3.1. Development time
The development time of O.
pityocampae did not significantly differ by gender (t=-1.78; df=54; p=0.8),
and mean egg-to-adult (total)
development time of O. pityocampae was
11.68±0.07 and 11.84±0.06
days for male and female parasitoids,
respectively. Mean egg, larval, and pupal development time of O. pityocampae
were 1.94±0.01, 3.42±0.03, and 7.11±0.03, respectively.
3.2. Longevity of O.
The effect of food on longevity of
female O. pityocampae (F=56.32, df=3, p < 0.001) and male O. pityocampae (F=276.46, df=3, p <0.001) was meaningful in terms of the longevity of wasps fed with honey and water diet, and only honey diet was significantly higher than control for both males and females (p < 0.001). There was no significant difference in the female wasps longevity fed with honey and water and just honey (T=0.94, df=56, p >
0.05 Table 1). When exposed to the honey and B. signatum egg, the mean
longevity of O. pityocampae females was estimated to be 19.81 days
(Table 1). The longevity of both male and female O. pityocampae was
significantly affected by the feeding regime (F=4.41, df=1, p <0.053, Table 1). The longevity of water-fed wasps was significantly lower than that of the wasps fed with honey for both males and females (F=91.56, df=3, p <0.001, Table 1). The longevity of female O. pityocampae whose feeding regime was based on host dependent resources such as host feeding was significantly higher than that of female wasps fed with water and significantly lower than that of wasps fed with honey (F=90.87, df=2, p <0.001, Table 1). The adult parasitoids disappeared shortly after emerging in the non-food environment, which shows the important role of nutrition in increasing adult parasitoids longevity. Other than this diet, there is no difference between genders of O. pityocampae (T=-1.60, df=40, p > 0.05, Table 1).
3.3. Parasitism percentage of O. pityocampae
Parasitism is very low in the
first 24 hours of parasitoid life span and parasitizing B. signatum eggs (7.27±2.54 eggs) at low levels. Understanding the efficient age of parasitoids is very
important to obtain effective and successful parasitism in field release
programs as well as for mass production. The maximum number of eggs deposited by
one O. pityocampae female was
observed on the 3rd (39.27±0.01
eggs) days of its adult life span. The egg laying period
of O. pityocampae lasted 14.45±0.68 days (Fig.
1). A female O. pityocampae lays 122.45±4.30 eggs in its whole life time. The average
adult longevity was 9.09±0.74 and
19.81±0.62 days for females and males, respectively.
3.4. Sex ratio of O.
Sex ratio of O. pityocampae on B. signatum eggs in the laboratory
is shown in Fig. 2. The sex ratio (female: male) of O.
pityocampae is 4.2:1.
4.1. Development time
According to many researchers,
there are different types of development times
in Ooencyrtus species at different temperatures and in different hosts.
For example, Rahim et al. (20) studied the effect of temperature on the development time of O. papilionis.
Ashmead showed that in this parasitoid no development of
immatures occurs if the temperature is over 32.5°C. According to the survey by
Muesebeck and Dohanian (18) in both O. kuvanae and O. anasae development from egg to adult takes
about 18-35 days, depending on temperature. Viggiani (27), during
investigations on O. gonoceri Viggiani which is the parasitoid of Gonocerus
acuteangulatus Goeze, showed thta the preimmaginal development takes place in 8-12 days at 23-26°C
and at 50-70% of R.H. Maple (10) has also reviewed the biology of O. johnsoni
Howard on Murgantia histrionica Hahn eggs. Based on his results, the development of immatures is approximately 17
days. Masutti (11) reported that in O. pityocampae on Thaumetopoea
pityocampa Denis & Schiffermuller eggs the development from egg to adult takes
about 22-25 days. These apparent contrasting results could be due to using
different hosts. Our results showed that short development
period of O. pityocampae on B. signatum eggs can be an important
feature for mass rearing in the biological control of the pest.
4.2. Longevity of O.
The longevity of wasps fed with
honey and water and just honey was significantly higher than water-fed wasps
for both males and females (p < 0.001), which shows that honey, due to having having sugars such as Sucrose, Glucose, Fructose, and vitamins, plays a role in increasing longevity toward water (15). The longevity of Ooencyrtus was influenced by temperature and feeding regime. Rahim et al. (20) reported that in O. manii longevity of both sexes decreases with an increase in temperature; males live 4 to 1.2 days at temperatures of 15-36°C whilst females live from 10-1.7 days at the same temperatures. The lower longevity we observed in female wasps exposed to the honey and B. signatum egg in comparison with that observed for those fed with honey (Table 1) could be due to a less favorable feeding regime and/or the occurrence of oviposition activity. These results emphasize the importance of providing food sources to the adult wasps through habitat management (e.g. flowering plants) to enhance conservation or augmentation of biological control. 4.3. Parasitism percentage of O. pityocampae Egg-laying period, number of eggs, and longevity of egg parasitoids of in vitro depend on many factors, including temperature and relative humidity. According to many researchers, a change in temperature and relative humidity can also change longevity, egg-laying period, and number of eggs laid by wasps (28). In addition, in the different generations of the egg-laying period, number of eggs and longevity is changed. Also, the nature of the substrate at the oviposition site may affect rates of parasitism. For instance, in O. kuvanae, the eggs of the host on red maple (smooth bark) have a higher rate of parasitism than those on oak (rough bark) (3). Aung et al. (1) stated that the reproductive potential of 4–day–old females of O. nezarae is higher than 20–day–old and 1–day–old females. Also, Rajapakse et al. (21) stated that the optimum age of Cotesia marginiventris for successful parasitism of Spodoptera frugiperda ranged from 48 h to 96 h (21) and that C. marginiventris which were younger or older than the above age class were not able to parasitize a host. The results of the present study are consistent with the results of this researcher. 4.4. Sex ratio of O. pityocampae Sex ratio may be influenced by several factors including temperature, seasonal fluctuations, and microorganisms like Wolbachia. For example, in O. fecundus, all progeny are female if the ovipositing female is subjected to temperatures of 30°C, but all progeny are male if the ovipositing female is subjected to a temperature of 35°C (9). Battisti et al. (2) reported that males are very rare in natural populations (0.033%), whereas Tiberi et al (23) observed male emergence under laboratory conditions only when temperature at oviposition exceeded 30°C. Sex ratio of O. pityocampae parasitoid on the different eggs of host showed that females start egg-laying sequences by laying male eggs early in an oviposition bout in accordance with the males Ist strategy. These results suggest that changes in the sex ratio in each batch depend on the number of host eggs. According to the predictions of the local mate competition model, a decrease in the number of hosts offered to the females should result in an increased proportion of male eggs laid (22). When parasitoid wasps lay eggs in a patch, unfertilized eggs may be laid during the early duration of oviposition (5, 8). Such a 'male-first strategy' facilitates the production of optimal sex ratios by female parasitoids. If multi foundresses oviposit in a patch, there may be a reduction in clutch size per foundress because of limited oviposition sites in the patch. Higher proportion of male offspring means higher fitness to foundresses, because male offspring have the potential to mate with the female offspring of the other foundresses, and the value of males increases (6, 7, 30). Therefore, laying more unfertilized eggs at the beginning of oviposition should also bring a potential benefit to foundresses. When mating takes place in small patches and involves mostly relatives, theories predict that females are selected to maximize their fitness by producing few males, just the number necessary to guarantee that all their daughters will be inseminated, and a female biased sex ratio will also bring less local mate competition (LMC) among the sibling male offspring (6, 7, 30). But reduction of males also increase the probability of virginity in offspring. Foundresses may reduce the risk by ensuring sufficient male offspring. In addition, in parasitic Hymenoptera, mated females store sperm in the spermatheca and can manipulate offspring sex ratio (males/total offspring) by controlling fertilization during oviposition. The haplodiploid sex-determination system provides the mothers with a mechanism to control progeny sex ratio, because males develop from unfertilized eggs (haploid) and females from fertilized eggs (diploid) (5, 29). Tracy and Nechols (25) also reported that in O. anasae the proportion of females increases with the number of hosts parasitized. 5. Conclusions According to the results of the present study, it seems that this parasitoid can be expressed as a good candidate for mass rearing and releasing in nature, because the development time is rather short, and the proportion of high female has appropriate rate parasitism, and longtime longevity such as single characteristics in terms of considered characteristics have appropriate species for rearing and releasing clump for probability doing besides easy rearing. The obtained results in this paper reported ease in mass rearing on this parasitoid and effective control of pistachio green stink bug.