# Aboveground and Belowground Male Population of the Invasive Citrus Mealybug Delottococcus aberiae De Lotto (Hemiptera: Pseudococcidae)

## TL;DR

This study reveals that the invasive citrus mealybug has a hidden belowground population, which is crucial for effective pest control.

## Contribution

The discovery of a previously unknown belowground male population of D. aberiae and a new sampling method for monitoring it.

## Key findings

- The mealybug has a permanent belowground population near citrus tree trunks.
- A new sampling method using pheromone-baited traps detects winter and spring populations.
- Natural enemies like Bdellidae mites and Hymenoptera parasitoids are active belowground.

## Abstract

D. aberiae is a new invasive pest introduced into Spain in 2009. It causes severe damage by deforming fruits, and controlling it is challenging. Our study demonstrates that, in addition to living aboveground, this pest has a permanent belowground population, previously unknown. It is distributed throughout the surface area between the rows of trees and more abundant near the trunk, and consequently this belowground population must be considered when controlling this pest. Special attention should be paid to the first generation of this insect, which develops in the soil during winter and by early spring has moved to fruit. To help monitor these early populations, the authors propose a simple and practical belowground sampling method consisting of using trays with sticky traps baited with sexual pheromone. This allows for the detection of winter and early spring populations and analyzes potential ways to reduce this population.

The invasive Delottococcus aberiae is one of the most harmful mealybugs on citrus in Spain, since it causes deformations and the premature falling of fruits in citrus orchards. To improve control strategies, this study evaluates its population above- and belowground, their distribution in the soil in addition to identifying natural enemies. The distribution in the soil of emerged males varies significantly with the distance to the tree trunks with an annual average number of 0.95 males/trap/day at 0.5 m, and ranging between 0.25 and 0.32 at 1 m, 1.5 m and 2 m. There is a consistent emergence of males throughout the year, both above- and belowground, with four distinct peaks, the first two occurring in February and April. This observation is essential to manage fruit damages that follows between March and June. Among the natural enemies detected belowground the following are highlighted: Bdellidae mites (52%), Hymenoptera parasitoids (16%) and spiders (11%). When implementing IPM strategies, emphasis should be placed on adequate soil management (crops, mulching, or the release of natural enemies) and to the appearance of first generation. We propose a belowground population sampling method as a simple and practical tool to quantify this pest’s the winter and spring populations, which remain undetectable using current methodologies.