Sexual maturation and aging of adult male mealybug (Hemiptera: Pseudococcidae)

The ultrastructure of nymphal dermal pores and the genitalia of adult male of Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

The cotton mealybug, Phenacoccus solenopsis, has established itself as an invasive insect pest worldwide. It causes structural and physiological damage to various crops and can cause substantial financial losses in their production. The successful reproduction of this pest under a wide range of conditions is a key to its success. Despite this, the morphology of its genitalia, genital sensilla, and wax-producing dermal pores has received little attention, with little descriptions of their ultrastructure. By investigating those features with SEM, the present study revealed considerable new insights into the identification of the nymphal and adult stages of P. solenopsis. In addition, the description of the ultrastructural genital morphology of the immature stages of P. solenopsis has revealed characteristics that facilitate their discrimination. Trilocular pores were observed on both sides of the body, while the quinquelocular pores were distributed only on the ventral surface in both the first and second nymphal instars. The adult male is characterized by two pairs of waxy caudal filaments surrounded by clusters of 55 to 60 stellate pores, and each pregenital segment bears a pair of stellate pores composed of 4 or 5 peripheral loculi. Sensilla trichodea and numerous microtrichia are present on the pregenital segments. The penile sheath bears three subtypes of sensilla basiconica and also campaniformia, whereas the style bears three subtypes of sensilla campaniformia. The findings of this study could assist in the identification of the adult and nymphal stages of P. solenopsis, and also provide insights into the structures found on the genitalia of the adult male that possibly have an important role in mating events and copulatory behavior. Furthermore, these findings were able to contribute to better understanding the functional morphology of P. solenopsis.

A Novel Insect Overwintering Strategy: The Case of Mealybugs

Insects have limited ability to regulate their body temperature and have thus required a range of strategies to withstand thermally stressful environments. Under unfavorable winter conditions, insects often take refuge under the soil surface to survive. Here, the mealybug insect family was selected for the study. Field experiments were performed in fruit orchards in eastern Spain. We used specifically designed floor sampling methods combined with fruit tree canopy pheromone traps. We found that in temperate climates, the large majority of the mealybugs move from the tree canopy to the roots during the winter, where they turn into belowground root-feeding herbivores to survive and continue underground the reproductive process. Within the rhizosphere, mealybugs complete at least one generation before emerging on the soil surface. The preferred area to overwinter is within 1 m in diameter around the fruit tree trunk, where more than 12,000 mealybug flying males per square meter can emerge every spring. This overwintering pattern has not previously been reported for any other group of insects showing cold avoidance behavior. These findings have implications at the winter ecology level but also at the agronomical level since treatments to control mealybug pests are, until now, only based on the fruit trees' canopy.

Genome and transcriptome analysis of the mealybug Maconellicoccus hirsutus: Correlation with its unique phenotypes

Mealybugs are aggressive pests with world-wide distribution and are suitable for the study of different phenomena like genomic imprinting and epigenetics. Genomic approaches facilitate these studies in absence of robust genetics in this system. We sequenced, de novo assembled, annotated Maconellicoccus hirsutus genome. We carried out comparative genomics it with four mealybug and eight other insect species, to identify expanded, specific and contracted gene classes that relate to pesticide and desiccation resistance. We identified horizontally transferred genes adding to the mutualism between the mealybug and its endosymbionts. Male and female transcriptome analysis indicates differential expression of metabolic pathway genes correlating with their physiology and the genes for sexual dimorphism. The significantly lower expression of endosymbiont genes in males relates to the depletion of endosymbionts in males during development.

Biparental mealybugs may be more promiscuous than we thought

Knowledge on the reproductive biology of target insect pest is essential for the effective implementation of pheromone-based pest management tactics. In mealybugs, the second largest family of scale insects, the existence of female multiple mating was recently suggested. In this study, we aimed at testing how general is this behavior in mealybugs, by investigating polygyny and polyandry in two cosmopolitan pest mealybugs, Planococcus citri and Pseudococcus calceolariae. Males of these species were able to mate an average of 11.9 and 13.3 females, respectively, during their lifespan. The number of fertilized females per male decreased with male age/mating history for both mealybugs. We found no differences in female fecundity and fertility, when fertilized by males with different mating history. When we used male age as a proxy of mating history, we observed a significant negative effect on female fecundity. The females of both species remained receptive after first copula and eventually mated multiple times. The percentage of remated females of P. citri decreased linearly with time since first copula, with some maintaining receptivity up to 24 h. Males showed no preference between virgin and mated females, in static-air olfactometer tests. We found no benefit of female multiple mating in relation to fecundity. In biparental mealybugs, the mating system of males is possibly scramble competition polygyny; and that of females is possibly polyandry, with female receptivity restricted to a relatively short period. We discuss the practical implications of the results for pest management.

Multiple Mating in the Citrophilous Mealybug Pseudococcus calceolariae: Implications for Mating Disruption

The citrophilous mealybug Pseudococcus calceolariae (Maskell) (Hemiptera, Pseudococcidae) is a primary pest of various crops, including grapevines. The use of insecticides against this species is difficult in most cases because its life cycle includes an extended duration of eggs, juveniles, and adults under the bark and on the roots. Pheromone-based control strategies can present new eco-friendly opportunities to manage this species, as in the case of Planococcus ficus (Signoret) and Planococcus citri (Risso). With this aim it is critical to understand behavioral aspects that may influence pheromone-based control strategies. Herein, the capability of males to fertilize multiple females was investigated, trying to understand whether this behavior could negatively impact the efficacy of mass trapping, mating disruption, or the lure and kill technique. Results showed that a P. calceolariae male can successfully mate and fertilize up to 13 females. The copulation time in subsequent mating events and the time between copulations did not change over time but the number of matings per day significantly decreased. In a further experiment, we investigated the mate location strategy of P. calceolariae males, testing the attractiveness of different loadings of sex pheromone on males in a flight tunnel. Males constantly exposed to 16 rubber septa loaded with the sex pheromone showed a significant decrease in female detection at 1 and 30 μg loadings (0.18 and 0.74 visits per female for each visit per septum, respectively), whereas in the control about 9.2-fold more of the released males successfully detected the female in the center of the array of 16 septa without pheromone. Male location of females in the control (45%) was significantly higher than in the arrays with surrounding pheromone (5% and 20% at 1 and 30 μg loadings, respectively). Mating only occurred in the control arrays (45%). This study represents a useful first step to developing pheromone-based strategies for the control of citrophilous mealybugs.

Sexual attractiveness and reproductive performance in ageing females of a coccoid insect

Female age strongly influences reproductive success in various animals. Males are, therefore, expected to show preferential responses to sexual signals released from females of ages suitable for reproduction. Here, however, we report an unexpected and contradictory effect of ageing on sexual attractiveness and reproductive performance in a coccoid insect: the pheromone-based attractiveness of females increased with ageing, though their reproductive performance was in rapid decline. Surprisingly, senescent females continued releasing relatively high amounts of pheromone and maintained their sexual attractiveness, even at ages when they had almost completely lost fertility, with reduced densities of endosymbionts to support their physiology. Our dataset suggests a potential sexual conflict within a pheromone communication system, where females benefit at males' expense through deceptive signals of fertility.

Influence of mating disruption on the reproductive biology of the vine mealybug, Planococcus ficus (Hemiptera: Pseudococcidae), under field conditions

BACKGROUND

Although mating disruption is increasingly being used to control the worldwide grapevine pest vine mealybug, Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), its mode of action remains unclear. A 3-year field experiment was carried out to investigate the effects of mating disruption on the development and reproduction of the vine mealybug. The influence of mating disruption applied over consecutive years on the pest population density was also evaluated.

RESULTS

The percentage of ovipositing females was significantly reduced in disrupted plots by 18.8-66.2%, depending on the year. The absence of ovipositing females in disrupted plots in the autumn of the second and third years indicates the effectiveness of mating disruption throughout the whole growing season. Mating disruption consistently prolonged the pre-oviposition period in all years by up to 12.5 days.

CONCLUSION

Our findings provide new insights into the mechanisms underlying the pheromone-based control of the vine mealybug and indicate that the reduction of the pest population density is attributable to both a decrease and a delay in female mating. In addition, the population density of vine mealybugs under mating disruption decreased over the years, indicating that consecutive applications of this control strategy would significantly increase the effectiveness of control of the vine mealybug by mating disruption. © 2018 Society of Chemical Industry.

Monitoring Pseudococcus calceolariae (Hemiptera: Pseudococcidae) in Fruit Crops Using Pheromone-Baited Traps

The citrophilus mealybug, Pseudococcus calceolariae (Maskell), is an important pest of fruit crops in many regions of the world. Recently, its sex pheromone has been identified and synthesized. We carried out field experiments with the goal of developing monitoring protocols for P. calceolariae using pheromone-baited traps. Traps checked hourly for 24 hours showed a distinct diel pattern of male flight, between 18:00 and 21:00 h. The presence of unnatural stereoisomers did not affect trap captures, with isomeric mixtures capturing similar amounts of males as the biological active isomer. Dose of isomeric mixture pheromone (0-100 µg) had a nonlinear effect on male captures, with 10, 30, and 50 µg capturing similar amounts. The effective range of pheromone traps was determined by placing traps at different distances (15, 40, and 80 m) from an infested blueberry field, loaded with 0, 1 and 25 µg of the pheromone. For all distances, 25 µg dose captured more males, and was highly attractive up to 40 m. There was a significant effect of lure age on male captures (0-150 d), with similar amount of males captured up to 90-day-old lure, and lower captures in the 150-day-old lure compared with fresh ones. We found significant positive correlations between P. calceolariae males caught in pheromone traps with female abundance and fruit infestation at harvest. Our results show the usefulness of P. calceolariae pheromones for monitoring at field level and provide information for the design of monitoring protocols.