeños. Es difícil verlos a simple vista. Las larvas recién nacidas son igualmente difíciles de ver. En su mayoría son de color blanquecino, tienen cabezas marrones y se desarrollan a lo largo de cinco a siete estadios larvales . Cuando estas larvas maduran, miden entre 12 y 14 milímetros ( 15 ⁄ 32 – 9 ⁄ 16 pulgadas) de largo. Las larvas también tienen tres pares de patas cerca de la cabeza y cinco pares de patas protuberantes que sobresalen del abdomen. Las patas ayudan a las larvas a moverse largas distancias para encontrar sitios de pupación. [9]
Las polillas de la harina india se alimentan de plantas, cereales y otros productos alimenticios humanos.
Las polillas se alimentan de muchos alimentos de origen vegetal, incluidos alimentos secos para mascotas (a base de plantas), alpiste, cereales, mezclas para sopas, pan, pasta, arroz, harina, especias, frutas secas y nueces. Hay pruebas sólidas de que el trigo del norte de Manitoba favorece el desarrollo de la polilla. Otras dietas óptimas incluyen pasas, maíz amarillo americano y almendras. Por otro lado, el maní y la harina de maíz dan como resultado un tiempo de desarrollo más prolongado para las polillas. [10]
También se sabe que las polillas de la harina de la India canibalizan larvas, pero esto a menudo conduce a infecciones por granulosis viral que se propagan a través de una población de polillas de la harina de la India. Las larvas sanas se recogen con más frecuencia que las no saludables para el canibalismo. [11] Parece que no hay discriminación de parentesco y las orugas pueden comerse a los hermanos. [12]
Aunque las polillas de la harina india generalmente no migran largas distancias, sí realizan vuelos de larga distancia en busca de alimento. Estos vuelos tienen lugar durante las horas del crepúsculo, durante las cuales la luz azul (400 a 475 nm) en lugar de la luz ultravioleta (10 a 400 nm) es dominante y atrae a las polillas. El papel de la luz azul en el comportamiento de búsqueda de alimento de la polilla india de la harina se ha aprovechado recientemente como una forma de control de plagas, ya que resulta atractiva para la polilla. [13]
Por lo general, el ciclo de vida de una colonia de polilla de la harina india comienza en un lugar donde hay granos. La temperatura dentro de un contenedor de granos debe exceder los 50 °F (10 °C). Los huevos de la polilla son de color blanco grisáceo y tienen una longitud de entre 0,3 y 0,5 milímetros ( 1 ⁄ 64 y 3 ⁄ 128 pulgadas). Los huevos se pueden poner directamente en la fuente de alimento de forma individual o en grupos de entre 12 y 30. Una hembra madura puede poner entre 100 y 300 huevos a la vez. [1]
Larvae begin to hatch in approximately two to fourteen days. The larvae have between five and seven instars. Newly hatched larvae feed on grain while more mature larvae feed on grain germ. The larvae are an off-white color, but can be pink, brown, or greenish. They are about 12 mm long and have prolegs for movement. Fully-grown larvae are able to spin webs and leave silk threads in their path of travel. Mature larvae that make silk also make threaded cocoons.[1]
The pupae are often seen on grain surfaces and on the walls of grain bins. The adults emerge in four to ten days. They then mate and the cycle begins again.[1] The entire life cycle of this species ranges between 30 and 300 days. A typical life cycle is 50 days. Under optimal conditions a life cycle can be as short as 28 days but cooler winter months prohibit this. Seven to nine generations of moths can live in a year.[3][9]
Diapause is defined as a delay in animal development due to certain external factors[14] and can end once the adverse environmental conditions wear off. The duration of diapause can vary in Indian-meal moths. Diapause is especially prevalent late in the breeding season. During the egg stage, if the temperature of the moth's environment exceeds 25 °C (77 °F), it can cause a delay in hatching. In the moth's early larval stage, temperatures of below 20 °C (68 °F) can cause a similar diapause. Different strains of P. interpunctella have differing tendencies to enter diapause.[15]
Indian-meal moths are developing a resistance to many kinds of biological agents, such as the granulosis virus. Use of pest control agents can cause resistance to these agents to be selected for in populations of Indian-meal moths. In populations exposed to the granulosis virus, it was found that the moths were 96 times more resistant to the virus. This led to the prohibition of many such biological agents.[18]
Regulations prevent the use of many pesticides near food sources so these pests are highly suitable for control with natural predators.[19]
Females mate multiple times, so sperm competition could be an important aspect of male-male competition for being reproductively successful. Males have a limited number of sperm and allocate it depending on various factors. Male Indian-meal moths ejaculate a greater amount of sperm to females that have mated multiple times previously. This is to ensure a greater chance of success in sperm competition in the females' storage organs. Males also ejaculate more sperm when mating with a younger female.[20]
The most common type of competition in Indian-meal moths is due to a lack of food. This competition can change the timing of male and female emergence, reducing the chance of early males finding females to mate with, which could encourage emigration.[21] This is considered a form of male-male competition because males that emerge at an appropriate time are more likely to be reproductively successful with the surrounding females.
Males are also involved in finding pupation sites. If the larvae do not find pupation sites in the food layer, they may wander long distances to find one. This competition to find a pupation site affects males more than it does females, it indirectly impacts females as well because it results in a delayed population of males to mate with.[21]
In the Indian-meal moth, mating occurs a few days after the adult moth emerges from the silk cocoon. Mating rituals are largely limited to pheromones release by the female. There are four identified (via mass spectrometry techniques) primary pheromones in the female pheromone blend: (Z,E)-9,12-tetradecadienyl acetate, (Z,E)-9,12-tetradecadienal, (Z,E)-9,12-tetradecadienol, and (Z)-9-tetradecenyl acetate. These pheromones are attractants to male moths. Removing any one component of the blend reduces the activity of the pheromone and the number of males attracted. Other components of the pheromone blend are also known but their functions are unclear. It has been suggested the reason for having so many components to the pheromone is that it ensures species specificity.[22]
Male moths also release pheromones. After approaching the female from the back, the male releases a pheromone from wing glands located at the base of each forewing. These pheromones induce the female to remain stationary in the acceptance posture (raised abdomen between wings) which facilitates copulation.[23]
Indian-meal moths are known to mate multiple times. For males, it is vital to ensure paternity after copulation. To ensure this trait, males who mate with a female first (before any other males) will insert a large package of spermatophore, accessory gland fluids, and nutrients into the bursa copulatrix of the female during copulation. Other donations after the first mating are smaller in size. Even so, there is no change in postcopulatory behavior in females after this large donation (with respect to pheromone production and calling behavior).[24]
It has been observed in many insects that vital resources are tracked using odor plumes.[25] For the Indian-meal moth these odors have other effects as well. The Indian-meal moth's fecundity and fertility was found to be enhanced in the presence of the odor of vital nutrients. This effect is thought to be genetic since it is not related to parental generations or previous experiences in the lifetime of the moth. Females also show a strong preference towards laying their eggs near the site of the odor. It was observed that without antennae, this effect is lost, suggesting that there are olfactory receptors in the antennae.[26]
The Indian-meal moth often takes part in interspecific courtship especially with the almond moth (Cadra cautella). Successful mating between the species does not happen due to multiple isolation mechanisms. The main mechanism that has been identified is the male sex pheromone. This pheromone is a strong species recognition signal. It allows the almond moth to differentiate between members of its own species and members of the Indian-meal moth species. There are also mechanical barriers to insemination that render the species incompatible. Their courtship behaviors are also relatively incompatible. Thus, copulation rarely occurs.[27]
Even when courtship does continue to a later stage, the female of the other species rejects the male due to the wrong pheromone being released at the wrong time from scent scales. Even with these fail safes, some male almond moths are still excited by Indian-meal moth females. They may be able to successfully copulate, but insemination is not possible.[27]
Indian-meal moth larvae can infest a wide range of dry foodstuffs of vegetable origin, such as cereal, bread, pasta, rice, couscous, flour, spices, dried fruits, and nuts. More unusual recorded foods include crushed red pepper, chocolate and cocoa beans, coffee substitute, cookies, dried mangelwurzel, and even the toxic seeds of jimsonweed (Datura stramonium). They have also been known to infest commercial pet food, such as cracked corn used for bird feed. They often leave webbing in the food they infest.[3][28]
After larvae or moths have been found, it is important to throw out all food sources not in very tightly sealed containers. Moth larvae can chew through plastic bags and thin cardboard, so even unopened packages may become infested.[2] They are also notoriously difficult to get rid of[citation needed], and can crawl on ceilings and spin cocoons in rooms other than where they hatched. Last instar larvae are able to travel significant distances before they pupate. When seeking the source of an infestation, the search thus cannot be limited to the immediate area where pupae are discovered.[3] Pantry moths can use clothing (remaining hidden) to reproduce and pupate, so it is important to inspect any source of clothing material.
None of the stages of the organism (eggs, larvae, adults) are temperature tolerant and can be killed by a week of freezing or by brief heating in a microwave or conventional oven when such treatment is practical.[9] Scrubbing infested areas with a mixture of soap and water or vinegar is also effective.[29]
Nontoxic traps are available to monitor outbreaks. One type of trap is a triangular box with a pheromone lure and sticky walls inside. These traps are known as pheromone traps. Male moths are attracted by the female pheromone (the lure) and stick against the sticky walls inside the box.[30]
The efficiency of traps is doubtful as they only capture males, and usually only a fraction of them, while adult females, eggs and larvae are unaffected, enabling a possible reinfestation. It is most effective to treat the infestation by eliminating the source and any affected food items, interrupting their mating processes, and repelling them from the areas where dried food and grains are kept. It is recommended to first eliminate the source of infestation followed by larvae, eggs, and eventually moths.[31]
The caterpillars are parasitized by Habrobracon hebetor, a braconid wasp which is a potential biological control agent.[32]
Additionally, blue to violet light can be very effective in drawing moths out, which suggests that the deployment of violet light could become another pest control tactic for these moths.[13]
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