Black bean aphid, Aphis fabae (Homoptera; Aphididae) is a serious pest causing crop loss. Plant-aphid interaction is a dynamic system subjected to continual variation and changes. Host plants induce various biochemical and physical defense mechanisms due to aphid feeding. Aphids can overcome plant defenses by enzymatic adaptations and sequestering secondary metabolites produced by the plant within their bodies as a defense against their enemies. Many strategies were developed and evolved by aphids in order to overcome plant defense barriers which allowed them to feed, grow and reproduce on their host plants. This study aimed to aid in better understanding of the effect of altering host plant on specialist and generalist aphid fitness.The influence of plant defense on population development of Aphis fabae was also investigated. Analyses for insect enzymes were also demonstrated in addition to further biochemical studies on host plant defences. Generalists showed different ecological and enzymatic adaptations towards host plants than specialist Aphis fabae. The results were fully discussed in details.

Cotton leaf worm, Spodoptera littoralis, is considered one of the most common arthropod pests that contribute to crop devastation of cotton. Previously, agricultural pests were controlled through the application of chemical insecticides. However, insecticide-resistant insect populations emergence, as well as increasing concerns about the environmental and human health risks. Venomous animals introduce valuable sources of bioactive compounds which are employed for defence. Some of these toxins have high phyletic specificity, making them appropriate for use in IPM programs. This study aims to test the insecticidal effects of Polistes dominulus and Apis mellifera venoms. Crude venoms were examined for their insecticidal effect against cotton leaf worms by four different application methods including: leaf dipping, integument dropping, spraying, and injection. The data demonstrated a strong response to purified (Polistes dominulus) venom at an initial time than that of honey bee (Apis mellifera) which increases response with increasing the dose and the time interval. A dosage of 0.015 -0.16 ml of both venoms had notably varied in LD 50 values on Spodoptera littoralis that showed higher wasp venom toxicity. Cotton leaf worms showed more susceptibility and mortality to the Polistes sp. venom than that of honey bees.