Leslie R. Campbell

Thrips as vectors of tospoviruses

Publisher Summary This chapter reviews the thrips– tospovirus pathosystem and the cellular and molecular determinants of thrips acquisition of tospoviruses. Viruses in the genus Tospovirus (family Bunyaviridae) are transmitted by thrips and have become an ever increasing problem for the producers of agricultural and horticultural crops worldwide. The genus Tospovirus is the genus within the Bunyaviridae containing plant-infecting viruses. Tomato spotted wilt virus ( TSWV) is the type species of this genus. Thrips cause significant direct damage to plants, but it is their transmission of tospoviruses that is most difficult to control and frequently causes the most severe damage to crops. At least ten species of thrips transmit tospoviruses, all of which are in the Thysanopteran family Thripidae. Most thrips vector species deposit their eggs into plant tissue and the eggs hatch after 2–3 days, depending on temperature and plant host. For tospoviruses to be transmitted by thrips, they must be acquired by the larvae. Thus, only immature thrips that acquire tospoviruses or adults arising from such immatures are important to the transmission of the virus. This concept is extremely important in managing tospoviruses, because only the plants that serve as hosts for both the insect and the virus are important in epidemics.

Feeding Behavior by the Soybean Aphid (Hemiptera: Aphididae) on Resistant and Susceptible Soybean Genotypes

Abstract The soybean aphid,Aphis glycines Matsumura (Hemiptera: Aphididae), is a major pest of soybean,Glycine max (L.) Merr. Since 2000, whenA.glycines was detected in the United States, several studies on this insect have been done in different areas, but there is no report of any studies of stylet penetration behavior byA.glycines on resistant and susceptible soybean. Assessment of feeding behavior of this aphid species was compared on four resistant entries (K1639, Pioneer® 95B97, Dowling, and Jackson) and a susceptible check (KS4202) by using the electrical penetration graph (EPG) technique. Feeding behavior ofA.glycines adults was recorded during a 9-h period. The average time needed to reach the first sieve element phase byA.glycines was 3.5 h in KS4202, whereas it was 7.5 h in the resistant entries. The total duration in the sieve element phase was longer than an hour in KS4202, and only 2 to 7 min in the resistant entries. These results suggest that morphological or chemical factors in the phloem tissue of resistant plants affect stylet penetration activities ofA.glycines. In the majority of the recordings, however, the aphid stylet reached the xylem phase before penetrating the sieve element, and the time that aphids spent ingesting xylem sap was not different among all entries. Therefore, it is possible that xylem sap in the resistant entries may contain toxic substances that change aphid behavior and that affect further activities in the sieve element phase.

Chlorophyll Loss Caused by Soybean Aphid (Hemiptera: Aphididae) Feeding on Soybean

Abstract The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a worldwide pest of soybean, Glycine max (L.) Merr. Studies to find control methods were initiated in 2000 when it was first detected in North America. A. glycines can reduce yields by as much as 50%, and it is the vector of several viral diseases. A. glycines removes phloem sap, which can result in a reduction of chlorophyll content. Quantification of chlorophyll loss caused by A. glycines feeding on soybean is of vital importance. The SPAD-502 chlorophyll meter is a device that has been used to measure chlorophyll loss caused by nonchewing insects. Chlorophyll loss was studied in no-choice tests on the infested and uninfested leaves of a susceptible check (KS4202). The minimum combined number of days and aphids needed to detect significant chlorophyll loss was 30 aphids confined for 10 d. In a similar experiment, seven resistant entries and two susceptible checks were evaluated. There was no significant chlorophyll reduction between infested and uninfested leaves of five of the resistant entries (K1621, K1639, Pioneer 95B97, Dowling, and Jackson). Percentage of loss of chlorophyll in the susceptible checks was ≈40%; Jackson and Dowling had a significantly lower percentage loss (13 and 16%, respectively) compared with the susceptible checks. The percentages of chlorophyll loss of K1621, K1639, and Pioneer 95B97 were not statistically different from the percentage of loss of Jackson. RESUMEN El áfido de la soya, Aphis glycines Matsumura (Hemiptera: Aphididae), es una plaga de la soya, Glycine max (L.) Merr. En el año 2000 SE encontró A. glycines en Norte América, y desde entonces, SE iniciaron estudios para encontrar métodos de control. Aphis glycines reduce el rendimiento en un 50%, y transmite virus. Aphis glycines extrae el floema de las hojas lo cual puede tener efectos en la fisiología de la soya como la reducción de clorofila. Por lo tanto, la evaluación de las pérdidas de clorofila en soya causadas por A. glycines es de mucha importancia. El medidor SPAD-502 SE usa para cuantificar pérdidas de clorofila causadas por insectos no masticadores. Se estudiaron las pérdidas en hojas infestadas y no-infestadas del testigo susceptible KS4202. Se descubrió que el número mínimo de áfidos necesario para observar pérdidas significativas de clorofila es de 30 áfidos confinados por 10 días. En un experimento análogo, siete genotipos resistentes y dos susceptibles fueron evaluados. De los genotipos resistentes, cinco (K1621, K1639, Pioneer 95B97, Dowling y Jackson) no mostraron reducción en su contenido de clorofila en hojas infestadas y no-infestadas. El porcentaje de pérdida de los genotipos susceptibles fue del 40% aproximadamente; Jackson y Dowling tuvieron porcentajes de perdida (13 y 16%, respectivamente) significativamente más bajos que los testigos susceptibles. Sin embargo, los porcentajes de K1621, K1639 y Pioneer 95B97 no fueron estadísticamente diferentes al porcentaje de pérdida de Jackson.

Electrical Penetration Graph Analysis of the Feeding Behavior of Soybean Aphids on Soybean Cultivars with Antibiosis

ABSTRACT The soybean aphid, Aphis glycine Matsumura (Hemiptera: Aphididae), is a major pest of soybean. In the current study, we used the Electrical Penetration Graph technique to study feeding behavior of soybean aphids on antibiotic-resistant soybean lines KS1621, KS1613, and KS1642, and a susceptible soybean line, KS4202. We observed that soybean aphids spent significantly shorter periods of time in the sieve element phase but slightly more times in nonprobing phases in all three resistant lines than in the susceptible control. Our study suggests that resistance factors exist in the phloem of the resistant soybean lines, and that these lines may contain antixenosis in addition to antibiosis.

Feeding behavior comparison of soybean aphid (Hemiptera: Aphididae) biotypes on different soybean genotypes.

ABSTRACT Soybean aphids have become a serious pest of soybean, Glycine max L. (Merrill), since they were first detected in North America in 2000. Three soybean aphid biotypes have been documented in the United States in the last 10 yr, but few studies have been done on their feeding behavior in the United States The Electrical Penetration Graph is a convenient and successful tool to study the feeding behavior of piercing and sucking insects. This is the first attempt to study the feeding behavior differences between biotype 1 and biotype 2 on soybean genotypes using the Electrical Penetration Graph technique, and includes both resistant and susceptible soybean genotypes from Kansas and Michigan. The experiments were run for 9 h each for each genotype with a total of eight channels at a time. Results indicated that aphids feeding on susceptible genotypes had a significantly greater duration of sieve element phase than when feeding on resistant genotypes. Furthermore, the time taken to reach the first sieve element phase in resistant genotypes was significantly greater than in susceptible genotypes. Most of the aphids reached sieve element phase (>90%) in susceptible genotypes, but only a few (<30%) reached sieve element phase in resistant genotypes during the 9-h recording period; however, we found no differences in any other probing phases between resistant and susceptible genotypes except the number of potential drops in biotype 2. Thus, the resistance was largely associated with phloem tissues. Therefore, some biochemical, physical, or morphological factors could affect stylet penetration of aphids.