Fertility and life expectancy of the predator Supputius cincticeps (Heteroptera: Pentatomidae) exposed to sublethal doses of permethrin

The stinkbug Supputius cincticeps (St?l) (Heteroptera: Pentatomidae) can be found in agricultural and forest ecosystems feeding primarily on larvae of Coleoptera and Lepidoptera, where it can be exposed to insecticide applications. This study therefore aimed to evaluate the reproductive potential of S. cincticeps after exposition to sublethal doses of permethrin (5.74 x 10(-3), 5.74 x 10(-2), 5.74 x 10(-1), 5.74 and 57.44 ppb) through the use of a fertility life table. The development cycle of this predator was determined in order to calculate its net reproductive rate (R0), the infinitesimal (rm) and finite (lambda) rates of increase in addition to mean generation time (T). The net reproductive (18.31), infinitesimal (rm) (0.050) and finite (lambda) (1.051) rates of increase were higher, while generation time (57.93 days) was shorter for S. cincticeps exposed to 5.74 x 10(-1) ppb of permethrin than in the control. This indicates a higher rate of population increase of this predator when exposed to this permethrin dose.     

Effects of salinity, temperature and food level on the demographic characteristics of the seawater rotifer Synchaeta littoralis Rousselet

A strain of the seawater species Synchaeta littoralis, isolated from a Spanish Mediterranean coastal salt marsh, was cultured in the laboratory and fed with the alga Tetraselmis sp. The effect of three salinities (25 per thousand, 30 per thousand and 35 per thousand), two temperatures (20 degrees C and 25 degrees C) and two food levels (75,000 and 150,000 cells ml(-1)) on demographic parameters was studied using a life table approach. Average lifespan (LS) ranged between 4.0 and 7.3 days, net reproductive rate (R(0)) between 4.2 and 9.1 offspring per female, and intrinsic growth rate (r) between 0.50 and 0.95 day(-1). Salinity and temperature had a significant negative effect (***p<0.001) on both average lifespan (LS) and net reproductive rate (R(0)). Nevertheless, S. littoralis grew adequately at 35 per thousand (average value of r=0.67 day(-1)). Intrinsic growth rate also increased with temperature due to the lower value of the generation time (ranged between 2.3 and 3.8 days in all assays). Food level only had a significant negative effect (***p<0.001) on R(0). The experiments designed allowed us to know the basic demographic parameters of S. littoralis.     

Life tables of Habrobracon hebetor (Hymenoptera: Braconidae) parasitizing Anagasta kuehniella and Plodia interpunctella (Lepidoptera: Pyralidae): effect of host density

The reproductive performance of the parasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae) against the moths Anagasta kuehniella Zeller and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) was studied in the laboratory. The analysis was based on the comparison of parasitoid's life table parameters related to those of its hosts at various conditions of host density (daily supply of 1, 5, 15, and 30 full-grown host larvae). The estimated parameters were the intrinsic rate of natural increase (rm), the net reproductive rate (R0), the mean generation time (G), the finite capacity of increase (lambda), the gross reproductive rate (GRR), the doubling time (DT), the reproductive value (Vx), and the life expectancy (ex). The rm of H. hebetor proved to be significantly higher than those of its hosts at all host densities. When only one host per day was supplied, the wasp had the lowest reproductive potential, whereas it was maximized when 15 hosts per day were exposed. Maximum values of R0 and GRR were obtained at densities > or =15 host larvae per day. Any increase in host supply above this threshold did not cause significant changes in life table parameters. Variation of rm as a function of host density can be described by the linear regression. Sex ratio of wasp progeny (females/total) ranged from 0.36 to 0.42, irrespective of host density or species. Newly emerged adults recorded maximum ex and Vx. The results of this study can be used to improve mass rearing programs and inoculative release applications of H. hebetor against moth pests of stored products.     

氰氟虫腙对小菜蛾阿维菌素抗性和敏感种群的亚致死效应(英文)

在实验室条件下采用生命表技术研究了氰氟虫腙亚致死剂量（LC₂₅）对小菜蛾Plutella xylostella阿维菌素抗性（AV-R）和敏感（AV-S）种群的亚致死效应, 旨在为小菜蛾对阿维菌素的抗性治理提供理论基础。结果表明： 氰氟虫腙对小菜蛾3龄幼虫抗性种群的LC₅₀和LC₂₅分别为0.24 mg/L和0.09 mg/L; 对敏感种群的LC₅₀和LC₂₅分别为0.20 mg/L和0.07 mg/L。氰氟虫腙亚致死剂量0.09 mg/L 处理小菜蛾后, 对处理代的影响表现为显著降低处理种群的化蛹率、 蛹重、 羽化率、 繁殖力; 明显延长蛹期, 缩短成虫产卵期和寿命; 对子代种群的影响表现为显著降低卵的孵化率、 幼虫各龄期的存活率, 延长发育历期。处理种群的内禀增长率（r_m）、 周限增长率（λ）和净增值率（R₀）显著低于对照种群（P<0.0001）。亚致死剂量的氰氟虫腙对小菜蛾抗性种群的影响大于敏感种群, 对处理代种群的影响大于子代种群。氰氟虫腙亚致死剂量可以极大地影响小菜蛾尤其是阿维菌素抗性种群的种群动态, 因此氰氟虫腙对于小菜蛾的抗性治理具有积极的作用。     

温度和食物浓度对三品系萼花臂尾轮虫实验种群动态的影响

应用个体培养方法,研究了温度(20、25和30℃)和藻类食物浓度(1．5×10^6、3．0×10^6、6．0×10^6和9．0×10^6cells·ml^-1)对青岛、芜湖、广州三品系萼花臂尾轮虫种群动态的影响．结果表明,温度仅对轮虫的世代时间和种群内禀增长率有显著影响,而品系对所有生命表参数均无显著影响．轮虫种群的内禀增长率随培养温度的升高而增大,世代时间则随培养温度的升高而缩短．食物浓度仅对轮虫的生命期望值和平均寿命有显著影响,品系对轮虫的净生殖率、世代时间、生命期望值和平均寿命也有显著影响．三品系间,以广州品系轮虫的净生殖率、世代时间、生命期望值和平均寿命最大,芜湖品系最短．当食物浓度为3．0×10^6cells·ml^-1时,轮虫的生命期望值和平均寿命最长,9．0×10^6cells·ml^-1时最短．各品系轮虫的净生殖率、世代时间、总生殖率、生命期望值和平均寿命均随培养温度的升高而减小,广州品系的净生殖率除外．轮虫种群的内禀增长率和广州品系轮虫的总生殖率则随培养温度的升高而增大．青岛和广州品系轮虫的各生命表参数,均与食物浓度呈曲线相关,但芜湖品系仅世代时间、平均寿命和生命期望值随食物浓度的增大而缩短．     

Age-dependent fecundity and life-fertility tables for Podisus nigrispinus (Dallas) (Het., Pentatomidae)

Abstract: The reproductive potential and longevity of Podisus nigrispinus (Dallas) were determined under laboratory conditions at a constant temperature of 25°C. The data were used to calculate life-fertility tables and rates of increase. The fecundity plateau of P. nigrispinus lasted 18 days, and during this period mean fecundity was 8.89 eggs per female per day. It started at the eighth day of age and ended at the 18th day of age. The declining fecundity period started at 18 days of age and ended with the death of the females. The female of P. nigrispinus oviposited a mean of 188.54 eggs, and had a mean longevity of 31.21 days. The gross reproductive rate (GRR) was 104.374 females/female; the net reproductive rate ( R _o) was 31.945 females/female; the generation time was 47.390 days; the doubling time was 9.480 days; the intrinsic rate of increase ( r _m ) was 0.073, and the finite rate of increase ( λ ) was 1.076. The predator population increased by 16.61 adult progeny per female per generation in the laboratory.     

温度和食物浓度对三品系萼花臂尾轮虫实验种群动态的影响

应用个体培养方法,研究了温度(20、2和30 ℃)和藻类食物浓度(1.5×10₆、3.0×10₆、6.0×10₆和9.0×10₆ cells·ml^-1)对青岛、芜湖、广州三品系萼花臂尾轮虫种群动态的影响.结果表明,温度仅对轮虫的世代时间和种群内禀增长率有显著影响,而品系对所有生命表参数均无显著影响.轮虫种群的内禀增长率随培养温度的升高而增大,世代时间则随培养温度的升高而缩短.食物浓度仅对轮虫的生命期望值和平均寿命有显著影响,品系对轮虫的净生殖率、世代时间、生命期望值和平均寿命也有显著影响.三品系间,以广州品系轮虫的净生殖率、世代时间、生命期望值和平均寿命最大,芜湖品系最短.当食物浓度为3.0×10₆ cells·ml^-1时,轮虫的生命期望值和平均寿命最长,9.0×10₆ cells·ml^-1时最短.各品系轮虫的净生殖率、世代时间、总生殖率、生命期望值和平均寿命均随培养温度的升高而减小,广州品系的净生殖率除外.轮虫种群的内禀增长率和广州品系轮虫的总生殖率则随培养温度的升高而增大.青岛和广州品系轮虫的各生命表参数,均与食物浓度呈曲线相关,但芜湖品系仅世代时间、平均寿命和生命期望值随食物浓度的增大而缩短.     

Infectivity and reproductive potential of the Oswego strain of Heterorhabditis bacteriophora associated with life stages of the clover root curculio,Sitona hispidulus

The infectivity and reproductive potential of the entomopathogenic nematode Heterorhabditis bacteriophora (Oswego strain), at different concentrations, was studied. Seventy to 80.0% mortality to late instar larvae of the clover root curculio, Sitona hispidulus, and 40.0-76.0% mortality to pupae, was observed at concentrations of 15-100 infective juveniles. There were no significant differences in mortality among nematode concentrations. LC(50) levels of 4.0 and 21.4 nematodes were determined for clover root curculio larvae and pupae, respectively. Nematodes did not cause significant mortality to adult or first instar clover root curculio. H. bacteriophora was able to complete its development and reproduce in 74.0-95.0% of clover root curculio late instar larvae and pupae. Reproductive potential in curculio larvae and pupae ranged from 0 to 7040 infective juveniles per host. Larvae exposed to 100 nematodes had a reproductive potential significantly higher than in those larvae exposed to 15 and 50 nematodes. Reproductive potential in pupae decreased with an increased nematode dose, indicating potential crowding effects. Host larval and pupal mass were positively correlated with nematode progeny production.     

The impact of refugia on the development of thiabendazole resistance in Haemonchus contortus

Martin P. J., Le Jambre L. F. and Claxton J. H. 1981. The impact of refugia on the development of thiabendazole resistance in Haemonchus contortus. International Journal for Parasitology11: 35–41. Beginning with a mixture of 5% thiabendazole-resistant and 95% non thiabendazole-resistant Haemonchus contortus larvae, worm free sheep were artificially infected with either 10,000, 9000, 7000, 2500 or zero larvae. Four weeks later, the infected sheep were treated with 44 mg/kg of thiabendazole. Seven days after anthelmintic treatment the same sheep were infected with zero, 1000, 3000, 7500 or 10,000 larvae respectively so that each sheep was given a total of 10,000 larvae. The larvae given after thiabendazole treatment are referred to as being in refugia (defined as an area where individual members of a population can escape exposure to a drug). This was repeated for six generations of parasites, maintaining the same proportion of larvae in refugia in each generation. The egg hatch assay for resistance indicated that refugia delayed the development of resistance in Haemonchus contortus. Where none or a small proportion of larvae were in refugia, a rapid increase in resistance occurred. With an increased proportion of larvae in refugia, resistance was slower to develop. Population size, as estimated by faecal egg counts done after anthelmintic treatment and corrected for the number of larvae given in each treatment, was lower at the higher levels of refugia. This was due to a lower level of resistance in the higher refugia lines and consequently a greater effect of the drug. However, the estimate of population size, from egg counts done after the larvae introduced from refugia had matured, were similar in all lines.     

Bionomics of Opius bellus (Hymenoptera: Braconidae), an endoparasitoid of Anastrepha fraterculus (Diptera: Tephritidae) in fruit-growing areas of Northwestern Argentina

Opius bellus is a neotropical larval-prepupal parasitoid known to attack the pestiferous fruit fly, Anastrepha fraterculus. Due to interest in the use of native parasitoids in forthcoming fruit fly biocontrol programmes in Argentina, O. bellus was colonised for the first time using laboratory-reared A. fraterculus larvae. A series of experiments were conducted to (1) best achieve an efficient parasitoid rearing by determining optimal larval host age, host:parasitoid ratio and host exposure time and (2) assess their potential as biological control agents by determining reproductive parameters. The most productive exposure regimen was: 7–9 d-old (early and middle third-instars) A. fraterculus larvae for 4 h at a 4:1 host:parasitoid ratio; this array of factors was sufficient to achieve the highest average adult emergence (48%) and an offspring sex ratio at equitable proportion. Increasing both host:parasitoid ratio further than 4:1 and the host exposure time beyond 4 h did not significantly enhance parasitoid female offspring yield. Females produced eggs for 29.5 ± 1.4 days. At 32 days of age, 50% of the females were still alive. The majority of the progeny were produced by females between 20 and 24 d-old. At 26°C, gross fecundity rate, net reproductive rate, intrinsic rate of increase and mean generation time were 20.7 ± 4.2 offspring/female, 9.6 ± 2.5 females/newborn females, 0.06 ± 0.01 females/female/day and 8.4 ± 0.2 days, respectively. The long lifespan and reproductive parameters suggest that this parasitoid species has suitable attributes for mass-rearing.     

Susceptibility of the Plum Curculio,Conotrachelus nenuphar,to Entomopathogenic Nematodes

The plum curculio, Conotrachelus nenuphar, is a major pest of pome and stone fruit. Our objective was to determine virulence and reproductive potential of six commercially available nematode species in C. nenuphar larvae and adults. Nematodes tested were Heterorhabditis bacteriophora (Hb strain), H. marelatus (Point Reyes strains), H. megidis (UK211 strain), Steinernema riobrave (355 strain), S. carpocapsae (All strain), and S. feltiae (SN strain). Survival of C. nenuphar larvae treated with S. feltiae and S. riobrave, and survival of adults treated with S. carpocapsae and S. riobrave, was reduced relative to non-treated insects. Other nematode treatments were not different from the control. Conotrachelus nenuphar larvae were more susceptible to S. feltiae infection than were adults, but for other nematode species there was no significant insect-stage effect. Reproduction in C. nenuphar was greatest for H. marelatus, which produced approximately 10,000 nematodes in larvae and 5,500 in adults. Other nematodes produced approximately 1,000 to 3,700 infective juveniles per C. nenuphar with no significant differences among nematode species or insect stages. We conclude that S. carpocapsae or S. riobrave appears to have the most potential for controlling adults, whereas S. feltiae or S. riobrave appears to have the most potential for larval control.     

Propagation of tomato spotted wilt virus in Frankliniella occidentalis does neither result in pathological effects nor in transovarial passage of the virus

The effect of tomato spotted wilt virus (TSWV) on Frankliniella occidentalis Pergande (Thysanoptera; Thripidae) following a 6-hour acquisition access period on infected plants was investigated. No statistically significant differences were observed among viruliferous, non-viruliferous and control thrips with respect to developmental time, reproduction rate and survival. Thrips larvae, exposed or non-exposed to TSWV, developed from egg to adult in 13.1 and 13.2 days, respectively. Exposed females produced an average of 28.3 larvae whereas control thrips produced 22.3 larvae and longevity was 13.4 and 12.5 days, respectively. None of these values were significantly different. Population reproductive statistics, net reproductive rate (R ₀), mean generation time (T) and intrinsic rate of increase (r _m) were calculated from the life fertility tables. R ₀ and r _m were higher for viruliferous thrips as compared to non-viruliferous and non-exposed thrips. Virus transmission studies revealed that viruliferous thrips were able to transmit virus until death and that TSWV was not transovarially transmitted.     

麦长管蚜抗吡虫啉品系和敏感品系的生殖力比较

通过建立抗性品系和敏感品系的种群生命表,比较麦长管蚜Sitobion avenae(Fabricius)抗吡虫啉品系和敏感品系的生殖力差异,结果表明,抗性品系适合度显著下降,世代历期延长,成蚜寿命缩短;在繁殖上表现为产仔量下降,生殖期缩短。以净生殖率(R0)和内禀增长率(rm)来评价抗性品系的相对生物适合度,抗性品系分别是敏感品系的0.5200和0.7481。因此,麦长管蚜对吡虫啉的抗性品系存在显著的生殖劣势。     

Age at Which Larvae Are Orphaned Determines Their Development into Typical or Rebel Workers in the Honeybee (Apis mellifera L.)

In the honeybee, diploid larvae fed with royal jelly develop into reproductive queens, whereas larvae fed with royal jelly for three days only and subsequently with honey and pollen develop into facultatively sterile workers. A recent study showed that worker larvae fed in a queenless colony develop into another female polyphenic form: rebel workers. These rebel workers are more queenlike and have greater reproductive potential than normal workers. However, it was unclear whether larvae orphaned at any time during their feeding period can develop into rebels. To answer this question, the anatomical features of newly emerged workers reared in queenless conditions at different ages during the larval period were evaluated. Our results showed that larvae orphaned during the final four or more days of their feeding life develop into rebel workers with more ovarioles in their ovaries, smaller hypopharyngeal glands, and larger mandibular and Dufour’s glands compared with typical workers with low reproductive potential that were reared with a queen or orphaned at the third to last or a later day of feeding life.     

Trade-off between mobility and fitness in Cydia pomonella L. (Lepidoptera: Tortricidae)

Abstract.  1. The codling moth Cydia pomonella , one of the most important pest insects of apple fruit orchards worldwide, is regarded as a 'sedentary' insect, but the natural populations consist of both mobile and sedentary genotypes that display different dispersal capacity in the field. The current study investigated whether there is a fitness consequence of being mobile in this species by comparing two strains with contrasting levels of mobility obtained through bi-directional selection.
2. Female moths of the sedentary strain were significantly larger, laid more eggs during their lifespan, and both male and female moths of this strain lived longer, when compared with the mobile strain.
3. The age-specific fecundity of female moths from the sedentary strain was significantly greater, in particular between 3 and 5 days after emergence when the peaks of both oviposition and flight capacity occur, relative to the mobile moths, thereby leading to a greater reproductive function.
4. These differences resulted in different demographic parameters between the two strains. The sedentary strain had a significantly greater net reproductive rate ( R _o ) and a higher intrinsic rate of natural increase ( r _m ), although the generation time ( T ) was similar, hence requiring a shorter time to double the population size, in comparison to the mobile strain.
5. This study provides empirical evidence for the cost of being mobile in C. pomonella . Trade-offs between mobility and fitness might have contributed to the existence of genetic variance for dispersal behaviour in the natural populations and the maintenance of relative sedentariness in the species.     

Influence of plant polymers on the distribution and cultivation of bacteria in the phylum Acidobacteria

Members of the phylum Acidobacteria are among the most abundant bacteria in soil. Although they have been characterized as versatile heterotrophs, it is unclear if the types and availability of organic resources influence their distribution in soil. The potential for organic resources to select for different acidobacteria was assessed using molecular and cultivation-based approaches with agricultural and managed grassland soils in Michigan. The distribution of acidobacteria varied with the carbon content of soil: the proportion of subdivision 4 sequences was highest in agricultural soils (ca. 41%) that contained less carbon than grassland soils, where the proportions of subdivision 1, 3, 4, and 6 sequences were similar. Either readily oxidizable carbon or plant polymers were used as the sole carbon and energy source to isolate heterotrophic bacteria from these soils. Plant polymers increased the diversity of acidobacteria cultivated but decreased the total number of heterotrophs recovered compared to readily oxidizable carbon. Two phylogenetically novel Acidobacteria strains isolated on the plant polymer medium were characterized. Strains KBS 83 (subdivision 1) and KBS 96 (subdivision 3) are moderate acidophiles with pH optima of 5.0 and 6.0, respectively. Both strains grew slowly (μ = 0.01 h(-1)) and harbored either 1 (strain KBS 83) or 2 (strain KBS 96) copies of the 16S rRNA encoding gene-a genomic characteristic typical of oligotrophs. Strain KBS 83 is a microaerophile, growing optimally at 8% oxygen. These metabolic characteristics help delineate the niches that acidobacteria occupy in soil and are consistent with their widespread distribution and abundance.     

Transmission of Rickettsia massiliae in the tick, Rhipicephalus turanicus

Rickettsia massiliae, strain Bar29, was detected in engorged female ticks of the Rhiphicephalus sanguineus group collected in Corsica, a French Mediterranean island. Ticks were identified by molecular analysis as Rhipicephalus turanicus (Pomerantsev) (Acari: Ixodidae). Twenty larvae of the second generation obtained from a R. massiliae-infected, engorged female were tested by polymerase chain reaction (PCR) and all were positive for R. massiliae. Larvae of the same cohort were fed on rabbits and specimens of subsequent stages of the second and third generation of ticks were tested by PCR. Both transovarial and transstadial transmission were demonstrated; the transovarial transmission rate was estimated at 100%. A high filial infection rate was demonstrated; 132 out of 134 larvae obtained from five infected females of the fourth generation were infected. When saliva samples from half-engorged Rh. turanicus of the second generation were tested by PCR, four out of five were positive. Rickettsia massiliae was detected in faeces of infected ticks by PCR and immunofluorescence assay, although no rickettsiae could be maintained in culture. Co-feeding/transsexual transmission of R. massiliae Bar29 was demonstrated by feeding male Rh. turanicus on a rabbit with Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae) females (the latter were the only uninfected ticks available). Infection was subsequently detected in nine out of the thirteen females (69.2%). These results suggest that Rh. turanicus ticks are potential vectors and reservoirs for R. massiliae Bar29.     

Response to ivermectin treatment of parasitic stages of Haemonchus contortus resistant or susceptible to ivermectin.

Two groups of 33 helminth-naive lambs were infected with 5,000 L3 of an ivermectin-resistant or -susceptible strain of Haemonchus contortus (groups R and S). On days 6, 10, 16, and 21 postinfection, 5 animals from each group were chosen at random and orally treated with 0.2 mg/kg of ivermectin. On each occasion, 2 randomly selected lambs from each group were also killed to determine the number and stage of development of the worms present at the time of treatment. These necropsies revealed that by day 6 early and late fourth-stage larvae were present, whereas on day 10 the early fifth stage had been reached; by days 16 and 21 all worms had reached the adult stage. Necropsies on day 28 postinfection revealed that although animals treated at day 6 had 26.3% fewer worms than the controls, there was no significant difference (P greater than 0.05) between worm burdens from any of the animals infected with the R strain and treated at different times after infection when compared with the untreated controls. With ivermectin significant reductions were obtained in the worm burdens of the animals infected with the susceptible strain; these were reduced by 96% when treatment was given on day 6 against fourth-stage larvae and 98.9% when the drug was given on day 21 against adult stages. From these results it is clear that resistance to ivermectin in this strain of H. contortus is present as early as the fourth larval stage.     

Characterization of a strain of Serratia sp. with ixodicide activity against the cattle tick Rhipicephalus microplus

Cattle ticks are considered the most important ectoparasite in the livestock industry. Rhipicephalus microplus causes economic losses both through direct feeding on livestock and through disease transmission. Reports of the failure of chemical ixodicides to control this tick have led to a search for control alternatives, such as bacteria with ixodicide activity. The objective of this work was to select a bacterial strain with ixodicide activity against R. microplus. In total, 83 bacterial strains were isolated from soil and dead R. microplus specimens, and all strains were evaluated against larvae in a screening test. Bacteria with ixodicide activity were evaluated in larvae and engorged adult female ticks. The larvae were challenged using the larval immersion test (LIT) with 20 µg/mL total protein. The median lethal concentration (LC₅₀) for larvae was obtained by using nine total protein concentrations. Engorged adult female ticks were challenged using the adult immersion test (AIT) with six protein concentrations. We evaluated adult mortality on day 10, oviposition rate on day 14 and hatching rate on day 40 after challenge. Only one bacterial strain (EC-35) showed ixodicide activity against larvae and adult R. microplus. The highest larval mortality, 52.3%, occurred with a total protein concentration of 40 μg/mL, and the LC₅₀ was 13.9 µg/mL of protein. In adults, a total protein concentration of 10 µg/mL had the highest mortality (55%), oviposition inhibition (50.9%) and reproductive potential inhibition (52.5%). However, there was no significant effect on hatching. The 16S rRNA gene sequence showed 99% identity of EC-35 with Serratia sp.

     

Effect of x-irradiation on the formation of the puparium in the fleshfly, Sarcophaga bullata

Post-feeding, pre-critical stage larvae (36 hr before pupariation) of Sarcophaga bullata were exposed to X-rays and the effects on pupariation observed. With doses ranging from 1250 to 10,000 R the prepuparial period was prolonged and the duration of this delay increased with higher doses. Doses above 2500 R inhibited the retraction of anterior segments, longitudinal contraction and cuticular shrinkage resulting in larval-like tanned puparia. With the anterior part of the body shielded during irradiation, normal puparia were formed, but after a delay proportional to the area irradiated. Injection of β-ecdysone counteracted this delay. With the doses used, irradiation had no effect on post-critical stage larvae. This suggested that the CNS has a special mechanism which controls the neuromuscular processes of pupariation, and when this mechanism is damaged by irradiation larval-like puparia are formed. The pupariation delay was attributed to a temporary block in the synthesis, or release, or both of α-ecdysone (in whole-body or anteriorly only irradiated larvae) and its final conversion to β-ecdysone (in posteriorly only irradiated larvae). The fact that post-critical stage larvae are insensitive to irradiation suggests that the neuromuscular and neurosecretory processes which are affected by irradiation are already completed at that stage.