Lixin Mao

Formosan Subterranean Termite (Isoptera: Rhinotermitidae) Soldiers Regulate Juvenile Hormone Levels and Caste Differentiation in Workers

Abstract A caste structure is maintained in termite societies and juvenile hormone (JH) is generally regarded as the most important regulator in these termite colonies. Here, we demonstrate that the soldier caste regulates JH in workers of Coptotermes formosanus Shiraki. Worker termites (80–100 individuals) were placed in petri dishes with 0, 5, 10, or 20% soldiers. JH III titers of groups of these workers were monitored at 14, 28, 42, and 56 d. Any changes in soldier caste proportions also were noted at each sample date. On the first sample date, the JH levels in workers were similar among treatments with different initial soldier proportions, and no new soldiers were formed. Over the next three sample dates, the worker JH levels were higher for low initial soldier proportion treatments and vice versa. Concurrently, soldier formation increased with lower initial soldier proportions. JH titers in workers showed a positive and statistically significant relationship to soldier numbers until a certain soldier proportion was reached. These results provide evidence that soldier caste proportions regulate JH levels and thereby caste differentiation in workers. The means by which this regulatory mechanism may proceed is discussed.

Antifeedant activity and acute and residual toxicity of alkaloids from Sophora flavescens (leguminosae) against formosan subterranean termites (Isoptera: Rhinotermitidae).

Abstract Ku Shen,Sophora flavescens Aiton (Leguminosae), contains alkaloids that possess broad biological activities. This study showed that total matrines (a mixture of the alkaloids), and matrine and oxymatrine (two major alkaloids) had a strong antifeedant effect against Formosan subterranean termite,Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), at all tested concentrations (ranging from 0.01 to 5%). Total matrines and matrine also had significantly toxic effects at 5%. The estimated LD50 of total matrines and matrine was 12.3 and 8.6 μg per insect, respectively, after 24 h; 13.3 and 7.1 μg per insect after 48 h; and 10.1 and 4.8 μg per insect after 1 wk. The antifeedant and toxic properties of total matrines- and matrine-treated wood remained effective at least 12 mo after treatment under both light and dark storage conditions. These chemicals have great potential for commercial development as wood treatment agents.

Toxicity of seven termiticides on the formosan and eastern subterranean termites.

ABSTRACT Using both topical application and substrate (sand) treatments the toxicities of seven new generation soil termiticides were evaluated to determine the LD50 and LC50 against two economically important subterranean termite species, eastern subterranean termite, Reticulitermes flavipes (Kollar), and Formosan subterranean termite, Coptotermes formosanus Shiraki. The lethal dose toxicity (LD50) rankings for R. flavipes from highest to lowest were: fipronil > bifenthrin > chlorantraniliprole > cyantraniliprole > imidacloprid > chlorfenapyr > indoxacarb; the rankings for C. formosanus were fipronil > imidacloprid > chlorantraniliprole > cyanthraniliprole> bifenthrin > chlorfenapyr > indoxacarb. The respective lethal concentration toxicity (LC50) rankings were fipronil > bifenthrin > chlorfenapyr > indoxacarb > cyantraniliprole > chlorantraniliprole > imidacloprid for R. flavipes; and fipronil > chlorfenapyr > bifenthrin > imidacloprid > cyantraniliprole > chlorantraniliprole > indoxacarb for C. formosanus. The study provides an opportunity to directly compare toxicity, action speed, and bioavailability among this group of newer generation soil termiticides.

Seasonal Variation of Juvenile Hormone Titers of the Formosan Subterranean Termite, Coptotermes formosanus (Rhinotermitidae)

Abstract In lower termites, the soldier is the only sterile caste. Through hormonal control, soldiers seem to promote caste differentiation of workers to the reproductive caste. However, little data exist on how hormonal levels change in soldiers and workers in the field and how this may tie into the seasonal reproductive formation. Our objective was to collect baseline data on hormonal changes in colonies of subterranean termites in the field. Over a 1-yr period, the seasonal variation of juvenile hormone III (JH) titers was determined for Coptotermes formosanus Shiraki soldiers and workers collected monthly from field colonies infesting isolated cypress trees (Taxodium distichum L. Rich.). A total of five colonies were evaluated. Soldier JH titers leveled from February through May, with peak values in June and July. JH titers in workers followed a similar trend. Both soldier and worker JH titers remained at low levels in the fall and winter. This is the first effort to correlate physiological and hormonal aspects with soldier production in the field. Seasonal changes in JH titers as an intrinsic mechanism for reproductive caste differentiation is also discussed.

Effects of Temperature and Nutrition on Juvenile Hormone Titers of Coptotermes formosanus (Isoptera: Rhinotermitidae)

Abstract Colony organization via caste specialization in the Formosan subterranean termite, Coptotermes formosanus Shiraki, as in other species of termites, seems to be influenced by external factors such as nutrition and temperature. Here, we report on the influence of nutrition and temperature and the associated juvenile hormone levels on the regulation of the soldier caste. Two nutritional levels of food sources or five different temperatures were provided to C. formosanus workers in the laboratory. Juvenile hormone titers of these workers were monitored on 0, 12, 24, 36, 48, and 60 d after treatment. Termite survival and soldier-to-worker proportions also were recorded at each sample date. Workers fed a high-quality food source produced significantly more soldiers and this was associated with high worker juvenile hormone (JH) titers. JH titers in workers maintained at 20 and 36°C remained constant throughout the observational period with no presoldier or soldier formation. Under 24, 28, and 32°C temperature regimes, JH titers in workers climbed to a peak at day 48 and then sharply dropped at day 60 when soldier proportion increased to a specific value. At each sample date, JH titers in workers demonstrated a positive and statistically significant relationship to temperatures within the range of 24–32°C, but upon inclusion of temperatures below 24 and above 32°C, the correlation is no longer significant. The results show that favorable extrinsic conditions of temperature and nutrition allow for a higher soldier proportion threshold through the regulation of JH levels and caste differentiation in workers.

Germination of Various Weed Species in Response to Vetiver Oil and Nootkatone

Germination experiments were conducted in petri dishes to test the effect of vetiver oil and one of its minor components, nootkatone, on six common weed species. Vetiver oil inhibited germination of redroot pigweed, common lambsquarters, giant ragweed, pitted morningglory, and velvetleaf. Nootkatone, at much higher concentrations than it occurs in the oil, exhibited germination inhibition for all weed species except velvetleaf. Redroot pigweed was the most sensitive species with germination inhibition at 0.1 to 1.0 mg/ml of vetiver oil and nootkatone. At 1.0 to 8.0 mg/ml, nootkatone reduced germination of giant ragweed by 24 to 92%, whereas vetiver oil reduced the germination only by 6 to 11%. Vetiver oil and nootkatone also inhibited seedling expansion of redroot pigweed and common lambsquarters. No significant inhibition of germination and seedling expansion was found for sicklepod. These laboratory studies provide preliminary evidence that nootkatone and vetiver oil may have use as herbicides. Nomenclature: Nootkatone, 5,6 dimethyl-8-isopropenylbicyclo[4.4.0]dec-1-en-3-one; common lambsquarters, Chenopodium album L. #3 CHEAL; giant ragweed, Ambrosia trifida L. # AMBTR; pitted morningglory, Ipomoea lacunosa L. # IPOLA; redroot pigweed, Amaranthus retroflexus L. # AMARE; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby # CASOB; velvetleaf, Abutilon theophrasti Medicus # ABUTH. Additional index words: Amaranthus retroflexus, Ambrosia trifida, Chenopodium album, essential oil, herbicidal activity, sesquiterpene. Abbreviations: I50, concentration required to inhibit 50% of seed germination.

Group size effect on worker juvenile hormone titers and soldier differentiation in Formosan subterranean termite.

In a finite environment, population growth can lead to crowding, increased densities and stress. Termites live in highly organized societies and densities can increase astronomically as colonies grow. However, little is known about juvenile hormone (JH) changes in these insects as numbers increase, despite the fact that JH is a critical caste regulator in this insect. Using Formosan subterranean termites as a model, we evaluated minimum group size requirements for soldier differentiation and the effect of density (50, 100, 500, and 1000 individuals/experimental unit) on worker JH titers either with or without initial soldiers being present. The minimum group size investigation indicated that groups initiated with 5 workers were insufficient for soldier differentiation. Soldiers were produced in groups initiated with 10 or more workers. As density increased from 50 to 1000 individuals per experimental unit, worker JH levels were elevated. Presence of soldiers lessened the effect of density on rising worker JH titers, indicating that soldiers have the ability to down-regulate worker JH. The study provides direct evidence of a population density effect on JH in eusocial insects and sheds light on understanding of the regulatory mechanisms associated with termite soldier caste differentiation.

Liquid chromatography-electrospray ionization-mass spectrometric quantitation of juvenile hormone III in whole body extracts of the Formosan subterranean termite.

Juvenile hormone (JH) III is responsible for control of a variety of insect physiological and developmental states, including caste differentiation of the Formosan subterranean termite (Coptotermes formosanus Shiraki). We report here a simplified, efficient sample preparation and an optimized LC-ESI-MS method for quantifying JH III in whole body extracts. Sample preparation comprises hexane extraction (from termite whole bodies) and C18 cartridge purification. Previous LC-ESI-MS protocols exhibited the following two problems: (1) ion fragmentation differed when comparing spectra from insect samples and authentic JH III and (2) a JH III monitoring ion was not resolved from other unknown compounds in whole body samples from termites. To overcome these problems, we used a pentafluorophenyl LC column and water/acetonitrile containing ammonium acetate as solvent. In a mass chromatogram (m/z 235) of termite samples, a peak was detected at the retention time of authentic JH III, and MS(2) of this peak confirmed that the ion is a fragment of JH III, [M-CH(3)OH+H](+), being the base peak in both termites and authentic JH III samples. The protocol enables quantification of JH III in a single termite with signal/noise >10:1 and the limit of quantification is 21pg.

Physical contact between soldier and worker is essential in soldier self-regulation of Coptotermes formosanus (Isoptera, Rhinotermitidae)

Abstract.In a termite society, the soldier proportion is regulated at a species-specific level with a seasonal fluctuation. A feedback mechanism in soldier proportion regulation is well recognized, while the proximate means by which the presence of soldiers inhibits the new soldier formation from workers remains mostly elusive. In the present study, some possible means for this inhibition were tested with the Formosan subterranean termite, Coptotermes formosanus Shiraki. The results showed that neither soldier-originated volatiles nor non-volatile chemicals without physical contact were responsible for the inhibition of new soldier formation. The essentiality of physical contact between workers and soldiers in soldier regulation was established. However, by physical contacts, as the soldier-replacement experiment showed, workers could not individually recognize or “count” soldiers to maintain a set soldier proportion. The possible feedback mechanisms for soldier regulation are discussed.

Application of ground penetrating radar in detecting the hazards and risks of termites and ants in soil levees.

ABSTRACT A ground penetrating radar (GPR) technique was used to detect Formosan subterranean termite (Coptotermes formosanus) and red imported fire ant (Solenopsis invicta) hazards and risks (targets) in a soil levee at the London Avenue Canal in New Orleans, LA. To make this assessment, GPR signal scans were examined for features produced by termite or ant activities and potential sources of food and shelter such as nests, tree roots, and voids (tunnels). The total scanned length of the soil levee was 4,125 m. The average velocity and effective depth of the radar penetration was 0.080 m/ns and 0.61 m, respectively. Four hundred twenty-seven targets were identified. Tree roots (38), voids (31), fire ant nests (209), and metal objects (149) were detected, but no Formosan termite carton nests were identified. The lack of identified termite nests may be related to drowning events at the time to the flood. Based on the target density (TD), the two new floodwall and levee sections that were rebuilt or reinforced after they were destroyed by Hurricane Katrina in 2005 were determined to be at low potential risk from termites and ants. A merging target density (MTD) method indicated a high potential risk near one of the breached sections still remains. Foraging and nesting activity of Formosan subterranean termites and red imported fire ants may be a contributory factor to the levee failure at the London Avenue Canal.