Effect of sowing dates on the populations of three major insect pests and associated natural enemies throughout the growth stages of maize plants

In Egypt, maize is an important crop that is attacked by various pests. In the present study, the effect of maize planting dates on the populations of insect pests and their natural enemies were investigated throughout the growth stages of maize plants. The maize planting dates were at the beginning of May, Jun, and July in the 2019 season and were repeated in the 2020 season. Samples were collected weekly to determine the populations of the insect pests, Limothrips cerealium (Haliday, 1836), Rhopalosiphum maidis (Fitch, 1856), and Sesamia cretica Lederer, 1857 and their natural predators. For the first sowing date, the infestation percentage of L. cerealium and S. cretica were most substantial, especially in the seedling and precorn formation stages. For the third sowing date, the number of R. maidis was most substantial, especially in the corn formation stage. Three predators were associated with these insect species; of these predators, Coccinella undecimpunctata (Linnaeus, 1758), Scymnus interruptus (Goeze, 1777), and Chrysoperla carnea (Stephens, 1836) were observed at the highest numbers during all sowing dates. A highly significant correlation existed between populations of S. interruptus and the three insects across the two seasons. Data suggest that the percentage of thrips, aphids, and stem borers infestations can be minimized by planting maize varieties in June.

Effect of silver and silica nanoparticles on the larvae of pink stem borer Sesamia cretica Lederer, 1857 (Lepidoptera: Noctuidae) and maize plants Zea mays Linneaus, 1753

This study was aimed to evaluate the toxicological and biological effects of three nanoparticles (silver, hydrophilic and hydrophobic silica) at four concentrations (100, 200, 400 and 800 ppm) against 1st instar larvae of Sesamia cretica Lederer, 1857 and its effects on some maize characters. Each concentration and control was repeated 4 times (10 larvae/replicate). Larvae were fed on treated stem maize and mortality rate was recorded. After treatment with LC50 values, the survival larvae were collected and the larval duration, pupal duration, pupal weight, pupation percentage and adult longevity were recorded. Seedling maize plants were sprayed with three concentrations (50, 100 and 200 ppm) at 4 categories (every 1, 3, 7 and 14 days) to detect the effect of nanoparticles on leaf area, extended height and leaf chlorophyll content. Results showed that hydrophilic silica nanoparticle was the most effective, followed by silver nanoparticle then hydrophobic silica nanoparticle with LC50 121.19, 405.71 and 416.82 ppm, respectively. All nanoparticles led to increase in larval durations, reduction of egg number per female and decrease of eggs hatchability rate. All nanoparticles caused positive effect on leaf area, extended height and chlorophyll content. These nanoparticles may be recommended to control S. cretica with positive effects on plant characters.

Sesamia cretica (greater sugarcane borer).

The geographical range of S. cretica includes most of the countries and islands of the Mediterranean basin and extends through the Middle East and Arabia to Pakistan, northern India and northern Africa, extending south to northern Kenya and northern Cameroon. According to Tams and Bowden (1953) this species does not extend westward of Cameroon; however, earlier records from Mali, Niger and Togo have again been included on the recently revised CABI/EPPO (2001) distribution map. This is a pest species linked to graminaceous crops with a preference for sorghum, maize and sugarcane. It is present on wild Gramineae with a preference for Panicum repens. S. cretica could extend its range following these crops/wild hosts and in correlation with climatic change. More studies on the distribution of this species are necessary. It belongs to the 'Sesamia' group of noctuids, a group of very similar species that are difficult to identify, and therefore misidentifications can occur regarding new distribution data.

Seasonal abundance of the most important insect pests of maize and their natural enemies in Egypt

The experiment was conducted to study the seasonal abundance of the most important insect pests of maize and its relation with natural enemies and weather factors in Assiut governorate during 2019 and 2020 seasons.The samples were examined from June to September to determine the population of Limothrips cerealium (Haliday, 1836), Rhopalosiphum maidis (Fitch, 1856) and Sesamia cretica Lederer, 1857 and its the associated predators. The population of L. cerealium recorded a peak in the 4th week of July 2019 and the 1st week of August 2020. The highest population of R. maidis occurred in 1st week of September at both seasons. The simple correlation and regression between L. cerealium population and three weather factors were insignificant in both seasons while S. cretica population were found to be significant with R.H%. The population of R. maidis in the 1st season was insignificant negative with temperatures but was significant in the 2nd season. The plant age was more effective than the weather factors on the population of the three insect pests. The common predators were Orius albidipennis (Reuter, 1884) and Scymnus interruptus (Goeze, 1777)which were highly significant with all three insect pests.

Meteorus gyrator (Thunberg) (Hymenoptera: Braconidae) In Egypt: Geographical Distribution and Mass-production

Background: The larval internal parasitoids in the genus Meteorus attack certain lepidopterous larvae in different Egyptian fields. Two species, M. rubens and M. gyrator were the most abundant species reared from several lepidopterous larval species, which feed on different host plants in the two selected Governorates in Egypt throughout two successive years. Aim: This work presents a method specifically designed to improve the abundance and the parasitizing potential of M. gyrator in open fields to parasitize and develop on a broad range of noctuid’s pests by releasing considerable number of the parasitoid adults. Also it deals with some aspects of the basic biology of M. gyrator parasitizing Spodoptera littoralis and Autugrapha ni, as mass-rearing hosts. Methodology: 1- Population Dynamics Biweekly samples of lepidopterous larvae were collected from different host plants in the fields of Giza and Faiyum Governorates, for two successive years (November, 2017 to October, 2019). Collected larvae were confined individually under constant conditions until pupation or the emergence of the internal parasitoid’s larvae for pupation. 2- Laboratory Rearing Cultures of some insect larvae, Heliothis armigera, Spodoptera exigua, Agrotis ipsilon, Sesamia cretica, S. littoralis and Autographa ni were reared in laboratory under constant conditions to act as hosts for mass-production of the parasitoid, M. gyrator. Results: Obtained results reveal that A. ipsilon was the main host of M. rubens, it was more abundant in both years and localities of the survey. Meteorus gyrator was recorded at fewer numbers; it was reared from S. littoralis, S. exigua, S. critica, Heliothis spp. and Autographa spp. The parasitism percentage by M. rubens averaged 23.10% at Giza. While in the case of M. gyrator it averaged 3.25%. In Faiyum, the corresponding figure averaged 12.96% parasitism for M. rubens; while it averaged 6.93%, for M. gyrator. To increase the efficacy of M. gyrator, mass production experiments were carried out, suggesting that Autographa ni was the most suitable for mass-rearing than S. littoralis. Conclusion: To increase the efficacy of M. gyrator as an endoparasitoid, its numbers in the field should be increased by releasing a considerable number of adults, to control lepidopterous larval pests.