A Comparison of the Effect of Some Ecological Parameters on the Occurrence of the Cotton Aphid, Aphis gossypii (Glov.) and Their Common Predators of Family Coccinellidae, on the Guava Trees in Qalubia Governorate, with Performing an Applied Biological Pest Control Experiment.

The present study was made in a guava orchard (variety Baladi) during the two successive seasons, 2018 and 2019, in Sariqous district (Qalubia Governorate). It was proposed mainly to compare the effect of seven different ecological parameters concerning the population density of the cotton aphid Aphis gossypii infesting the guava trees and also to record the common observed predatory coccinellids (in relation to the presence of these seven parameters). These parameters were: the position of the trees found in the guava orchard (a- the trees were in the borders of the orchard & b- the trees were inside the orchard); the levels of the tree leaves in the guava orchard (a- the leaves were located in the top of the tree, b- the leaves were located in the middle of the tree & c- the leaves were located in the trunk of the tree). Finally, the condition of the leaves located in the guava orchard (a- the old leaves found on the trees & b- the new leaves found on the trees). Obtained results indicated that, the cotton aphid A. gossypii had the highest critical periods of infestation of the trees, in April, 2018 & 2019 (in case of the trees that were in the borders of the orchard) and during May, 2018 & June, 2019 (in case of the trees that were inside the orchard). The mean total numbers of aphid' individuals (winged adults & wingless individuals) were found to be lower on the trees that were located in the borders of the guava orchard (695.25 (0-4666)) than those located inside the orchard (912.60 (0-5071)). The pest had also highly critical periods of infestation of the trees, in May 2018 and 2019 (for the leaves that were in the top of the tree & in case of the leaves that were in the middle of the tree), but was during May, 2018 & June, 2019 for the leaves that were in the trunk of the tree. The aphid infestation was the highest on the leaves located on the middle (1014.85 (0-7814)) of the tree, in comparing with those leaves located either on the top (656.60 (0-4654)) or on the trunk of the tree (559.30 (0-3134)), respectively. Besides, the pest had very low periods of infestation of the trees for the old leaves found on the trees, while the highly critical period was during April, 2018 & May 2019 in case of the new leaves found on the trees. The aphid infestation on the new leaves was greatly higher than those recorded on the old ones in seasons, 2018 and 2019. Generally, it could be concluded that the three successive months; April, May, and June had the highest months of aphid infestation on the guava trees during the present study. Four predators of family Coccinellidae were recorded in relation to the occurrence of the cotton aphid A. gossypii including: Coccinella undecimpunctata L., Hippodamia convergens (Geur.), Cydonia vicina nilotica and Cydonia vicina isis. The sequence of the common recorded four predatory coccinellids adults for the two seasons together on the guava trees were as follows: H. convergens (the mean was 49%) > C. vicina isis (22%) > C. undecimpunctata (19%) > C. vicina nilotica (10%), i.e.,the occurrence of the predator H. convergens was the highest in comparing with the other recorded predators. For this reason, a biological control experiment was performed by laboratory mass-rearing and releasing the predator H. convergens adults (pairs of males & females), for controlling the cotton aphid A. gossypii on the guava trees during season, 2019 (in a guava orchard near the orchard used in comparing the seven parameters). The percentages of reduction in the experimental area (in which the predator H. convergens were released) were; 17.19%, 53.98%, 73.85%, 76.26%, 72.65% and 55.16% in comparing with the control area (in which the predator H. convergens was not released at all) in case of the following features: the mean of infested trees/10 trees, the mean of infested leaves/500 leaves, the mean number of cotton aphid A. gossypii/one guava leaf, the total number individuals of winged aphid adults, the total number of wingless aphid individuals and the total number of the aphid species/season 2019, respectively. So, the predator H. convergens is a useful biocontrol agent for the cotton aphid A. gossypii and could be laboratory mass-reared and field released on a large scale against the pest on the guava trees or other fruit trees, side by side with other available safe control methods in the frame of Integrated Pest Management (I.P.M.) programs, for protecting man heath and the surrounding environment from pollution