Abstract. A 3-yr study was conducted in California’s southern San Joaquin Valley to determine the overwintering survival of the corn leafhopper, Dalbulus maidis. The corn leafhopper, Dalbulus maidis (Delong and Wolcott) is found only in subtropical and tropical areas of America. Its host range is limited to maize and its . The corn leafhopper, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae), is one of the most important pests of corn, Zea mays L. (Poaceae), in Latin.
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Cicadellidaeand Spiroplasma kunkelii Mycoplasmatales: Corn leafhopper populations were sampled from November to March using yellow sticky cards, D-vac suction samples, and inspection of volunteer corn plants and spring planted corn. Leafhoppers were collected on yellow sticky cards throughout the winter during all 3 yr.
They were also regularly recovered from alfalfa, Medicago sativa L. Volunteer plants were determined to be a critical key in leafhopper overwintering, and consequently, the survival of S.
Volunteers extended the season by as much as 2 mo, thus shortening the period of time the leafhoppers were forced to go without a food source. The possible reasons for a shift in the leafhopper from cyclic pest to persistent pest in the region are also discussed.
In addition to yield losses caused by feeding injury Bushing and Burtoncorn leafhopper is a vector of corn stunt spiroplasma CSSSpiroplasma kunkelii Whitcomb et al.
Corn stunt disease can result in even more significant yield losses than those attributable to direct leafhopper feeding NaultMoya-Raygoza and Nault Currently in California, of the three entities, only S. Although plants with MBSP-like symptoms have been observed, recent attempts to recover this pathogen have been unsuccessful C. The corn leafhopper was first reported causing injury to field corn in Fresno and Tulare counties in Frazier Since that outbreak, corn leafhopper was not reported again until the late s Bushing and BurtonBushing et al.
Apparently, damage was due solely to leafhopper feeding, because no evidence of corn stunt disease was reported. Corn leafhopper reappeared inand corn stunt was apparently present in at least some fields Kloepper et al. The report by Kloepper et al.
Incorn leafhopper populations reached extremely high levels on late-maturing field corn silage and grain and sweet corn in Fresno, Tulare, and Kings counties C. In addition, many fields had a high incidence of corn stunt disease, and S.
The combination of leafhopper feeding and disease resulted in substantial yield and quality losses. Since then, the presence of leafhopper populations mqidis the incidence of corn stunt disease have continued yearly in the southern San Joaquin Valley SJV. Ability of the corn leafhopper to overwinter in California has been the subject of considerable speculation. Corn and teosinte, Zea spp. Teosintes do not occur in California, and corn does not usually survive throughout the winter here.
Because there are no overwintering hosts for D. In other areas of the United States, investigators have speculated that infestations came from elsewhere as well. Nault noted that the appearance of D.
In California, before the outbreak, leafhoppers appeared only late in the ,aidis August and Septemberthus giving credence to the theory that they maidus northward from Mexico, arriving late in the growing season.
Corn leafhopper overwintering biology was never investigated. After the leafhopper outbreaks, D. This observation suggested to us that the leafhopper was overwintering in the area rather than migrating here from Mexico. Natwick, personal communicationdespite that county’s large acreage of sweet corn, which is just across the border from Mexico. It would seem reasonable that leafhoppers migrating north from Mexico would infest corn planted in its path as it progressed northward. This paper reports the results of studies conducted to determine the overwintering capabilities of D.
Double-sided yellow sticky cards, 7. Beginning in October or November, the sticky cards were placed adjacent to corn fields in Fresno, Kings, and Tulare Counties that had high numbers of corn leafhopper during the previous summer, next to alfalfa fields, and in riparian areas next to fields previously planted to corn. The traps were replaced weekly or biweekly, depending on weather conditions.
Traps were returned to the laboratory, and the number and sex of leafhoppers on each card was determined. Areas adjacent to heavily infested corn fields were sampled beginning in October or November using a D-vac suction machine Rincon-Vitova, Ventura, CA with a 0. Areas suspected of harboring leafhoppers, including weedy fields, ditch and fence lines, alfalfa Medicago sativa L.
maize leafhopper (Dalbulus maidis)
During the winter of andvolunteer plants were examined during January, February, and March for the presence of surviving leafhoppers. Plants were cut at ground level, transported to the laboratory where they were chilled to slow leafhopper movement, and examined for the presence of adults and nymphs. Both plantings were adjacent to a corn field that had high populations of corn leafhopper the previous fall. Plants containing leafhoppers were marked with surveyor’s flags dapbulus tested 6 wk later for the presence of S.
Commercially planted corn in grower fields was also examined for the presence of leafhoppers and tested for the occurrence of the spiroplasma. Sentinel corn plants ‘Asgrow RX’ were grown in an insect free greenhouse in cm pots, three plants per pot.
Plants were watered as necessary. At the end of 2 wk, plants were transported to the laboratory and placed in the greenhouse, and new potted corn plants were placed in the field. The presence of S. When testing immature corn, a portion of the mid-rib, found to contain a high titer of spiroplasma, was removed from symptomatic leaves. A portion of the tassel rachis was used in mature plants.
The tissue was macerated on a laboratory bench using a large-faced brass mallet, a small amount of general extract buffer, pH 7. Antibodies were made in rabbits using a CSS corn stunt spiroplasma -purified antigen and a standard alkaline phosphatase conjugate enzyme system. Plates were coated overnight, and samples were prepared and applied the next maiis.
Substrate was added at room temperature under moist conditions and incubated for min depending on the rapidity of response. The plate wells were initially scored visually as they developed, and later, after fixing, the enzyme reaction was read with a plate reader E-max ; Molecular Devices, Sunnyvale, Maifis at nm.
Positives were at least 2. Dakbulus captured on the sticky cards and those collected in D-vac samples were examined for the presence of S. The amounts of reagents used dakbulus the preparation were determined by the number of leafhoppers in the sample. Primers used for the specific identification of S. As few maidia two adult leafhoppers were able to produce a Mairis positive, but in most cases, samples from which DNA was extracted contained five insects.
The PCR products were run on a 1. In the early season, the PCR product of the reaction was used in a second reaction, and distinct bands were observed. In two separate situations, suspected S. Adult leafhoppers were captured on yellow sticky cards throughout the winter in all 3 yr Fig.
Duringadults were captured each month Fig. Incaptures on yellow sticky cards were less frequent Fig. The gaps in collections represent periods of particularly cold weather, when temperatures were below the flight threshold. The sites denoted as Dover, Dairy, 18th East, and Eighth Kings County all represent locations adjacent to corn dalbuljs, whereas the River site was a riparian area in Kings County, consisting maidiw of grassy weeds located along the Kings River.
Crop rotations required new trapping locations in Fig. The zeros in trap catches from December to February corresponded with cold weather and problems in maintaining the trap line because of localized flooding. However, collections beginning in early March were similar to those of previous years. Those collections 11 March occurred before spring planted corn emerged. Leafhoppers trapped after 20 March of all 3 yr dalbulks with newly planted corn.
D-vac suctions proved a reliable technique for recovering leafhoppers. Adults were consistently collected from both alfalfa and weedy areas throughout the winter Fig. As spring approached, we began dalbulsu routinely collect leafhoppers from winter forage. As with the sticky card dablulus, collections using the D-vac overlapped in time with the spring planted corn crop, again indicating that the adults had survived the period between the last corn in the fall and newly planted corn in the spring.
Females surviving the winter outnumber males by a wide margin Table 1. There was a general trend for an increased percentage of males surviving the winter over the 3 yr. Percentage of overwintering a male and female D. Although the outer leaves dalbklus the volunteer corn plants froze, the whorl leaves remained viable throughout the winter and supported populations of both adult and immature leafhoppers Fig.
Both stages were found throughout the winter into March, when leafhopper populations from volunteer plants Fig. Even though the corn was completely frozen by late November, leafhopper adults and nymphs continue to survive within the frozen plants until well into February Fig. Nymphs failed to survive the entire winter of midis were not recovered in March when new corn was being planted.
Adults continued to survive the entire winter as determined by the D-vac samples. The mild winter of resulted in the survival of large numbers of volunteer corn plants throughout the entire winter.
These volunteers can serve as an early host for leafhoppers who become infective after feeding. In both years, corn planted adjoining a corn field that had dalgulus leafhopper population the previous season was colonized almost immediately after seedling emergence.
Based on maidls separate observations, 20 and 16 adult leafhoppers were found in andrespectively.
Based on these numbers, we calculated an average of 1, and 1, adult leafhoppers per hectare in andrespectively. In4 of 35 plants observed to contain an adult leafhopper were positive for the presence of S. Sentinel plants, placed in the field to detect the presence of S. Infected plants were found among the sentinel plants placed in the field in January through April.
Infected leafhoppers were recovered throughout the winter and spring in all 3 yr. These leafhoppers came from several locations throughout Kings, Tulare, and Fresno counties Table 2. Infected leafhoppers recovered in March were capable of transmitting the spiroplasma to newly planted corn, which overlapped with the time frame in which the infected leafhoppers were recovered. From the s to the s, serious outbreaks of D. Previous field studies on the leafhopper in California were restricted to chemical control evaluations on late season corn Bushing and BurtonBushing et al.
Until this study, nothing was known regarding the overwintering of either the leafhopper or the spiroplasma.