The prey preference of Dicrodiplosis manihoti Harris (Dip.: Ceccidomyiidae) to different developmental stages of the cotton mealybug Phenococcus solenopsis Tinsely (Hem.: Pseudococcidae)

Document Type : Complete paper

Authors

• Tahere Poorzandian ¹
• Leila Ramezani ²
• Sara Zarghami ³

¹ Departmen of Plant Protection, Faculty of Agriculture, Agricultural Science and Natural Resources University of Khuzestan, Mollasani, Iran

² Department of Plant Protection, Faculty of Agriculture, Agricultural Science and Natural Resources University of Khuzestan, Mollasani, Iran

³ Date Palm and Tropical Fruits Research Center, Horticultural Science, Research Institute, Ahvaz, Iran.

Abstract

Keywords

• Cotton mealybug
• Gall midge
• Manly index
• Pray preference

Main Subjects

• Biocontrol of pests

Extended Abstract

Introduction

The cotton mealybug, Phenococcus solenopsis Tinsely, is one of the destructive plant pests that is native to America and has become an important and dangerous pest in Asia in the 21st century (Wang et al., 2012; Fand et al., 2010; Hodgson et al., 2008). This polyphagous pest has a wide host range and has been collected from 219 species belonging to 159 genera from 70 families of plants including trees, shrubs, agricultural and non-agricultural plants in Iran (Mossadegh et al., 2015). Studies carried out on the natural enemies of mealybugs in Iran led to the identification of a predatory species Dicrodiplosis manihoti Harris (Diptera: Cecidomyiidae) in the southwestern regions of Iran (Bushi, 2016; Mossadeqh et al., 2015; Gheibi et al., 2015). Preliminary field and laboratory observations have shown that D. manihoti can probably have a high efficiency in controlling the cotton mealybug (Zilaei et al., 2022). The present study investigated the preference of different larval instars of this important predator on different developmental stages of cotton mealybug P. solenopsis.

Material and Methods

Samples of the cotton mealybug P. solenopsis were collected as pray from the Chinese hibiscus located in the campus of the University of Agricultural Science and Natural Resources University of Khuzestan and transferred to the laboratory and after the emergence of first instar nymphs they were transferred to the young branches of Chinese hibiscus in rearing containers. In order to create the initial population of D. manihoti, the infected branches contained mosquito larvae were placed in ventilated containers and after the emergence of adults, they were placed in ventilated containers with dimensions of 4×7×9 cm. containing cotton mealybugs. The colony was kept in an incubator at the temperature of 27 ± 1°C, relative humidity of 65 ± 10% and a photoperiod of 10:14 hours (darkness: lightness). Since a cohort of individuals was needed to experiment, a number of adult male and female mosquitoes were released on the colony of cotton mealybugs (including all developmental stages of the mealybug) and kept in an incubator with the optimum temperature, 32°C (Zilaei et al., 2022), relative humidity of 65±10% and photoperiod of 10:14 hours (darkness: light) and after 12 hours the adults were separated, then the laid eggs were collected and stored in separate containers. At the same time with the emergence of first instar mosquito larva, an equal number (density 16, in order to bring the density to a density of prey in which at least 50% of the prey has been consumed, i.e. density 64) of the developmental stages of 1^th, 2^d, and 3^d instars nymphs and adult females of mealybug were provided to each predator. After 24 hours, the predator was removed and the number of eaten pray from each developmental stage was recorded. This process was repeated for second and third instar larvae and adult male and female of D. manihoti with 20 repetitions. The data obtained from pray preference were analyzed using Manly's beta index (Manly, 1972). In order to evaluate the normality of the data, the Shapiro-Wilk test was used at the level of P=0.05 using SigmaPlot 12.0 software. Data analysis and comparison between treatments were performed using Tukey's test at P=0.05 level.

Results

The results of the pray preference of first, second and third instar larvae of D. manihoti by feeding on the first, second and third instar nymphs and adult stages of cotton mealybug at 32℃, relative humidity of 65 ± 10% and photoperiod 10:14 hours (darkness: lightness) using Manley's beta index showed the predator consumed all the developmental stages of the prey, but the amount of consumption of the developmental stages of the predator from the different developmental stages of pray were different.

Comparison of the average beta index for the first instar larva of D. manihoti showed that this developmental stage significantly prefers adult female to other developmental stages (P<0.006, df=3,76 H=12.57). Also the second instar larvae of D. manihoti significantly prefers first-instar nymph to other developmental stages and the lowest consumption of this stage was from the adult female mealybug with a significant difference from the nymphs of second and third instars (P<0.001, df=3,76 H=55.65). Comparison of the beta index in the third instar larvae of D. manihoti feeding on mealybug showed that the first instar nymphs were the preferred pray and the lowest consumption was from the adult mealybug (P<0.001, df=3,76 H=35/82).

Discussion

According to the results of this research, the predator’s first instar larvae preferred cotton mealybug adults over other developmental stages. The reason for this preference seems to be related to the low mobility of the adult mealybug. Since the amount of energy obtained from prey and the rate of prey capture is a function of prey size, larger prey may be preferred due to their higher nutritional value (Charnoff, 1976). Also second and third instars larvae of D. manihoti preferred mealybug nymphs more than other stages. The reason for this preference is probably related to the more mobility of older larvae and adult predator, so they choose smaller prey because the time to reach the prey is reduced and the availability and feeding of the prey is increased (Tinbergen, 1981). The results of this research showed that eating the most important developmental stage of the host, which can be transferred to other plants, increases the importance of this natural enemy. However, obtaining other behavioral information such as functional response, numerical response and its host preference in nature can play a role in making decisions about this biological agent.