The Effect of Planting Dates and Nitrogen Fertilizer on Aphis craccivora (koch) Infestation in Faba Bean (Vicia faba, L.) fields

The present study was carried out at Wadi El Natrun district, El-Behera Governorate during season 2019–2020. In a field study, the effect of two planting dates and three rates of nitrogen fertilizer on a population of Legume aphid, Aphis craccivora (Koch) (Homoptera: Aphididae), in faba bean (Vicia faba, L.)were investigated. The results show that the higher occurrence of the aphid was recorded on the early planting date than the recommended one. The combination effect of climatic factors and plant age on aphid population density was presented as explained variance which was 75 and 74% in the early and recommended planting dates respectively. The population densities of aphid were significantly lower on faba bean plants fertilized with the lowest rate of nitrogen fertilizer (75 kg feddan−1), compared with those fertilized with recommended and highest rate (100 and 125 kg feddan−1 respectively) in both early and recommended planting dates. These results indicate that the recommended planting date and moderately plant nutrition can help plants to avoid insect pests infestation.


INTRODUCTION
In developing countries, faba bean is used as human and animal food, while in rich countries they are used as animal food. In Egypt, faba bean is one of the most important leguminous crops, as it is used as vegetables, dried, or eaten green (Mohamed 2003). Faba bean is known as a meat substitute (Ebadah et al., 2006). In addition, faba bean has the ancillary benefits of nitrogen fixation in plants and thus reduce fertilizer requirement (Hendawey and Younes 2013). In the field, faba bean crop is liable to infestation by many insect pests, in the worldwide aphids are the most dangerous insect pests on crops, it is cause damage either by direct feeding by sucking plant sap or by the transmission of plant viruses and honeydew (Pickett et al., 1992).
Legume aphid, Aphis craccivora (Koch). (Homoptera: Aphididae) species is widely distributed in different habitats in the world. Aphids are among the most dangerous insect pests that affect crops in Egypt (El-Defrawi et al. 2000). Planting date is an important factor for crop production as well as aphid infestation level. The population density of A. craccivora was significantly affected by the planting date (Hassanein 1994).
In host plant-herbivore interactions, nutritional plant quality plays an important 2 role. The fertilizers are sources of mineral elements that the plants required for growth and development (Chau et al. 2005). Nitrogen is the most critical macronutrient, which deeply affects the development and fertility of herbivorous insects. Improving the nutritional quality of plant tissues by high nitrogen fertilization increases plants Sensitivity to the infestation of herbivorous insects attributed to their population growth (Fallahpour et al. 2015). Agricultural control as planting dates and soil fertilizer management is important alternative pest management as compared to chemical control. The soil fertilizer application as a part of cultural control can impact the physiological susceptibility of plants to insect pests by either affecting the resistance of plants to infestation or by altering plant acceptability to certain insect pests (Letourneau and Goldstein, 2001). Because the farmers' lack of commitment to planting dates and the recommended fertilization rates, which have an impact on the levels of insect pests infestation on the crops, therefore, this research aims to evaluate the effect of two planting dates and three rates of nitrogen fertilizer on the aphid population density on faba bean in the field to avoid this injurious pest infestation and reduce the application of chemical pesticides.

Experimental Area and Design:
The present study was carried out at Wadi El Natrun district, El-Behera Governorate during season 2019-2020 on the Spanish variety faba bean (Vicia faba L.). The experiment was carried out in a completely randomized design with three replicates (each replicate 42 m 2 ) with two factors, i.e. planting dates; early (20 October) and recommended (5 November) and nitrogen treatments. All agricultural operations were carried out according to recommendations in all treatments without applying insecticides.

Nitrogen Treatment:
Three rates of nitrogen fertilization were 75, 100 (as the recommended rate of nitrogen feddan -1 ) and 125 kg feddan -1 were added in two batches. The first batch was added with the first irrigation of the crop and the second batch two weeks after the first application. Nitrogen fertilizers had been added to the soil in the form of ammonium sulfate.The aphid samples were taken by direct counting on plants in the field and their numbers were recorded on five randomly selected plants in each replicate from the start of the infestation. Data were recorded weekly from early November till the end of March. The climatic factors such as daily maximum & minimum temperatures ( 0 C) and R.H. (%) recorded during the above studied period were obtained from Central Laboratory for Agricultural Climate, Dokki, Giza, one week earlier from the insect inspection.

Statistical Analysis:
The obtained results of planting date and nitrogen fertilizer were subjected to analysis of variance (ANOVA). Means were determined for significance using Duncan test in SAS (Anonymous 2003). The data of abiotic factors were analyzed using Procedure Correlation and Regression in SAS (Anonymous. 2003). Aphid data were homogenized using running means ((a+b+c)/3) for reducing sampling errors. Weather factors (i.e. max & min. temperatures ( 0 C), and RH (%) were considered as linear ones). Data were fitted to the polynomial model, where plant age (as weeks) was presented as the third degree of polynomial (i.e. Age, Age 2 and Age 3 ). The multiple polynomial equations become Y= a ± b1 T. max. ± b2 T. min. ± b3 RH ± b6 Age ± b7 Age 2 ± b8 Age 3 .

Effect of Planting Date on the Population Density of Aphis craccivora:
The results in Fig. (1) show the population density of A. craccivora on faba bean in the early and recommended planting dates during season 2019-2020. The higher occurrence of the aphid was significantly (P=0.0001) recorded on an early planting date with an average of 35 aphid plants -1 than the recommended planting date with an average of 18 aphid plants -1 . Aphid began to appear immediately after the emergence of the seedlings in both planting dates. Then, the numbers increased until they reached their peak during the first half of December with an average of 89 and 54 aphid plants -1 for early and recommended planting date respectively, when the average maximum temperature in this period was about 22 0 C (Fig. 2). After that, the population gradually decreased until it reached the lowest population (16 and 7 aphid plant -1 for early and recommended planting date, respectively) in late January and early February when the average of max. temp. reached 17 0 C (Fig. 2). The population reincreases until the end of the season with increasing the temperature. These results are consistent with those obtained by Mahmoud et al. (2015) who recorded that A. craccivora reached the peak at the end of Nov. to half of Dec. on faba bean plants at El-Menofeyia governorate, Egypt). Abd El-Rahman (2003) recorded one peak for A. craccivora on faba bean in the 3 rd week of Dec. Saeed and Razaq (2014) and Nisar & Rizvi (2017) found that the different planting dates had a significant effect on the aphid population. Seiter et al. (2019) stated that the planting date affects the aphid density, and this is an effective tactic to reduce aphids damage to the crops. In determining insect population dynamics on a host plant, ambient temperature, natural enemies of insects and host plant status are key factors (Cisneros and Godfrey, 2001).

Factors Affecting the Population Density of Aphis craccivora on Vicia faba:
In general, population changes are caused by changes that occur either in weather conditions or in the abundance of food supply as well as in the number of natural enemies. These abiotic and biotic factors normally affecting the biotic potential of insect pests; reproduction and survival potential. The obtained results indicated that a few numbers of natural enemies namely: Coccinella undecim punctate, Hipodamia varigata and Syrphus corolaae were associated with the aphid samples on the faba bean crop. The combined effect of climatic factors (daily mean of max. & min. temp. and daily mean of percent relative humidity) and plant age on the population density of A. craccivora on Vicia faba plant in two planting dates during 2019-2020 at El-Behera Governorate ( Table 1). As shown in Table (1) the effect of all previous factors in simple correlation had an insignificant effect (P> 0.05) on the aphid population during the early and recommended planting date. The exact relation between the studied factors and aphid population density was determined by estimating the partial regression values. The results show that all values of climatic factors were insignificant (P> 0.05), while plant age values were significant (P<0.01) during both early and recommended planting dates. The effect of the combination of all studied factors on aphid population was presented as explained variance (EV%) which was 75 and 74% in early and recommended planting dates respectively (Table 1). The present results are close to that mentioned by Mahmoud et al. (2015) who show that both the climatic factors and plant age vary in their effect on A. craccivora population, where the correlation between weather factors, plant age and the insect population density was insignificant. Also, they recorded that the combined effect of the ecological factors on aphid population in season 2011-2012 was 98.98 and 50.42% in season 2012-2013 in El-Menofeyia Governorate. Salman et al. (2015) who mentioned that population fluctuations of A. craccivora on faba bean are probably due to climatic condition in Aswan Governorate.

Effect of Nitrogen Fertilizers on Population Densities of A. craccivora:
The results in Figures (3 A & B) indicated that A. craccivora population densities varied significantly among the soil nitrogen fertilizer treatments in both early (LSD5% = 15.07, P = 0.008) and recommended planting dates (LSD5% = 9.56, P = 0.009).
The population densities of aphid were significantly lower on faba bean plants fertilized with the lowest rate of nitrogen fertilizer (75 kg feddan −1 ), compared with those fertilized with recommended and highest rates (100 and 125 kg feddan −1 respectively) in both early and recommended planting dates. The mean numbers of aphid were 28 & 19 aphid plant -1 with 75 kg per feddan nitrogen fertilizer and they were 40 & 24 aphid plant -1 with 100 kg per feddan nitrogen fertilizer, while treatment with the highest rate of nitrogen fertilizer (125 kg per feddan) lead to increase aphid numbers to 52 & 34 aphid plant -1 in early and recommended planting dates respectively (Fig. 4). Similar results have been reported by Salman et al. (2007) who mentioned that the population density of aphid significantly increased with the increase of N fertilizer levels. Hosseini et al. (2014); Sinha et al. (2018) and Fallahpour et al. (2020) who stated that the population of aphid was positively affected by nitrogen fertilization; the highest abundance was recorded in plants growing with the highest rate of nitrogen fertilization. Which could explain the higher number of the aphid on plants fertilized with a higher nitrogen rate. This effect could be achieved directly through changed plant physiology and the composition of plant metabolites and indirectly by a change in plant defense mechanism and decrease regulation of defense pathways (Fallahpour et al. 2015). The effect of nitrogen fertilization on plant nitrogen content may have important consequences on nutrition, growth rate, fecundity (Douglas 1993) and the numbers of herbivorous insects (Awmack and Leather 2002;Blazhevski et al. 2018).

CONCLUSIONS
The obtained results indicated that the recommended planting date (5 Nov.) had significantly lower numbers of Aphis craccivora on faba bean comparing with the early planting date (20 Oct.). The population density of A craccivora on faba bean was increased significantly with increasing soil nitrogen fertilization rate. So, sowing the plants during the recommended planting date and moderately plant nutrition can help plants to avoid insect pests infestation and reduce the application of chemical pesticides.