VIRUS ENTOMOPATOGEN Lanjutan By irda Safni Baculoviridae Granulosis

VIRUS ENTOMOPATOGEN (Lanjutan) By irda Safni

Baculoviridae: Granulosis viruses (GV)

Poxviridae: Entomopox Viruses NPV GV GV NPV

Poxviridae: Entomopoxvirus § Member of the family of Poxviridae has a wide host, including vertebrates and invertebrates. §Chicken pox and Small pox virus belong to this family. § The show allantoid – to brick-shaped virions, occluded within ovoid OBs called Spheroids. § Entomopoxvirus has been isolated from 27 orthopterans, lepidopterans, dipterans and coleopterans. § The subfamily Poxvirinae includes three genera, i. e. Entomopoxvirus A, Entomopoxvirus B, and Entomopoxvirus C § Entomopoxvirus A infects only coleopteran species; Entomopoxvirus B infects lepidopteran and coleopteran species; Entomopoxvirus C infects only dipteran species. § The fourth group, group D, has been proposed by ICTV whivh only attacks hymenopterans.

Poxviridae: Entomopoxvirus Anomala cuprea (Coleoptera) larvae infected with an entomopoxvirus show the symptoms of the infection such as a whitish appearance and underdevelopment (left, infected larva; right, healthy one).

Ascoviridae: Ascovirus § A few species of Ascovirus has been isolated only from insects, specifically from Lepidopterans (Noctuidae). § Enveloped virions of ascoviruses are bacilliform, ovoid or allantoid in shape, and occluded within vesicle-like OBs. An ascovirus-infected caterpillar

Structure of Ascovirus virions

Ascoviridae: Ascovirus Lifecycle Ø Ascovirus establishes in the Helicoverpa population through springsummer. Ø The disease is transmitted from caterpillar to caterpillar by wasps (such as Microplitis). Ø Ascovirus could be transmitted directly from one caterpillar to another by spitting - for example, when caterpillars encounter each other on the plant. Ø When ascovirus particles enter the caterpillar´s body they multiply in tissue cells, eventually infecting the haemolymph (blood). This causes the haemolymph to change from clear to milky. The caterpillar stops eating, but may not die for several days or weeks, surviving in a lethargic state.

Ascoviridae: Ascovirus symptoms § In cases where a Microplitis wasp has both parasitised a caterpillar and infected it with ascovirus, the symptoms seen are those of the disease rather than of the parasitoid. When ascovirus kills the caterpillar, it also kills the developing Microplitis larva. § Caterpillars infected with ascovirus will generally stop eating within two days. They stop growing, but can live for weeks in a lethargic state before they die. § The blood of an ascovirus-infected caterpillar is white and creamy, whereas the blood of a healthy caterpillar is clear. Blood colour gives the best diagnosis in the laboratory and can be tested by splitting or pricking the caterpillar.

Iridoviridae: Iridovirus § The viral structure is non-enveloped, non-occluded, isocahedral viral particles. § Viral particles are organized into crystalline arrays. Light reflected from such arrays interferes with incident light, resulting in the characteristic iridescent colors that are the most obvious sign of patent infection. § The small iridovirus tend to display colors from violet to turquoise.

Iridoviridae: Iridovirus § Although some iridoviruses infect frogs and fishes, those infecting insects belong to two genera: Iridovirus, whose viral particles fluctuate between 120 to 130 nm in size. § They mostly infect arthropods, particularly insects, in damp or aquatic habitats worldwide (see complete list of invertebrate hosts. § They are highly infectious by injection but have low infectivity by ingestion. § Horizontal transmission can occur by cannibalism or predation of patently infected individuals, or the virus may even be vectored by nematodes and parasitoid wasps that introduce viral particles into the host insect during the act of penetration or oviposition.

Iridoviridae: Iridovirus infected (blue) larva of Aedes aegypti next to a healthy larva.

Polydnaviridae § Polydnaviridae only infects endoparasitic Hymenoptera. § Member of this family show non-occluded, ovoid virions, containing multipartite ds. DNA § ICTV recognizes two genera within this family, including Ichneovirus and Bracovirus.

Life cycle of of parasitoid wasps and Polydnaviruses (PDVs) parasitizing a lepidopteran larval host

Life Cycle of Insect Virus Generalized life-cycle of insect viruses. Figure credit: Jim Mc. Neil, Department of Entomology, Penn State University.

v Virus particles are usually found on the surface of plants or in the soil. v Insects become infected by consuming plant material with viral particles on the surface, although some pests of low-growing plants can be infected by contact with the soil. v Virus infection begins in the insect’s digestive system but spreads throughout the whole body of the host in fatal infections. v The body tissues of virus-killed insects are almost completely converted into virus particles. v The digestive system is among the last internal organ system to be destroyed, so the insects usually continue to feed until they die. Infected insects look normal until just prior to death, when they tend to darken in color and behave sluggishly. v They often develop more slowly than uninfected individuals.

v Most virus-infected insects die attached to the plant on which they feed. v Virus-killed insects break open and spill virus particles into the environment. These particles can infect new insect hosts. v Because of the destruction of the internal tissues, dead insects often have a “melted” appearance. v The contents of a dead insect can range from milky-white to dark brown or black. v While natural virus outbreaks tend to be localized, virus particles can be spread by the movement of infected insects, the movement of predators such as other insects or birds that come into contact with infected insects, or non-biological factors like water run-off, rain-splash or air-borne soil particles.

v Many virus-infected insects also climb to higher positions on their host plant before they die, which maximizes the spread of virus particles after the insect dies and disintegrates. v The number of virus infection cycles within a growing season depends heavily on the insect’s life cycle. v Insect pests with multiple generations per season or longer life cycles can be more heavily impacted by virus outbreaks since there is a greater opportunity for multiple virus infection cycles within a growing season.

Advantages and Disadvantages of Insect Viruses for Controlling Pests Advantages ØInsect viruses are unable to infect mammals, including humans, which makes them very safe to handle. Most insect viruses are relatively specific, so the risk of non-target effects on beneficial insects is very low. ØMany viruses occur naturally and may already be present in the environment. Even in cases where they are applied, successful infections can perpetuate the disease outbreak making repeat applications within a season unnecessary.

Disadvantages ØMost insect viruses take several days to kill their host insect, during which the pest is still causing damage. Insect death is also dose dependent, and very high doses are often necessary for adequate control. As insects age, they can become less susceptible to virus infection, so viruses are usually only effective against early larval life stages. ØAlthough viruses can persist in the environment for months or years, exposed virus particles, like those on the surface of plants, are quickly inactivated by direct sunlight or high temperatures, which can limit their persistence within a given season. Also, some agricultural practices can reduce persistence between seasons, such as tillage, which buries virus particles in the soil.

Suggestions for application of insect viruses v Viruses are usually not “stand alone” solutions to an insect pest problem, but are most effective in conjunction with other management strategies. v Insect viruses are fairly specific, be sure that the target pest is correctly identified. v Carefully scout fields before application and apply virus when the target pests are young but actively feeding.

v. Apply virus to maximize the longevity and effectiveness of virus particles: • Thoroughly coat plants to maximize coverage. Young plants can even be dipped in a solution of virus particles to completely cover the leaf area. • Apply in the morning or evening or on cloudy days when degradation from sunlight is reduced. • Avoid applying on rainy days, as rain will wash virus particles off the leaf surfaces. • Use formulations with ultraviolet (UV) light blockers and sticking agents to increase longevity. • Using mixed cropping and reduce soil disturbance after application. These help increase the persistence of virus particles in the system and may lead to better control within and between growing seasons.

TERIMA KASIH