Carbohydrate Suppresses Parasitization and Induces Egg Retention in Trichogramma

Abstract: Laboratory experiments with Trichogramma principium suggest that Trichogramma females may be in one of two alternative states: the parasitization state or the egg retention state. Dissections show that T. principium females at emergence have ≅ 20 mature ovarian eggs. Females in egg retention state have practically the same mean number of mature ovarian eggs, while the distribution is different, suggesting that both oosorption and oogenesis may occur during egg retention. In parasitizing females, additional maturation starts simultaneously with the oviposition. However, ovipositing females tend to lay eggs with maturation, which is why they mostly carry few (< 5) mature ovarian eggs. The mean number of eggs laid during the first 48 h of the oviposition does not depend on whether the parasitization is delayed or not, suggesting that egg retention is connected just with oviposition behaviour rather than with the intensity of oogenesis. We conclude that ‘voluntary’ egg retention in the presence of a host does not differ with the state of ovaria from ‘forced’ egg retention under host deprivation. Supposedly, egg retention with the availability of a suitable host may be considered as a sort of short‐term adult diapause‐like state when not oogenesis, but oviposition is subject to hormonal regulation.

Examinations were carried out on the influence of the quality of larval food substances on the duration of aquatic stage, wing length and autogenous reproduction of Culex pipiens molestus and hybrids of C. p. molestus and C. p. pallens, using the laboratory colonies. Three kinds of larval diets, (A) 3 parts of laboratory chow for insect and 1 part of powdered yeast, (B) powdered yeast aloned and (C) 3 parts of potato starch and 1 part of powdered yeast were used. Fifty larvae of each strain or hybrid just hatched out were put into a glass jar containing 25mg of one of the three diets suspended in 300ml tap water. The larvae were transported everyday to a newly prepared jar with the diet of 50mg, 75mg, and 100mg on the 2nd, 3rd, 4thdday and after, respectively. Females were dissected on the 4th day after emergence. Developmental rate and mean of wing length of each strain or hybrid were maximum in diet A and minimum in diet C. In molestus, the percentages of females with mature eggs were 95.6 to 100,78.3 to 88.9 and 39.2 to 70.9 and the mean numbers of mature eggs in the females were 86.1 to 112.1,59.6 to 70.5 and 24.9 to 45.7 in diet A, B, and C respectively. In hybrids, the percentages of females with mature eggs were a little lower than those of molestus in each diet, while the mean number of the eggs were nearly the same as in molestus.

Plagiorchis elegans eggs were incubated at 0, 4, 10, 20, or 30 C under a 12-hr:12-hr (L:D) photoperiod for 120 days. Approximately one-quarter of the eggs had already initiated the process of embryonation when passed with the feces of the hamster (Mesocricetus auratus), the experimental definitive host. Eggs failed to embryonate at 0 C and died within 2 days. Incubation at 4 C allowed full embryonation, but the mean number of embryonated eggs per day (1.32+/-0.15) and the mean number of eggs available over the course of incubation (egg days) (219.00+/-2.24) remained low. These values increased progressively as incubation temperatures rose and reached levels of 3.59+/-0.30 and 1,467.50+/-4.56, respectively, at 20 C. Although incubation at 30 C further increased the mean number of eggs per day (5.45+/-0.56), the mean number of egg days declined sharply to 735.25+/-4.71, suggesting that elevated temperatures enhanced embryonation but lowered the survival of embryonated eggs. This was also reflected in the infectivity of eggs over time. Embryonated eggs incubated at 10 and 20 C remained infective significantly longer than eggs incubated at higher or lower temperatures. Incubation in constant light yielded significantly lower mean numbers of embryonated eggs per day (1.86+/-0.09) and mean number of egg days (96.25+/-0.99) than incubation in constant darkness (2.23+/-0.17 and 701.50+/-2.86 eggs, respectively) but did not affect the infectivity of embryonated eggs. The data suggest that at moderate temperatures and shielded from light, fully embryonated eggs of P. elegans may survive in the aquatic environment for a period of months. Such eggs may serve as a source of infection for populations of Stagnicola elodes and ensure the sustained production of the highly entomopathogenic cercariae required for mosquito control.

Approximately three decades ago the question was first answered "whether parasitoids are able to assess the number or origin of eggs in a host" for a solitary parasitoid, Leptopilina heterotoma, by fitting theoretically derived distributions to empirical ones. We extend the set of different theoretically postulated distributions of eggs among hosts by combining searching modes and abilities in assessing host quality. In the models, parasitoids search either randomly (Poisson) (1) or by vibrotaxis (Negative Binomial) (2). Parasitoids are: (a) assumed to treat all hosts equally, (b) able to distinguish them in unparasitised and parasitised hosts only, (c) able to distinguish them by the number of eggs they contained, or (d) able to recognise their own eggs. Mathematically tractable combinations of searching mode (1 and 2) and abilities (a,b,c,d) result in seven different models (M1a, M1b, M1c, M1d, M2a, M2b and M2c). These models have been simulated for a varying number of searching parasitoids and various mean numbers of eggs per host. Each resulting distribution is fitted to all theoretical models. The model with the minimum Akaike's information criterion (AIC) is chosen as the best fitting for each simulated distribution. We thus investigate the power of the AIC and for each distribution with a specified mean number of eggs per host we derive a frequency distribution for classification. Firstly, we discuss the simulations of models including random search (M1a, M1b, M1c and M1d). For M1a, M1c and M1d the simulated distributions are correctly classified in at least 70% of all cases. However, in a few cases model M1b is only properly classified for intermediate mean values of eggs per host. The models including vibrotaxis as searching behaviour (M2a, M2b and M2c) cannot be distinguished from those with random search if the mean number of eggs per host is low. Among the models incorporating vibrotaxis the three abilities are detected analogously as in models with random search. Experiments with two species of solitary parasitoids (L. heterotoma and Asobara tabida) are conducted. All theoretically postulated distributions are separately fitted to the resulting experimental egg distributions. The AIC criterion is used to choose the best fitting theoretical distribution. For both parasitoid species the frequency distribution of best fitting models for experimental data is compared to the classification of distributions generated by simulations. This leads to the conclusion that both L. heterotoma and A. tabida are able to distinguish between parasitised and unparasitised hosts. For L. heterotoma the results point to an ability to assess the number of eggs in a host, whereas A. tabida does not seem to have this ability. This difference suggests that an egg is more valuable for L. heterotoma than for A. tabida.

The effect of photoperiod on parasitization of the eggs of the Angoumois grain moth, Sitotroga cerealella (Olivier, 1789) by Trichogramma principium Sugonyaev & Sorokina, 1976 was investigated under several photoperiodic regimes of L : D = 3 : 21, 6 : 18, 9 : 15, 12 : 12, 15 : 9, 18 : 6 and 21 : 3. In all regimes, certain wasps delayed ovipositing in this non-preferred host. Potential fecundity of T. principium females (the number of mature ovarial eggs at emergence) and subsequent oogenesis (estimated by the number of mature ovarial eggs in non-ovipositing females) was independent of photoperiod. However, the percentage of females that oviposited was higher for females that developed and were kept under 6-12 h long photophase than for those that developed and were kept under ultra short (3L : 21D) and under long (18L : 6D and 21L : 3D) photophases. The average duration of the pre-oviposition (egg retention) period showed the opposite pattern to the photoperiodic response. A possible explanation of this reaction is that the delay in oviposition is adaptive if the probability of finding a better host is high. In autumn, when the last Trichogramma females are still active but their lepidopteran hosts are already much less abundant, then parasitization of any suitable host is the best strategy.

The use of anti mullerian hormone in the evaluation of egg donors

Egg load of newly emerged adult parasitoids of the southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), was examined. Infested bark was collected from D. frontalis infestations in southwestern Arkansas (Clark and Montgomery counties; 1995), the Bankhead National Forest in Alabama (1999), and the Talladega National Forest in Alabama (1998–2000) between June and September of each collection year. Newly emerged parasitoid females were dissected and numbers of mature and immature eggs counted. There was no significant difference in number of eggs within a species and between parasitoids from the Bankhead National Forest compared with those from the Talladega National Forest in Alabama in 1999. There were differences in number of eggs within a species between years at the same location. Dendroctonus frontalis parasitoids in the family Pteromalidae (Hymenoptera) had the most mature eggs, followed by Braconidae (Hymenoptera) and Eurytomidae (Hymenoptera). Within the D. frontalis parasitoids in the family Pteromalidae, Dinotiscus dendroctoni (Ashmead) and Heydenia unica Cook and Davis had more mature eggs than did Roptrocerus xylophagorum Ratzeburg. Within the D. frontalis parasitoids in the family Braconidae, Meteorus hypophloei Cushman females contained the most mature eggs, followed by Dendrosoter sulcatus Muesebeck, Spathius pallidus Ashmead, and Coeloides pissodis (Ashmead). These data constitute a foundation for defining baseline egg load of the D. frontalis parasitoid complex.

In order to assess the effects of schistosomiasis in the prostate gland, seminal vesicles, and the intra-abdominal protion of the vas deferens, we examined these organs at 200 consecutive autopsies of African males. Portions of these organs, as well as of the bladder, were digested in KOH; the proportion of eggs of Schistosoma haematobium found in these organs was: seminal vesicles, 54.5%; spermatic duct, 39.9%; and prostate gland, 20.5%. Eggs of Schistosoma mansoni were rarer in these tissues (bladder, 1%; seminal vesicles, 15.5%; spermatic duct, 8%; and prostate gland, 1%). The mean number of S. haematobium eggs per gram of tissue was substantially greater than for S. mansoni. To compare the histologic technique with that of digestion of tissue, we studied a further 100 consecutive autopsies—77% showed evidence of schistosomiasis by one or the other method. The bladder was affected in 65%; prostate gland, 21%; seminal vesicles, 70%; and the vas deferens in 42%. The detection of schistosomiasis was almost as good by the traditional histologic as by the digestion technique. Neither method revealed all infections. The frequency and severity of the lesions in these tissues was studied by standard histologic technique; tissues from the last 100 consecutive cases showed definite inflammatory lesions, especially in the seminal vesicles, but less than in the prostate gland. In none, however, was the reaction marked. There was good correlation between the mean number of eggs by the histologic and digestion methods, the exception being the prostate gland. No correlation could be shown between the number of eggs and inflammation: only a few eggs may provoke a marked response, or the reverse may occur. However, when inflammatory reaction was present, the average number of eggs per field was higher in every organ. Eggs were found mainly in the muscle layer of the seminal vesicles, but not uncommonly they were present in the mucosa and even in its lumen. The number of eggs did not vary much with the age of the infected person, but after the age of 60 years, the mean number of eggs in the bladder and the seminal vesicles dropped markedly.

We compared Walleye Sander vitreus egg retention among varying rock treatments placed in a hydraulic flume to test the influence of spawning substrate shape and size on egg retention and the influence of substrate siltation on egg adhesiveness. Egg loss from suboptimal spawning substrates has been hypothesized as a substantial source of mortality during the incubation period. To investigate the influence of substrate size and shape on Walleye egg retention, known numbers of Walleye eggs were pipetted onto rock substrate in a hydraulic flume and exposed to flowing water conditions. Eggs scoured from the substrate during each trial were collected and enumerated. Egg retention was higher in angular crushed limestone than in round glacial till and greater in coarse gravel than in larger size-classes, under all water velocity regimes. Angular coarse gravel had the highest egg retention rate (mean ± SD, 66.9 ± 3.7%), and round very coarse gravel had the lowest egg retention rate (47.0 ± 3.1%) of all the rock size and shape treatments. Substrate siltation significantly influenced egg adhesion. Clean rocks had a mean ± SD egg retention of 35.9 ± 36.6%, whereas fine-sediment-covered rocks did not retain any eggs throughout the course of the experiment. Differences in substrate size, shape, and siltation between Walleye spawning sites may contribute to variation in egg retention rates. Using angular gravel during the creation of Walleye spawning habitat and maintaining clean spawning substrates (through scouring effects and habitat restoration) may decrease mortality associated with egg entrainment and redistribution. Received June 13, 2012; accepted December 12, 2012

Laboratory experiments with Trichogramma principium Sug. et Sor. females that were offered Sitotroga cerealella Oliv. eggs demonstrated that less than half of the ovipositing females started oviposition during the first 2 days of the experiment, whereas the rest of the ovipositing females showed a delay in parasitization ranging from 2 to 10 days after contact with the host. Almost 10% of the wasps refused to parasitize the grain moth eggs over 12 days. The delay in parasitization may be as long as 6–8 days without any significant decrease in the number of mature ovarial eggs, in the number of eggs laid during the first 48 h of oviposition, and in the total lifetime fecundity. This egg retention is responsible for the fact that in spite of a relatively short mean duration of the oviposition period in each individual female (approximately 4 days), host parasitization by a group of simultaneously emerged wasps was almost uniformly distributed over 8–10 days. When induced, the parasitization state (i.e. the tendency to parasitize sequentially offered portions of host eggs) was stable both in the presence of a host and under host deprivation extended up to 8 days. These data provide further evidence for our hypotheses that the stability of the parasitization state in Trichogramma is based on endocrine mechanisms.

The purpose of this study was to determine whether preferred prey of Podisus macu- liventris (Say) (Heteroptera: Pentatomidae) adult females also conferred maximal fecundity. We also studied egg development and maturation as a function of predator age, i.e., ovigeny as used predominantly in the context of parasitoids. To determine prey preference, adult females were simultaneously offered Þve pest prey: 1) beet armyworm, Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae); 2) fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae); 3) cabbage looper, Trichoplusia ni (Hubner) (Lepidoptera: Noctuidae); 4) greater wax moth, Galleria mellonella (L.) (Lepidoptera: Pyralidae); and 5) yellow mealworm, Tenebrio molitor (L.) (Coleoptera: Tenebrionidae) (n 20). In a second experiment, adult P.maculiventris females were provided a single species of prey (for each of the Þve prey species, n 10). This experiment was repeated over four durations: 7, 15, 22, and 30d. After each time trial, egg load dissections were performed, and numbers of mature and immature eggs were recorded. P. maculiventris displayed a preference of beet army- worm, whether measured as numbers attacked or estimated biomass consumed. However, no signif- icant differences were found in cumulative numbers of eggs laid under the different prey treatments, with the exception of the 22-d trial where signiÞcantly more eggs were laid when feeding on the cabbage looper. During the 22-d trial, the number of egg clutches and numbers of eggs per clutch were highest when fed cabbage looper and lowest with yellow mealworm. Percentage of egg hatch combined across time trials was highest in cabbage looper (81.7%) and lowest in greater wax moth (63.8%). Egg load dissections revealed that the total number of eggs and numbers of mature eggs declined signiÞcantly with predator age. However, numbers of immature eggs increased. The mean number of mature eggs in 7-d-old predators represented only 5% of mean cumulative numbers of eggs laid by 30-d-old predators, indicating that P. maculiventris is strongly synovigenic, where egg development and maturation continues during adulthood. The implications of these results are discussed from the context of P. maculiventris as a biological control agent.

Pot culture experiments were conducted during kharif and rabi to study the oviposition and survival of leafhoppers and thrips on groundnut under caged conditions. Of the twenty five genotypes/varieties evaluated, CSMG 84-1 and ICGV 86522 (0.6 eggs) recorded lesser number of eggs as against ICG 7237 (2.8 eggs/terminal bud). The resistant genotypes had a mean of 1.27 ± 0.53 eggs, susceptible entries 2.18 ± 0.45 eggs and highly susceptible ones with 2.33 ± 0.33 eggs. The number of eggs laid by thrips ranged from 0.4 (ICG 5240 and ICGV 86522) to 2.0 eggs (TMV-2)/terminal bud. The resistant entries had mean number of eggs- 0.62 ± 0.24, moderately resistant ones- 1.00 ± 0.18, susceptible ones- 1.21 ± 0.41 and highly susceptible ones- 1.63 ± 0.34 eggs. The leafhopper survival was maximum in ICG 7237 (14.00/plant), and minimum in NCAc 343 (2.00/plant). The resistant genotypes recorded a mean survival of 5.17± 2.71 nymphs/plant, whereas, the moderately resistant ones had 8.33 ± 1.37 nymphs/plant, susceptible ones 9.42 ± 1.27 nymphs/plant, and highly susceptible ones with 10.8 ± 1.94 nymphs/plant. The thrips survival varied from 3.00 (ICGV 86522) to 12.00 (TMV-2)/plant, with the mean number of thrips being 4.50 ± 1.04, 6.66 ± 1.96, 8.85 ± 1.49 and 10.00 ± 1.41 thrips/plant in the resistant, moderately resistant, susceptible and highly susceptible genotypes, respectively. The sugars, phenols,tannins, and amino acids in the plant tissues, and the leaf morphological characters are also analysed and correlations brought out.

Ovitrap surveillance of Aedes vectors in Sri Lanka needs improvement to effectively monitor vector abundance in dengue high-risk areas and detect emerging infestation zones. A study was conducted in two dengue high-risk areas, Narahenpita and Battaramulla in the Western Province, to assess the influence of ovistrip texture, color, and water type on Aedes oviposition, while adhering to WHO guidelines. The relationship of OI and the mean number of eggs per trap with ovitrap designs were determined by General Linear Model (GLM), which revealed a significant difference in the OI between the two study sites (P=0.005), while the mean number of eggs per ovitrap did not differ significantly (P=0.134). Water type had no significant influence on OI and mean number of eggs per ovitraps. A significant effect of ovistrip type (F=6.73, P<0.001) was found on OI and mean egg per trap (F=9.85, P<0.001), where filter paper exhibited the largest coefficient in magnitude (-0.1698), indicating a strong negative correlation with OI and mean eggs per trap (-2.445) while white fabric showed a strong positive co-efficient magnitude with OI (0.1108) and mean egg per trap (1.605). According to Spearman's rank correlation, the rainfall did not have a statistically significant effect on the number of eggs collected or the OI. The study suggested that fabric ovistrips colored white combined with rainwater or tap water, make ovitraps highly effective for Aedes vector surveillance, while the currently used filter paper ovistrip having a negative effect on the egg number laid.

Summary Fluctuations in population density of Hyphantria cunea in Japan are characterized by a gradation‐like pattern. Analysis of the life table data taken from two stations during eight successive generations showed that (1) mortality during egg and early larval stages was density‐independent, (2) mortality during later larval stages was inversely density‐dependent, and (3) mortality during prepupal and pupal stages was density‐independent. Thus the overall mortality process from egg to adults eclosion was inversely density‐dependent. The inverse density‐dependence in mortality process during later larval instars was mainly attributed to the ‘escape’ (VOÛTE, 1946) of H. cunea populations from the predation pressure of polyphagous predators such as birds and Politses wasps. This inverse density‐dependence was considered to be a cause of gradation‐like fluctuation. Field collection of egg‐masses showed that the mean number of eggs per egg‐mass, which was believed to be a good representation of mean fecundity, varied from 425 to 1050 during 4 years. Density‐dependent reduction in the mean number of eggs per egg‐mass was demonstrated, and this reduction was a factor regulating the population density. Assuming fixed sex ratio and survival rate of adults, a preliminary population model was constructed. The number of eggs laid in the survey station could be predicted well by the model based on the number of eggs laid in the previous generation, in 9 out of 13 cases. An attempt to apply a model of the same type to mimic the fluctuation of abundance (peak number of larval colonies per tree) on road‐side trees suggested another density‐dependent process, that is, insecticide application by man. Discussion was also presented on the causes responsible for the turn of population trend from decreasing to increasing in the 1st generation of 1968.

Growth and other biological processes in aquatic organisms are particularly dependent on water temperatures. This study examined the effects of water temperature on the growth of Triops longicaudatus. The influence of water temperature fluctuations was that growth rate was increased at higher temperatures. The mean carapace length was 5.7 () mm in a water temperature of and 7.5 () mm in a water temperature of on the 14th day after submergence. It was 6.9 () mm in a water temperature of and 7.8 () mm in a water temperature of on the 21st day after submergence. The mean carapace length grew rapidly within 14 days after submergence, but increase in carapace length beyond this time was slow. The influence of water depth fluctuations was low as the mean carapace length was 9.3 () mm under a water depth of 80 mm and 9.5 () mm under a water depth of 190 mm on the 19th day after submergence. Biomass showed that the carapace length of 5, 10, 16 and 20 mm was a dry-weight of 1.1 (), 18.0 (), 26.0 () and 52.3 () mg respectively. The number of eggs increased rapidly with increments in carapace length. The mean number of eggs was 20 () at a carapace length of 7.0 mm, but at a carapace length of 17.0 mm, the mean number of eggs was 560 (). The results suggested that differences in water temperature accounted for the differences in length of the carapace and the number of eggs.