ی. فتحی پور

Among several pests infesting okra plants, the cotton mealybug, Phenacoccus solenopsis (Hemiptera: Pseudococcidae) is considered one of the most destructive pests. Field trials were conducted in a private field in Esna District, Luxor Governorate, Egypt, during two successive growing seasons (2021 and 2022) with the aim to study the seasonal fluctuation of P. solenopsis population infesting okra plants (Balady cultivar). Furthermore, the impacts of both climatic conditions and plant age on the seasonal variation of the tested insect pest were determined. The results indicated that P. solenopsis infested okra plants from the first week of March until the end of July, and had three peaks of activity per season, which were recorded in the first week of April, third week of May, and fourth week of June. The mean total population density of P. solenopsis per 10 leaves over the whole first season was 235.96±16.05 individuals and for the second season, it was 242.13±17.01 individuals. June was the most favourable month for P. solenopsis population increase (as measured during weekly inspections), while March was the least favorable in both growing seasons. Pooled effects of environmental conditions and plant ages had a strong relationship with P. solenopsis population density, with an Explained Variance (EV) of 93.26% in the first season and 95.09% in the second season, during the two seasons. Daily mean relative humidity was the most effective variable in explaining changes in the population density of P. solenopsis for the 1st season (2021), while the it was the major element influencing the changes in population in the 2nd season. On the other hand, the daily maximum temperature was clearly the least effective factor in population changes during both seasons. The data presented here can aid to monitor the oscillations in the population density of this pest.

Demographic parameters of the parasitoid wasp Trichogramma embryophagum Hartig reared on Sitotroga cerealella (Olivier) were determined for 40 generations (G5-G40). The experiments were done in a growth chamber at 26±2°C, 65±5% RH and photoperiod of 16:8 h (L:D). The results showed that the female longevity decreased significantly during successive production, ranging from 10.68 (in G5) to 9.64 days (in G40). On the other hand, the male longevity decreased significantly in the 20th generation and no significant difference was found from G20 to G40. The oviposition days and mean total fecundity of T. embryophagum decreased as the number of generations increased. Generally, the wasps in earlier generations had longer adult longevity, longer life span, and higher fecundity than later generations. Moreover, sex ratio of T. embryophagum was not significantly different in successive generations. Results of paired bootstrap test indicated that all population growth parameters of T. embryophagum reared on S. cereallela were significantly different in successive generations. The highest and lowest values of the intrinsic rate of increase (r), finite rate of increase (λ), net Reproductive rate (R0), Gross Reproductive Rate (GRR) and mean generation Time (T) of T. embryophagum were observed in G40 and G5, respectively. These results suggest that T. embryophagum wasps reared in sequential generations can be used successfully in biological control programs until the 20th generation without any loss of quality or performance; after that, regular rejuvenation of laboratory population by occasional importing of field-collected parasitoids should be done.

Population density and dispersion pattern of Sesamia cretica Led. was determined in maize fields in Varamin (Ahmadabad and Khaveh) and Rey (Aminabad and Talebabad) areas (Tehran, Iran) during two agricultural seasons, 2017 and 2018. A whole plant of maize was selected as a sampling unit to estimate the number of S. cretica larvae. The highest population density of S. cretica larvae per plant was recorded on the 4th and 8th October in Aminabad, 17th and 20th September in Talebabad, 6th and 17th September in Ahmadabad and Khaveh, in 2017 and 2018, respectively. Mean densities of the larvae per plant were 52.62±12.53, 10.50±2.85, 17.45±3.48, 7.57±1.55 in 2017 and 12.00±5.29, 1.00±0.30, 11.05±2.36, 12.00±3.41 in 2018 in Aminabad, Talebabad, Ahmadabad, and Khaveh, respectively. The population of captured male adults in all fields in the second year was less than the first one. Peak numbers of male moths had a difference of 10-22 days between the two studied years. Based on the index of dispersion, the spatial distribution of S. cretica larvae in all fields in both areas was aggregated during the two years of study, except for Aminabad in 2018. According to Taylor’s power law, S. cretica in Ahmadabad and Aminabad in 2017 had a random pattern, while in all fields of the other regions it had an aggregated spatial distribution during 2017 and 2018. In Iwaochr('39')s model, the regression between the mean crowding and the density was not significant in Aminabad and Khaveh in 2017 and Talebabad in 2018, while in the other fields indicated the aggregated spatial distribution. The lowest estimate of the sample size was computed by using Taylor’s power law. The results revealed that population fluctuation of S. cretica was affected by the region, but in spatial distribution pattern, the oviposition behavior of the pest was a much more determining factor than the region. The coefficients of the spatial pattern can be used for improving the sampling program to calculate the population density of S. cretica precisely.

The nutritional indices are an important tool in evaluating herbivore responses to variation in host nutritive properties. The current study was conducted to unveil the effects of ten canola cultivars (Brassica napus L.) (chr('39')Operachr('39'), chr('39')Licordchr('39'), chr('39')Okapichr('39'), chr('39')Talayechr('39'), chr('39')Zarfamchr('39'), chr('39')Modenachr('39'), chr('39')SLM046chr('39'), chr('39')Sarigolchr('39'), chr('39')RGS003chr('39') and chr('39')Hayula420chr('39')) on consumption and utilization indices of the Spodoptera exigua (Hübner) larvae. The results revealed significant differences in nutritional indices of different larval instars of S. exigua fed on the mentioned canola cultivars. The highest value of Digestion Ability of food (AD) for the third and fourth instars was observed on Licord (86.57% and 83.08%, respectively), and for the fifth instars was on Opera (68.79%). The Relative Growth Rate (RGR) and Relative Consumption Rate (RCR) in the fifth instar larvae were significantly greater on Opera, Okapi and Talaye, whereas the lowest values of Conversion Efficiencies (ECI and ECD) were recorded on these cultivars. The highest ECI was observed in the larvae that consumed RGS003 (24.27%), Hayula420 (20.36%), and Sarigol (19.17%). Furthermore, the larvae reared on Okapi exhibited the highest RGR, which confirms high susceptibility of this cultivar. Based on the obtained results, Okapi, Talaye and Opera were the cultivars susceptible to S. exigua.

Augmentative release of native natural enemies is a prominent strategy for suppression of crop pests. Intrinsic differences among populations of natural enemies may affect their efficiency in pest management programs. We characterized life history traits of 13 climatically and geographically isolated populations of Habrobracon hebetor Say (Hymenoptera: Braconidae) from different regions of Iran to assess their suitability for biological control of noctuid moths. All experiments were performed at 25±1°C, 65±5 RH and 16:8 (L:D) hours photoperiod regime. Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae) was used as a laboratory host. Our results revealed significant variation in female longevity, paralysis and parasitism rate, sex ratio, reproductive rate and host allocation among different H. hebetor populations tested. The highest number of offspring (124.2) and parasitized larvae (160.1) were observed in Bandar Lengeh and the lowest ones was observed in Urmia and Jiroft, respectively (3.4 and 9.3 for Urmia and 3.1 and 10.1 for Jiroft). Also, the wasps of Bandar Lengeh paralyzed more than 95% of the introduced host larvae. The longest female longevity and male production (21.3 days and 80.1, respectively) were in Bandar Abbas and Bandar Lengeh (21.3 days and 80, respectively), while the lowest ones were in Dehloran (12.9 days and 40.2, respectively). Gorgan population deployed the highest number of Ephestia kuehniella larvae in foraging behavior test. These results show considerable variation in the life history traits of various populations of H. hebetor, which may affect performance of these populations under field condition.

The effects of different fertilizers including ‘Cow manure’, ‘Vermicompost’, ‘NPK’ (20-20-20 NPK), ‘NPKBN’ (NPK̺ⶡ뚜뗪 vinelandii), ‘NPKBP’ (NPK㶩 agglomerans㻇깶覨鶫 putida), and ‘NPKBNBP’ (NPK̺ⶡ뚜뗪 vinelandii㶩 agglomerans㻇깶覨鶫 putida) were compared with the control treatment. Comparisons included not only the nutrient and chlorophyll content of cucumber leaves, but also the demographic parameters and body size of Aphis gossypii Glover. The highest nitrogen content (2.45%) was observed in ‘NPKBN’ and the highest phosphorus, along with potassium content (0.58 and 12.17%, respectively) was observed in ‘cow manure’ treatment. The highest chlorophyll content (37.51 SPAD units) was measured in ‘NPKBNBP’ treatment. Results showed that the intrinsic rate of increase (r) varied from 0.409 (in ‘Cow manure’) to 0.480 d-1 (in ‘NPKBP’) under application of different fertilizers. Net Reproductive rate (R0) varied from 71.65 to 79.25 nymphs/individual in ‘Vermicompost’ and ‘NPKBP’ treatments, respectively. The largest (1.28 mm) and smallest (1.00 mm) body length of the aphids was measured on ‘Vermicompost’ and ‘Control’, respectively. Results revealed that ‘NPKBP’ was the most suitable fertilizer for population growth of A. gossypii, compared with the other treatments, and the aphid’s longevity and fecundity was relatively low under ‘Vermicompost’ application.