The Egyptian alfalfa weevil (EAW), Hypera brunneipennis (Boheman) (Col.: Curculionidae), is considered one of the most damaging economic insect pests attacking the Egyptian clover, Trifolium alexandrinum L., and alfalfa, Medicago sativa L., in Egypt. Population abundance of EAW in clover fields of Egypt was reported by different authors, and it was present all over the season beginning from December to May (El Sherif et al. 1978; El-Mezayyen 2001; El-Mezayyen 2003; Rakha 2008, and Awadalla et al. 2014). The larvae and adults of the weevil are feeding on the foliage of alfalfa and clover, but the larvae cause more damage. They prefer to feed on the young leaves. Adults generally feed on the leaf margins (Rakha 2008; Baysal et al. 2018). The young larval instars feed on the plant terminals, and the older ones feed on the leaflets. Under high infestation, the plants could completely be defoliated. Symptoms of infestation appear in winter/spring, especially in alfalfa and clover areas at field edges adjacent to eucalyptus and date palm trees (adult weevil aestivating sites). This pest is found in all alfalfa-producing areas worldwide (Cook et al. 2004; Atanasova 2012). Leguminous crops are its host plants (Summers et al. 1975; Al-Azawi et al. 1986; Fouad et al. 2012; Awadalla et al. 2014). The EAW generally has one generation per year in South Europe and North America. In recent years, it has evolved from a univoltine (one generation per year) into a multivoltine (several generations per year) insect. Rather than leaving the field for aestivation, some adults remain in the alfalfa, mate and continue to lay eggs. These eggs soon hatch, giving rise to a second generation of weevil larvae that continue to cause damage to the second and sometimes third cuttings (Cook et al. 2004).
As forage crop, alfalfa and clover fields in Egypt are not treated with chemical insecticides, except after seed germination, when plantlets were severely attacked by the cotton leaf worm, Spodoptera littoralis (Boisd.) before re-sowing the crop again. Generally, no control actions are needed to control the EAW in the Egyptian clover (T. alexandrinum) in Egypt because the farmers tolerate its damage in the crop among the season and avoid using insecticides on this important forage crop for their farm animals (EL-Husseini 1981). Also, the weevil larvae present on the plants are removed by the first and the next successive cuttings. In case of M. sativum that remains growing in the field for few successive years, the damage caused by EAW adults and larvae increases year after year, and sometimes, there are necessitates to control action (Cook et al. 2004).
In such an important forage crop for farm animals with no use of chemical insecticides, the biological control is the alternative for controlling its insect pests, especially the microbial control with entomopathogenic viruses, bacteria and fungi. The use of entomopathogenic fungi (EPF) in biological control of insect pests has become of immense significance due to their environmental and food safety concerns (Reddy et al. 2016; Mascarin and Jaronski 2016). Species of the genera Beauveria, Metarhizium, Lecanicillium and Isaria are commercially produced (Vega et al. 2009). B. bassiana was reported to infect 707 species of insect hosts, including 521 genera and 149 families of 15 insect orders (Imoulan et al. 2017). B. bassiana was successfully applied against various insect pests worldwide, e.g., Bemesia tabaci (Mascarin et al. 2013), Nilaparvata lugens (Rombach et al. 1986) and Anoplophora glabripennis (Dubois et al. 2004). B. bassiana was previously isolated from aestivating dead H. brunneipennis in Egypt (El-Sufty et al. 1993). It is believed that the key period for managing the alfalfa weevil in Egypt, with bioinsecticides, especially the EPF, is in the late season before the last cutting in order to contaminate the adult weevils before leaving them to their aestivation sites under loose bark of the trees around the fields like eucalyptus and date palms. Under such shelters, the fungi developed on the contaminated adult weevils, infect and kill them, thus suppressing population of the active weevils in the next season.
Under the current scenario, the present study aimed to monitor larval and adult weevil population of H. brunneipennis before and after the application of the conidiospores of the fungus B. bassiana on alfalfa before the early summer cutting (April/May). The mortality of the adult weevil during their summer aestivation under the loose bark of the eucalyptus trees present around the treated field was monitored.