Weather Factors Affecting The Seasonal Population Dynamics of Black Melon Bug Coridius viduatus F. in New Valley, Egypt

The insect pest, known as Coridius (Aspongopus) viduatus F., is consistently found on plants belonging to the cucurbitaceous family (Shalaby, 1961). The C. viduatus is considered a significant pest on cucurbit plants, including melon, squash, marrow, and cucumber (Bohlen and Freidel, 1979). Walker and Pittaway's 1987 study revealed that C. viduatus significantly damages melon harvests. The black melon bug Coridius (Aspongopus) viduatus F. was recorded as a dangerous insect attacking cucurbit plants in Egypt, especially in New Valley Governorate, causing an economic reduction recording 50% in total cucurbit yield if an integrated pest management program is not implemented against it (Gameel, 2004). Also, it has been recorded as a dangerous pest on cucurbit crops in many countries, such as Turkey (Mariod, 2013), Saudi Arabia (Aljedani, 2018), and Sudan (Abdalla, 2010; Alla et al., 2015). Both adults and nymphs of the pest cause its damage by sucking the sap of the leaves, petioles, and stems, which wither and die (Mariod et al., 2007; Gameel and Sayed, 2008; Gameel, 2013).

The Coridius spp. was abundant on Cucurbitaceae in summer (March-September) and occasionally in winter (Sharma, 1990). The adults of the black melon bug, Coridius (Aspongopus) viduatus, were seen in the New Valley to be lethargic throughout the winter season. They were located in significant quantities beneath plant waste near the fields, particularly at the base of trees and shrubs (Bohlen and Freidel, 1979). The black melon bug has a consistent migration pattern from plant shelters, mountain crevices, and soil fissures to the field crop, followed by a return to aestivation locations (Gubartalla et al., 2018).

The black melon bug (BMB) is capable of completing its whole life cycle on watermelon in a laboratory setting. The duration from egg to adult stage of the squirting cucumber, when served as food at a temperature of 24 ± 2°C, was recorded as 5-6 weeks (Tarla et al., 2013). The average number of eggs laid by a single female was 448 ± 0.90 eggs. The insect has five instar nymphal stages over a period of around 40 days. Following the completion of the 5^th nymphal stage, the adult bug developed (Alla et al., 2015).

Temperature significantly influenced the duration of the black melon bug (BMB) life cycle. The insect took the longest time to complete its life cycle at 24°C, while the shortest duration was at 30°C. The mortality rate in immature stages increased as temperature rose from 24°C to 32°C. The lowest egg incubation time and nymphal duration were at 32°C, while the maximum duration was at 24°C (Gameel, 2004).

Limited research studies have been conducted on the impact of temperature, relative humidity, and wind speed on the biology and dynamics of C. viduatus in Egypt. This study investigates the influence of temperature, relative humidity, and wind speed on the seasonal abundance and population density of BMB infesting three cucurbit crops during the early summer and the Nili plantations throughout two consecutive seasons, from 2020 to 2021, in the New Valley Governorate.

MATERIALS AND METHODS

The average number of the black melon bug (nymphs and adults) seen each week on three cucurbit crops (cucumber, cantaloupe, and watermelon) was used to look at how four weather factors affect the bug numbers that appear at different times of the year. The daily records of the day’s maximum and minimum temperatures, relative humidity, and wind speed, as weather factors, were obtained from the Meteorological Station of El-Kharga City (which is about 1 km from the experimental site).

For insect-pest counting, individual nymphs and adults of the black melon bug, a simple square wooden wire of 0.25 m² (50x50 cm) was used as the standard sample size. Both stages of the pest (nymphs, and adults), were counted directly on the plants in a set of four-square wires (one sample =1m²).

The numbers of nymphs and adults of the black melon insect have been estimated using the direct counting method. The visual counts commenced following the third week of plant emergence and continued through the blooming and fruiting phases until harvest. Bug counts were conducted in both early summer and Nili plantations throughout two consecutive seasons, 2020 and 2021. The inspection period for the summer planting began on March 8 and ended on June 21 in 2020, while in 2021, it began on March 7 and continued on June 20. The inspection period for the Nili plantation began on September 6, 2020, and terminated on December 20, 2020, while for 2021, it spanned from September 5 to December 19. The plants underwent random inspections weekly throughout the inspection period, utilising four replicates of each cucurbit crop.

The seven-day count's data were considered the dependent variable (y), while the reading of corresponding weather factors represented the independent variables (x). The simple correlation values detect any possible relationship between the (y) and (x). Simple correlation (r) was estimated as well as the coefficient of determination (R²) (Stell and Torrie, 1960).

RESULTS AND DISCUSSION:

A)   The seasonal abundance and dynamics of the black melon bug in the early summer and Nili plantations during two successive seasons of 2020 and 2021:

The seasonal abundance of the black melon bug, C. viduatus (including both nymphs and adults), was investigated among three cucurbit crops (cucumber, cantaloupe, and watermelon) on two planting dates (early summer and Nili) during the 2020 and 2021 growing seasons. Table 1 and Figures 1 and 2 illustrate the population of black melon bug (BMB) on three different cucurbit crops during early summer and on Nili plantations in 2020.

Season 2020:

Early summer and Nili plantations 2020:

In the Early summer plantation 2020, recorded data in Table 1 and illustrated in Figure 1 revealed that the black melon bug, nymphs and adults, began to appear in the field on the three cucurbit crops in the third week of March, on March 22^nd (2.00, 5.50, and 1.00 individuals/m²) on cucumber, cantaloupe, and watermelon, respectively. This date coincided with max. & min. temp. 25.50°C & 10.40°C, RH = 37.50%, and wind speed = 8.48 km/h.

However, the population density of the BMB fluctuated in scarce numbers, attaining the first peak at the end of May on cantaloupe and watermelon (152.00 and 137.00 individuals/m²) and at the first week of April on cucumber (32.00 individuals/m²). The weather factors of this period were 31.33°C and 17.65 for max. and min. temp., RH = 28.25%, and wind speed = 6.35 km/h. Then numbers of the pest decreased in the next week and increased gradually in the third week of May (111.25, 428.75, and 239.00 individuals/m²), respectively, on the three cucurbit crops to build a big peak. The recorded weather factors were max. temp. = 44.40°C, min. temp. = 25.13°C, RH = 22.00%, and wind speed = 6.07 km/h when the plants were in the ripening stage. After that, the population density decreased at the end of May and the beginning of June.

In the Nili plantation 2020, as recorded in Table 1 and shown in Figure 2, the nymphs and adults of BMB began to appear in the second half of September, recording (0.25 and 0.25 individuals/m²) on cucumber and/or watermelon. On cucumber and cantaloupe, the number of individuals increased gradually to build up three peaks at the beginning and half of November and at the first week of December (81.00, 100.00, and 67.00 individuals/m²), respectively. During this time, the highest temperature, lowest temperature, relative humidity, and wind speed were recorded to be 38.7°C, 21.27°C, 27.35%, and 8.23 km/h at the first peak; 30.33°C, 16.95°C, 44.75%, and 8.53 km/h at the second peak; and 23.73°C, 9.27°C, 55.00%, and 3.83 km/h at the third peak. Two peaks of black melo bug showed on watermelon at the beginning and half of November (107.00 and 253.50 individuals/m²). The recorded weather conditions for the first and second peaks were 38.7°C, 21.27°C, 27.35%, and 8.23 km/h, and 30.33°C, 16.95°C, 44.75%, and 8.53 km/h, respectively. After that, the population density of the BMB declined during the growth stage of tested cucurbit crops.

Table 1: Mean of population density of C. viduatus (adults and nymphs) on three cucurbit crops during early summer and Nili plantations in 2020.

It is obvious that the population densities of the black melon bug among the cultivated cucurbit crops had two peaks represented in the last weeks of April and May in the summer plantation, and one peak on the second week of November in Nili plantation.

Fig. (1): Seasonal abundance of C. viduatus (nymphs and adults) on three cucubit crops during early summer palantation, 2020.

Fig. (2): Seasonal abundance of C. viduatus (nymphs and adults) on three cucubit crops during Nili palantation in 2020.