The clock gene Cryptochrome 1 is involved in the photoresponse of embryonic hatching behavior in Bombyx mori

The hatching of insect eggs is a classic circadian behavior rhythm controlled by the biological clock. Its function is considered to impose a daily rhythm on the embryo, allowing it to hatch within a permissible time window. However, the molecular pathways through which the clock affects embryonic hatching behavior remain unclear. Here, we utilized a clock gene Cryptochrome1 (Cry1) knockout mutant to dissect the pathways by which the circadian clock affects embryonic hatching rhythm in the silkworm. In the Cry1 mutant, the embryo hatching rhythm was disrupted. Under the constant light or constant dark incubation conditions, mutant embryos lost their hatching rhythm, while wild-type embryos hatch exhibiting free-running rhythm. In the light-dark cycle (LD), the hatching rhythm of CRY1-deficient silkworms could not be entrained by the LD photoperiod during the incubation period. The messenger RNA levels and enzymatic activities of Cht and Hel in the mutant embryos were significantly reduced at circadian time 24 (CT24). Transcriptome analysis revealed significant differences in gene expression at CT24 between the Cry1 knockout mutant and the wild-type, with 2616 differentially expressed genes identified. The enriched Gene Ontology pathway includes enzyme activity, energy availability, and protein translation. Short neuropeptide F signaling was reduced in the CT24 embryonic brain of the mutant, the expression of the neuropeptide PTTH was also reduced and the rhythm was lost, which further affects ecdysteroid signaling. Our results suggested that the silkworm circadian clock affects neuropeptide-hormone signaling as well as physiological functions related to hatching, which may regulate the hatching rhythm.

A Phenology Model for Asian Gypsy Moth Egg Hatch

Phenology models are useful tools in pest management interventions, biosecurity operations targeting alien invaders, and answering questions regarding the potential for range expansion/shift. The Gypsy Moth Life Stage model (GLS) has been used to predict the invasive range of the North American gypsy moth (Lymantria dispar dispar Linnaeus [Lepidoptera: Erebidae]) in North America and New Zealand. It has been used to examine the role of supra-optimal temperatures in range expansion/stasis/retraction. However, GLS has also been used where the target organism is the Asian subspecies L. d. asiatica Vnukovskij, despite observed differences between the predominant phenotypes of the two subspecies in the temperature requirements for egg hatch and the absence of egg phenology model parameters specific to the Asian phenotype. Here we describe the results of temperature and exposure duration on the timing of Asian gypsy moth egg hatch, and we present phenology model parameters for the Asian phenotype. Sum of squared differences (observed minus predicted day of median egg hatch) was reduced from 7,818 d2 (North American parameters) to 178 d2. Days of simulated median egg hatch differed from the observed days by 0-7 d (x¯=0.2; SD=3.1). The pattern of simulated egg hatch closely mimicked the irregular pattern of observed egg hatch from the temperature regimes of our experiment. Egg hatch is arguably the most important life cycle event in gypsy moth population suppression/eradication interventions and in estimating their potential invasive range. The model parameters described here produce accurate predictions of Asian gypsy moth egg hatch.

In vitro screening of 51 birdsfoot trefoil (Lotus corniculatus L.; Fabaceae) strains for anti-parasitic effects against Haemonchus contortus

Secondary plant compounds have shown bioactivity against multi-drug resistant Haemonchus contortus in small ruminants. This study screened 51 strains of birdsfoot trefoil (BFT, Lotus corniculatus) crude aqueous extracts (BFT-AqE) for anti-parasitic activity in vitro against egg hatching, and of those 51 strains, 13 were selected for further testing of motility of first (L1) and third stage (L3) larvae, and exsheathment of L3. Proanthocyanidin content ranged between 1.4 and 63.8 mg PAC g-1 powder across the 51 BFT strains. When tested against egg hatching, 21 of the 51 aqueous extracts had an EC50 of 1-2 mg powder mL-1, 70% of the strains were >90% efficacious at 6 mg powder mL-1 and 11 of the strains were 100% efficacious at 3 mg powder mL-1 BFT-AqE. Across the 13 strains tested against L3, efficacy ranged from 0 to 75% exsheathment inhibition, and 17 to 92% L3 motility inhibition at a concentration of 25 mg powder mL-1 BFT-AqE. There was no correlation between the PAC content of BFT powders and the anti-parasitic activity of aqueous extracts, therefore other secondary compounds may have contributed to the observed anti-parasitic effects. Further testing of BFT using bioactivity-driven fractionation and screening of BFT populations for the identified anti-parasitic compounds is needed.

Botanical Compound p-Anisaldehyde Repels Larval Lone Star Tick (Acari: Ixodidae), and Halts Reproduction by Gravid Adults

The lone star tick, Amblyomma americanum (L.), widely distributed across eastern, southeastern, and midwestern regions of the United States and south into Mexico, is an obligate blood feeder that attaches to three hosts during the larval, nymphal, and adult stages. White-tailed deer and wild turkey are common hosts, as well as a wide variety of other avian and mammalian hosts. Amblyomma americanum is the most frequently reported species of tick to bite humans in the southeastern and southcentral United States, and it can transmit diseases that include erhlichiosis, rickettsiosis, tularemia, and protozoan infections. As A. americanum resistance to conventional insecticides becomes more common, alternative control tactics, such as application of bioactive botanical natural products are being investigated. p-Anisaldehyde has been found in many plant species and it has shown effects that include mortality, attractancy, and interference with host seeking. The series of bioassays we developed was effective for assessing a range of ixodid tick responses to chemicals. This first assessment of p-anisaldehyde on ticks focused mostly on larvae, usually the most vulnerable free-living stage, and on egg production by adults. Contact exposure to larvae resulted in an LD50 of 0.162% and an LD90 of 0.311% p-anisaldehyde. Although fumigation was not lethal to larval A. americanum, p-anisaldehyde was strongly repellent against them in several bioassays that indicate aspects of the repellency such as counteracting the negative geotaxic orientation on a vertical surface, the ability to trap larvae between and inside treatment barriers on different substrates and to divert upward larval movement from one surface to another, and the extent to which larvae fall from a treated surface. The compound at a relatively low concentration applied to gravid adults strongly reduces egg laying and the few eggs that are produced do not hatch. Aside from repelling larval A. americanum and halting reproduction, p-anisaldehyde has a variety of effects on other arthropods including attraction. Research on this compound as a potentially multifaceted pest management tool has been sparse. This study, for example, is the first to demonstrate p-anisaldehyde's repellent properties against an arthropod pest. p-Anisaldehyde might also act as a strong repellent against other tick species.

Impact of temperature on postdiapause and diapause of the Asian gypsy moth, Lymantria dispar asiatica

Lymantria dispar asiatica (Vnukovskij) (Lepidoptera: Lymantridae) is one of three gypsy moth subspecies found in East Asia. Understanding the diapause and postdiapause phases of its eggs is important in characterizing its life cycle. The effects of different constant temperatures for different lengths of times on field-collected, postdiapause eggs were tested during the first year. In the second year, the effects of the same treatments on laboratory-raised eggs in diapause were investigated. The effects of temperature on percent egg hatching, time to hatching, and hatching duration were determined. When field-collected eggs were held at 0 and 5°C, they terminated postdiapause within 11 days. The percent hatching tended to decline with an increased duration of exposure at temperatures greater than 5°C. Diapause terminated slowly (> 37 days) and with a high percentage of hatching for postdiapause eggs held at 10°C. There was a positive correlation between temperature and the speed of postdiapause development for field-collected eggs held at constant temperatures between 10 and 25°C. However, the number of days to the first hatch was significantly longer than for eggs treated with lower temperatures before being transferred to 25°C. Freshly oviposited eggs treated at a constant 0 or 5°C for 200 days were unable to develop into pharate larva. However, eggs treated at a constant 20 or 25°C for 200 days developed into pharate larva but did not hatch even after a subsequent chill. This result suggests why L. dispar asiatica is not found in tropical areas and helps us to predict the distribution of the gypsy moth in China.

Comparison of Meldola's Blue Staining and Hatching Assay with Potato Root Diffusate for Assessment of Globodera sp. Egg Viability

Laboratory-based methods to test egg viability include staining with Meldola's Blue and/or juvenile (J2) hatching assays using potato root diffusate (PRD). These two methods have not been tested under identical conditions to directly compare their assessments of Globodera egg viability. Using two bioassay strategies, cysts from a Globodera sp. population found in Oregon were subjected to both viability assessment methods. In strategy one, intact cysts were first stained with Meldola's Blue (primary staining) and eggs were then transferred to PRD (secondary hatching). In the second strategy, intact cysts were exposed to PRD (primary hatching) and then unhatched eggs were transferred to Meldola's Blue (secondary staining). Two different cohorts of cysts were evaluated using these experimental strategies: cohort 1 was comprised of cysts produced on potato in the greenhouse that exhibited low hatch when exposed to PRD and cohort 2 consisted of field-collected cysts whose eggs yielded significant hatch when exposed to PRD. Percentage viability was calculated and is expressed as the number of hatched J2 or unstained eggs/total number of eggs within a cyst. With field-produced cysts, primary staining with Meldola's Blue and hatching with PRD produced similar viability estimates, with averages of 74.9% and 76.3%, respectively. In contrast, with greenhouse-produced cysts the two methods yielded much lower and unequal estimates 32.4% to 2.2%, respectively for primary hatching and staining methods. In addition, J2 hatch from unstained (viable) greenhouse-produced eggs was 13.7% after secondary exposure to PRD compared to 61.5% for field-produced eggs. The majority of eggs remaining unhatched after primary exposure to PRD (> 87%) stained with Meldola's Blue regardless of cyst cohort. Staining with Meldola's Blue provided a conservative assessment of egg viability compared to hatch assay with PRD regardless of diapause.

Effects of Heat Shock on Survival and Reproduction of Two Whitefly Species, Trialeurodes vaporariorum and Bemisia tabaci Biotype B

The effects of heat shock on survival and reproduction of two whitefly species, Trialeurodes vaporariorum (Westwood) and Bemisia tabaci (Gennadius) biotype B (Homoptera: Aleyrodidae), were compared in the laboratory. Whitefly adults were exposed to 26 (control), 37, 39, 41, 43 and 45°C for 1 hour, and were then maintained at 26°C. Adult survival was significantly affected when they were exposed at 41°C or higher for B. tabaci or 39°C or higher for T. vaporariorum. All males of T. vaporariorum were killed at 45°C. In both whitefly species, females were more tolerant to high temperatures at 39°C or higher than males. Female fecundity was not significantly different when B. tabaci adults were heat-shocked at all temperatures. In contrast, the fecundity of T. vaporariorum females declined with the increase of temperature, and only a few eggs were oviposited at 43°C. Survival or hatch rates of the F1 nymphs of both whitefly species declined as heat-shock temperature increased, and no T. vaporariorum nymphs were hatched at 43°C. Similarly, percentages of F1 offspring developing to adults for both whitefly species also declined as the heat-shock temperature increased. Sex ratios of the F1 offspring were not significantly affected for T. vaporariorum but were slightly affected for B. tabaci at 43 and 45°C. The significance of heat shock in relation to dispersal, distribution and population dynamics of the two whitefly species is discussed.

Heterodera glycines Cyst Components and Surface Disinfestants Affect H. glycines Hatching

We investigated the effects of Heterodera glycines cyst components and surface disinfestants on hatching of H. glycines eggs in vitro. Eggs were incubated in either H. glycines cyst wall fragments, cyst wall and egg rinsate, egg homogenate, or control solutions of soybean root diffusate, sterile distilled water, or zinc sulfate. Hatch in cyst wall and egg rinsate, and egg homogenate, was greater (alpha = 0.05) than hatch in sterile distilled water; however, it was not different from hatch in zinc sulfate according to Dunnett's test. Hatch in cyst wall fragments was similar to hatch in sterile distilled water. To determine whether surface disinfestants affected hatch, eggs were treated first with chlorhexidine diacetate, mercuric chloride, sodium hypochlorite, or streptomycin sulfate and then incubated in H. glycines egg homogenate, soybean root diffusate, sterile distilled water, or zinc sulfate. Hatch of eggs treated with chlorhexidine diacetate, mercuric chloride, and streptomycin sulfate was reduced (alpha = 0.05), and hatch of eggs treated with sodium hypochlorite was increased (alpha = 0.05) relative to hatch of nontreated eggs in all incubation solutions except zinc sulfate according to Dunnett's Test. Hatch in zinc sulfate was similar among all surface disinfestants except mercuric chloride, where hatch was reduced relative to hatch of nontreated and other surface disinfestant-treated eggs.

In-vitro Assays of Meloidogyne incognita and Heterodera glycines for Detection of Nematode-antagonistic Fungal Compounds

In-vitro methods were developed to test fungi for production of metabolites affecting nematode egg hatch and mobility of second-stage juveniles. Separate assays were developed for two nematodes: root-knot nematode (Meloidogyne incognita) and soybean cyst nematode (Heterodera glycines). For egg hatch to be successfully assayed, eggs must first be surface-disinfested to avoid the confounding effects of incidental microbial growth facilitated by the fungal culture medium. Sodium hypochlorite was more effective than chlorhexidine diacetate or formaldehyde solutions at surface-disinfesting soybean cyst nematode eggs from greenhouse cultures. Subsequent rinsing with sodium thiosulfate to remove residual chlorine from disinfested eggs did not improve either soybean cyst nematode hatch or juvenile mobility. Soybean cyst nematode hatch in all culture media was lower than in water. Sodium hypochlorite was also used to surface-disinfest root-knot nematode eggs. In contrast to soybean cyst nematode hatch, root-knot nematode hatch was higher in potato dextrose broth medium than in water. Broth of the fungus Fusarium equiseti inhibited root-knot nematode egg hatch and was investigated in more detail. Broth extract and its chemical fractions not only inhibited egg hatch but also immobilized second-stage juveniles that did hatch, confirming that the fungus secretes nematode-antagonistic metabolites.

Degree-day Models for Predicting Egg Hatch and Population Increase of Criconemella xenoplax

A degree-day model was derived to predict egg hatch for Criconemella xenoplax. Eggs collected from gravid females were incubated in distilled water at constant temperatures of 10-35 C. Sixty-six percent of all eggs hatched between 13 and 32 C, and 42% hatched at 10 C. All eggs aborted above 32.5 C. Between 25 and 32 C, 8.5 +/- 0.5 days were required for egg hatch. Degree-day requirement for egg hatch at 10-30 C was estimated to be 154 +/- 5 with a base of 9.03 +/- 0.04 C. This base of 9 C was adopted in studies of the relationship between degree-days and nematode population increase on Prunus seedlings grown 9-11 weeks in a greenhouse. Degree-day accumulations were based upon daily averages from maximum and minimum air temperatures. Ratios of final to initial population densities exhibited an exponential pattern in relation to degree-day accumulations with proportionate doubling increment of 0.100 +/- 0.049 every 139 +/- 8 degree-days. These results provide a means of predicting nematode population increase under greenhouse conditions and a basis for choosing sampling intervals when evaluating nematode multiplication.

Relationship Between Egg Viability and Population Densities of Meloidogyne incognita on Cotton

Cotton seedlings were inoculated with a range of initial populations (Pi) of Meloidogyne incognita in greenhouse experiments to test the relationship between nematode population densities and egg viability. In two of three experiments, a significant (P < 0.05) negative linear relationship was detected between percentage of hatch of first generation eggs and log Pi. A similar relationship between hatch and root-gall index was observed. In two experiments numbers of eggs judged to be nonviable based on appearance were significantly greater (P < 0.05) in the highest Pi (60,000 eggs/seedling) treatments than in treatments with lower Pi (600-6,000 eggs/seedling). It was concluded that Pi affects egg viability measured as percentage of hatch and that this relationship may play a role in the density-dependent winter survival rates of Meloidogyne species.

Development of the False Root-knot Nematode, Nacobbus aberrans, on Sugarbeet

The duration of the embryogenic development of Nacobbus aberrans (= N. batatiformis) took 9-10 days at 25 C and 51 days at 15 C. The J molted in the egg; hence the Je emerged from the egg. The effect of distilled water attd root leachates of kochia and sugarbeet was investigated at 5, 10, 15, 20, and 25 C. Root leachates did not significantly affect the percent of cumulative hatch of eggs, but temperature did significantly affect emergence of juveniles (p = 0.05). Less than 1, 5, and 20% of eggs hatched at 5, 10, and 15 C, respectively. The percent of cumulative hatch at 20 C was four times greater than at 15 C, while the highest percentage of juveniles emerged at 25 C. The duration of postembryogenic development from J inoculation until the appearance of mature females with egg masses took 38 days, and the life cycle from egg to egg was completed in 48 days at 25 C. All immature stages, young females and males were migratory endoparasites. Young females were able to leave the root swellings, where they developed from juvenile stages, and re-enter the root, where they formed a true gall and became sedentary. Thirty days after inoculation with J nematodes, specimens were detected in root tissues at 10, 15, 20, 25, and 30 C, hut not at 5 C. Five days after inoculation at 23 C ( +/- 2 C), juveniles had penetrated the roots and caused slight swellings of the tip and axis of sugarbeet feeder roots. Large cavities extended from the cortical parenchyma to the periphery of the stelar area, and 50 % of the central cylinder was destroyed 25 days after inoculation at 23 C. No syncytia formation were detected in the sugarbeet root swellings infected with juveniles. Syncytia were associated only with adult females; hyperplasia, abnormal proliferation of lateral roots, and asymmetry of root structure were additional anatomical changes induced by adult females. Only very smooth annules but no cuticular ornamentations were noted by SEM on the perineal area of adult females.