الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Cucurbits are one of the most widely grown vegetable crops in the world, and they are a vital element of a healthy diet. In Egypt, squash, Cucurbita pepo, L., is one of the most popular vegetable crops, which consumed in different ways as food. Aphids, particularly Aphis gossypii Glov. is one of the most important pests in squash farms, causing serious damage by sucking plant sap in addition to plant viruses transmission such as Papaya ringspot virus-W (PRSV-W). Therefore, this work was carried out at the private farm at Kafr El-Sheikh governorate (during fall of 2019 and 2020) and laboratory of piercing-sucking insects at Sakha Research Station to study: 1- efficacy of three insecticides (imidaclopride, pymetrozine and flonicamid) and mineral oil (KZ-oil) against Aphis gossypii Glov., the associated common predators and the incidence of PRSV as well as its relation to the components of squash yield under field conditions, 2- the relationship between aphid population, incidence of PRSV and fruit yield, 3- evaluation the effects of three aphidophagous predators: chrysoperla carnea (Stephens), Adalia bipunctata (L.) and Syrphus sp., on the spread of A. gossypii and PRSV in a squash crop under greenhouse conditions, and 4- effects of PRSV infection in squash on the biology of its vector; A. gossypii along with virus-free plants. The obtained results could be summarized as follows: A- field experiments: - 1. Effect of certain insecticides and mineral oil against aphids and associated predators on squash plants: The results of the two seasons, indicated that imidacloprid (20SC) was the most effective compound in suppression of aphid, A. gossypii population on squash, followed by flonicamid (40 WG) and pymetrozine (50 WG), while the KZ oil (95%EC) significantly was the least effective one. With regard to the common natural enemies existed in squash fields, three main predatory insects: Syrphids, coccinellids and chrysopids in addition to spiders were counted. The first species was the most dominant. Kz oil and flonicamid were more safe to the existed predators, while imidacloprid was the most harmful to the predators. 2. Effect of certain insecticides and mineral oil on incidence of papaya ringspot virus in squash plants: The results cleared that the incidence of PRS virus was clear on squash plants in the second season than in the first one. This might be due to the higher number of aphid population in the second season than in the first one. The infected plants by virus increased over time, with the control being the highest in most cases. KZ oil significantly was the most effective in reducing PRS virus spread, while imidacloprid (20SC) was the least effective in reducing PRSV spread. Flonicamid (40 WG) and pymetrozine (50 WG) induced relatively moderate effect. 3. Effect of certain insecticides and mineral oil on the plant size and fruit yield of squash plants The results indicated that KZ oil induced maximum height and width of plants as well as high remarkable yield fruit followed closely by flonicamid and pymetrozine. Also, the plants treated with mineral oil recorded maximum yield of squash fruits followed by flonicamid and pymetrozine. 4. Relationship between aphid population, incidence of PRSV and fruit yield of squash The high yield was correlated with the least virus infection and vice versa. Control treatment that had high virus infection recorded the least yield. On the other hand, imidacloprid that had less effect on virus infection induced low yield. The aphid population was positively correlated with incidence of PRS virus. Fruit yield was also negatively correlated with incidence of PRS virus and aphid population. B- Laboratory experiments: - 1- Effects of certain insecticides and KZ oil on Aphis gossypii and its transmission of papaya ringspot virus (PRSV) on squash The obtained results revealed that flonicamid and pymetrozine significantly reduced virus acquisition and inoculation compared to the untreated control, and the reduction was comparable to a mineral oil application. Also, results of the residual activity of insecticides and KZ oil on PRSV transmission rate by A. gossypi revealed that flonicamid had significantly higher persistence up to 12 days, as the transmission rate of virus was 30% followed by pymetrozine with 35% transmission compared to KZ oil (70%) and control (80 % transmission rate). The mineral oil experienced a significant increase in transmission rate as its efficacy decreased dramatically on the eighth (45 % transmission) and twelfth days (70 %). 2- Effect of PRSV-infected squash plants on biology and life table parameters of Aphis gossypii Glov.: - Statistical analysis of data revealed that the adult fecundity significantly increased when aphid, A.gossypii fed on virus-infected plants (53.22 nymphs/female) compared to those fed on non-infected plants (39.82 nymphs/female). Also, feeding aphids on virus-noninfected plants prolonged the time of nymphs development than on infected ones. On contrast, the adult longevity was longer on virus infected plants than on non-infected ones, but without significant difference. The effect of PRSV-infected squash plants on A. gossypii life table parameters revealed that the net reproductive rate (Ro) of adult apterae, the intrinsic rate of increase (rm), the finite rate of increase (λ) and the growth reproduction rate (GRR) were significantly higher on infected plants than non-infected plants. Furthermore, the mean generation time (T) of aphids fed on non-infected plants was longer than on infected ones. Also, doubling time (DT) was significantly higher on non-infected plants compared to infected ones. 3- The effect of certain predators on the spread of Papaya ringspot virus (PRSV) by Aphis gossypii Glov. The effects of three predators ; chrysoperla carnea (Stephens), Adalia bipunctata (Linnaeus), and Syrphus sp. on the dispersal of the aphid vector A. gossypii and PRSV transmission rate revealed that initially (after 1 day), C. carnea and A. bipunctata, statistically increased aphid colonization on nearby plants than Syrphus sp., thus the transmission rate of virus was greater in the presence of C. carnea , A. bipunctata than Syrphus sp. In contrast, after 7 days, the virus transmission increased somewhat, but without significant difference between the treatments.