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Project description

Threshold temperature and thermal time requirement for life cycle of the sting nematode. (01XU027)
Program Exotic Pests and Diseases Research Program
Principal
investigator 		J.O. Becker, Nematology, UC Riverside
Host/habitat Turfgrass
Pest Sting Nematode Belonolaimus longicaudatus
Discipline Nematology
Review
panel 		Urban Systems
 Start year (duration)  2001 (Two Years)
Objectives Determine temperature-dependant duration of embryonic development of the sting nematode in gnotobiotic culture.

Determine thermal time requirement and heat sum for the complete development cycle of the sting nematode in gnotobiotic culture.

Confirm and support data collected under b) with thermal time studies on sting nematode development in environmental growth chambers.

Final Report The sting nematode is one of the most devastating phytonematode pests in this country. It is native to the southeastern US but was detected a decade ago in various golf courses in California's Coachella Valley. Many of the biological and ecological aspects of the sting nematode's life are still unknown. Initially, we monitored the effect of temperature on the development of B. longicaudatus by microscopic observations of the nematodes on root culture plates. In addition, greenhouse-cultivated ryegrass cultures were infested with B. longicaudatus and destructively sampled to confirm the in vitro results. Embryogenesis was completed in 3 to 11 days at constant temperatures between 20 and 32ūC. Minimum threshold temperature for embryogenic development was determined to be 13.1ūC. The thermal-time requirement for completion of embryogenesis was 64.3 degree-days. As with the embryogenic development, completion of the life cycle of B. longicaudatus was linearly related to the temperature between 20 and 28 ūC. Minimum threshold temperature for the development of the sting nematode was 12. ūC. Completion of the life cycle was achieved after 365 degree days. In vitro trials with sting nematode-infested ryegrass cultures confirmed the thermal time requirements obtained with the in vitro cultures. The observed and predicted values of thermal time and the minimum duration for different temperature did not differ significantly.

Second-year
progress 		The sting nematode, Belonolaimus longicaudatus was detected in the Coachella Valley, CA in the beginning of the 1990. Despite its currently limited distribution, it is considered as an established invasive species for this state. Our goal was to gather information concerning biological and ecological aspects of the nematode that are essential to devise rational strategies for its management and containment. The effect of temperature on development of B. longicaudatus was monitored on excised root culture plates. In addition, growth chamber pot cultures with B. longicaudatus on ryegrass were used to verify the in vitro results. The minimum days and thermal time requirement for development from J2 to the genital primordium, fourth molt, adult, and second stage juvenile of the next generation were recorded separately. Rate of development of B. longicaudatus were linearly related to temperature between 20 and 28 ūC. On a thermal time basis, the threshold temperature for the development of B. longicaudatus was determined to be 12.8 ūC and the completion of the life cycle took 365 degree days. Freshly hatched J2 of the second generation were first collected at 52, 36, 29, 24, and 45 days after inoculation of J2 at temperatures of 20, 24, 26, 28, and 30 ūC, respectively. The observed and predicted values of thermal time and the minimum duration for different temperature did not differ significantly (P=0.01). Growth chamber trials with sting nematode infested ryegrass cultures confirmed the thermal time requirements observed with the in vitro cultures.

First-year
progress 		Many plant-pathogenic nematodes species in California were originally exotic species. The sting nematode is a fairly recent introduction and is still limited in distribution. Our sting nematode study is therefore a model for other possible introductions. The objective of our study is to fill the gaps of information concerning the basic biology and ecology of the sting nematode and use this information to devise rational strategies for exotic nematode management and containment. Embryogensis of Belonolaimus longicaudatus was monitored on water agar plates at six temperatures between 20 and 32 C. B. longicaudatus completed its embryogenic development in 3 to 11 days. At temperatures from 28 to 32 C, embryogenesis was nearly 1-1/2 to 2 times as rapid as at 24 C and 26 C, respectively, and about 3 times faster than at 20 C. Initial cleavage occurred within one to two hours at each temperature tested. The development to the blastula and gastrula stage required at least two days and four days, respectively, at 20 C, whereas the gastrula stage was reached within 2 days at temperatures above 28 C. First-stage juveniles were fully developed after two to seven days. The first molt to second-stage juveniles was initiated in the egg and was completed at hatching. The rate of development increased linearly between 20 C and 30 C. The lower threshold temperature for development was estimated by reverse extrapolation to be 13.1 C. The thermal-time requirement for development above this threshold was approximately 64.3 degree-days.

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