Tag Archives: plant pests

Friday Fellow: Cuban Laurel Thrips

by Piter Kehoma Boll

Last week I presented the magnificent Chinese banyan Ficus microcarpa. Today I’m bringing a little insect that loves it but is not loved in return, the Cuban laurel thrips, Gynaikothrips ficorum.

As its name suggests, the Cuban laurel thrips is a thrips, i.e., an insect of the order Thysanoptera. Adults of this species measure about 3 mm in length and have a black and elongate body and two pairs of thin wings that fold over the dorsum when at rest. Its mouth parts, as typical of thrips, are asymmetrical, with a reduced right mandible and a developed left mandible that it uses to cut the surface of plants in order to suck its juices. It is, therefore, a plant pest.

Adult Cuban laurel thrips in Hong Kong. Photo by iNaturalist user wklegend.*

The Cuban laurel thrips prefers to feed on juices of fig trees, such as the Chinese banyan from last week. It’s common name, though, is a reference to another fig species, Ficus retusa, commonly known as the Cuban laurel. Both fig trees, as well as the thrips itself, are native from Southeast Asia. Other, less common host plants include Citrus trees and orchids. They prefer to feed on young, tender leaves, and cause dark, usually purplish red dots, on the leaf’s surface. It is common for the leaf to curl and become hard, eventually dying prematurely. Although most infestations do not cause serious damage to the plant’s development, the curling of the leaves can reduce a plant’s ornamental value.

Ugly curled leaves caused by the thrips’ infestation in New Zealand. Photo by Stephen Thorpe.*

The reproduction of the Cuban laurel thrips is basically constant, so that several generations occur across one year. The adults take advantage of the curled leaves produced by their feeding behavior and use them as a protection to put their eggs. The immature stages, after hatching, remain inside the shelter provided by the curled leaf. They are transparent in the first two instars and then become light yellow. Only the last, adult stage, is black.

When you open the leaf, you can find a whole family. Here you can see the eggs (small white grains) and several immature specimens in different stages. Photo by James Bailey.*

Since the Cuban laurel thrips makes ornamental plants ugly, humans are always trying to find ways to kill them, especially by using pesticides or, sometimes, natural predators of the thrips. But the little insect can also fight back. When the thrips accidentally fall on people’s bodies, they tend to bite, most likely by accident, but this can end up causing a serious and annoying itch. That’s the price for messing with them.

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References:

Denmark HA, Fasulo TR, Funderburk JE (2005) Cuban laurel thrips, Gynaikothrips ficorum (Marchal) (Insecta: Thysanoptera: Phlaeothripidae). DPI Entomology Circular 59

Paine TD (1992) Cuban Laurel Thrips (Thysanoptera: Phlaeothripidae) Biology in Southern California: Seasonal Abundance, Temperature Dependent Development, Leaf Suitability, and Predation. Annals of the Entomological Society of America 85(2): 164–172. doi: 10.1093/aesa/85.2.164

Piu G, Ceccio S, Garau MG, Melis S, Palomba A, Pautasso M, Pittau F, Ballero M (1992) Itchy dermatitis from Gynaikothrips ficorum March in a family group. Allergy 47(4): 441–442. doi: 10.1111/j.1398-9995.1992.tb02087.x

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*Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

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Friday Fellow: Brown spot of maize

by Piter Kehoma Boll

I’ll continue the parasite trend from last week, but this time shifting from human parasite to maize parasite, and from a prokaryotic to a eukaryotic parasite. So let’s talk about Physoderma maydis, commonly known as the brown spot of maize or brown spot of corn.

The Brown spot of maize is a fungus of the division Blastocladiomycota that infects corn (or maize) plants. Its common name comes from the fact that it causes a series of brown spots on the leaves of an infected plant.

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The brown spots seen on this corn leaf are due to an infection by Physoderma maydis. Credits of the photo to Clemson University – USDA Cooperative Extension Slide Series.*

The life cycle of the brown spot of maize is as complex as that of many fungi. The infection of the plants occur through spores that remain in the soil during winter and are carried to the host by the wind, germinating in the rainy season. The germinated spores produce zoospores, flagellated spores able to swim. Swiming through the maize leaf, the zoospores infect single cells and produce zoosporangia at the surface of the leaf. The zoosporangia release new zoospores that infect new cells. In late spring and summer, the zoospores produce a thallus growing deep inside the maize leaf that infects many cells and produces thick-walled sporangia. After the plants dies and the leaves become dry and broke, the sporangia are released and reach the soil, where they wait for the next spring to restart the cycle.

The brown spot of maize is a considerable problem for maize crops in countries with abundant rainfall. Heavy infections may kill the maize plant or severely reduce its fitness before the ears are ready to be harvested. Although fungicides may help in slowing down the infectio throughout the crops, one of the most efficient ways to reduce the damage is to destroy, usually by fire, the remains of the last harvest.

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References:

Olson, L. W.; Lange, L. (1978) The meiospore of Physoderma maydis. The causal agent of Physoderma disease of maize. Protoplasma 97: 275–290. https://dx.doi.org/10.1007/BF01276699

Plantwise Knowledge Bank. Brown spot of corn (Physoderma maydis). Available at: < http://www.plantwise.org/KnowledgeBank/Datasheet.aspx?dsid=40770&gt;. Access on Agust 7, 2017.

Robertson, A. E. (2015) Physoderma brown spot and stalk rot. Integrated Crop Management News: 679. http://lib.dr.iastate.edu/cropnews/679/

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Friday Fellow: Black Bread Mold

by Piter Kehoma Boll

Today’s Friday Fellow lives in our houses and our gardens, among our food and our crops. And every time we notice it, we get upset, because it means that something we were supposed to eat is now spoiled. Its name is Rhizopus stolonifer, or black bread mold.

rhizopus_stolonifer

The black bread mold growing on a peach. Photo by University of Georgia Plant Pathology Archive.*

Having a worldwide distribution, the black bread mold is mainly saprotrophic, growing on decaying fruits and bread. During its reproductive phase, it can be noticed as a black and hairy mold, as in the photo above. Eventually, this species can also cause an infection in human face and oropharynx, but most commonly it can be a pathogen of many plant species, thus being of economic concern.

rhizopus_stolonifer2

A closer look at the sporangia of Rhizopus stolonifer. Photo by Stanislav Krejčík.*

The black bread mold is a fungus of the order Mucorales, known as pin molds because their sporangia (the structures that contain the asexual spores) remember a pin. These sporangia, which are black, are what one usually notice growing on decaying food. When the sporangia are mature, they release spores of two kinds that germinate and originate two kinds of hyphae (known as + and -) and when two hyphae of opposite type come into contact, they fuse and create a zygospore, which then grows to originate new sporangia.

Due to its importance as an economic pest, there are many studies trying to find ways to get rid of it and very few studies trying to understand the fascinating things that it hides. What a pity.

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ResearchBlogging.orgReferences:

EOL – Encyclopedia of Life: Rhizopus stolonifer. Available at <http://eol.org/pages/2944808/overview >. Access on January 14, 2107.

Hernández-Lauzardo, A., Bautista-Baños, S., Velázquez-del Valle, M., Méndez-Montealvo, M., Sánchez-Rivera, M., & Bello-Pérez, L. (2008). Antifungal effects of chitosan with different molecular weights on in vitro development of Rhizopus stolonifer (Ehrenb.:Fr.) Vuill Carbohydrate Polymers, 73 (4), 541-547 DOI: 10.1016/j.carbpol.2007.12.020

Wikipedia. Black bread mold. Available at <https://en.wikipedia.org/wiki/Black_bread_mold >. Access on January 14, 2017.

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Friday Fellow: Pea Aphid

by Piter Kehoma Boll

Last time ago we presented a model organism, the red flour beetle, and this week I’m introducing one more. Its name is Acyrthosiphon pisum, commonly known as pea aphid or sometimes pea louse or green dolphin.

An adult pea aphid and two nymphs. Photo by Shipher Wu.*

An adult pea aphid and two nymphs. Photo by Shipher Wu.*

As it is usual with model organisms, the pea aphid has been deeply studied and therefore many curious things have been studied and discovered on it. A typical aphid, it feeds on plant sap, especially from legumes (family Fabaceae), including many forage crops, such as the pea, hence the name. As a result, it is a major agricultural pest worldwide.

The life cycle of pea aphids is quite unusual, although not so different from most aphids. Most of the population is composed by parthenogenetic females, i.e., females that reproduce by producing offspring without sex. These parthenogenetic females give birth to live nymphs, not laying eggs, so they are usually called viviparous parthogenetic females. During autumn, the lengthening of the night triggers the production of a single generation of sexual individuals, both male and females, by the parthenogenetic females. Males and sexual females then mate and the females lay fertilized eggs from which new parthenogenetic females will emerge.

Pea aphids are usually wingless, but when food become scarce they may produce winged individuals that fly to new food sources and colonize a new plant host. Such a complex life cycle makes them good models for the study of reproduction.

Another area in which the pea aphid is a good model is the study of symbiosis with bacteria. The bacteria Buchnera aphidicola is known to live in the aphid’s hemocoel (the body cavity in which hemolymph, insect “blood”, is found) and provides it with many essential aminoacids. Several other bacteria may be found living inside the aphid and they are able to have a profound influence in the insect’s physiology.

The pea aphid is one of the few animals known to be able to produce carotenoids, organic pigments usually produced by bacteria and plants (actually their chloroplasts, which are actually endosymbiotic bacteria). This ability may have been obtained by transference of bacterial genes to the aphid’s genome. Some time ago, it has been shown that pea aphids may use this carotenoids to produce ATP (energy-storing molecules) from sun light, a process similar to some kind of very primitive precursor of photosynthesis. It cannot be considered actual photosynthesis because there is no production (synthesis) of organic molecules using carbon dioxide.

Anyway, the pea aphid is nevertheless an astonishing little creature.

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References:

Chen, D.-Q.; Montlor, C. B. 2000. Fitness effects of two facultative endosymbiotic bacteria on the pea aphid, Acyrthosiphon pisum, and the blue alfafa aphid, A. kondoi. Entomologia Experimentalis et Applicata, 95 (3): 315-323.

Valmalette, J. C.; Dombrovsky, A.; Brat, P.; Mertz, C.; Capovilla, M.; Robichon, A. 2012. Light-induced electon transfer and ATP synthesis in a carotene synthesizing insect. Scientific Reports, 2: 579.

Wikipedia. Acyrthosiphon pisum. Available at: < https://en.wikipedia.org/wiki/Acyrthosiphon_pisum >. Access on June 10, 2015.

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