Genetic diversity and host alternation of the egg parasitoid Ooencyrtus pityocampae between the pine processionary moth and the caper bug.

Shahar Samra,Alex Protasov,Manuela Branco,Murad Ghanim,Zvi Mendel,Youjun Zhang

doi:10.1371/journal.pone.0122788

Shahar Samra, Alex Protasov + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0122788

Copy DOI

Abstract

The increased use of molecular tools for species identification in recent decades revealed that each of many apparently generalist parasitoids are actually a complex of morphologically similar congeners, most of which have a rather narrow host range. Ooencyrtus pityocampae (OP), an important egg parasitoid of the pine processionary moth (PPM), is considered a generalist parasitoid. OP emerges from PPM eggs after winter hibernation, mainly in spring and early summer, long before the eggs of the next PPM generation occurs. The occurrence of OP in eggs of the variegated caper bug (CB) Stenozygum coloratum in spring and summer suggests that OP populations alternate seasonally between PPM and CB. However, the identity of OP population on CB eggs seemed uncertain; unlike OP-PPM populations, the former displayed apparently high male/female ratios and lack of attraction to the PPM sex pheromone. We studied the molecular identities of the two populations since the morphological identification of the genus Ooencyrtus, and OP in particular, is difficult. Sequencing of COI and ITS2 DNA fragments and AFLP analysis of individuals from both hosts revealed no apparent differences between the OP-PPM and the OP-CB populations for both the Israeli and the Turkish OPs, which therefore supported the possibility of host alternation. Sequencing data extended our knowledge of the genetic structure of OP populations in the Mediterranean area, and revealed clear separation between East and West Mediterranean populations. The overall level of genetic diversity was rather small, with the Israeli population much less diverse than all others; possible explanations for this finding are discussed. The findings support the possibility of utilizing the CB and other hosts for enhancing biological control of the PPM.

Highlights

The term "host alternation" is often used to describe situations in which species are required to change hosts constantly in order to survive, as in the case of true parasites that exhibit complex life cycles that require two different host species [1], or in the case of aphid species that alternate seasonally between two distinct host plant species [2]
The objectives of the present study were as follows: (1) to confirm the presence or absence of host alternation in Ooencyrtus pityocampae Mercet (OP), by determining the level of genetic similarity between OP populations from pine processionary moth (PPM) and caper bug (CB); and (2) to determine whether the apparently low genetic diversity in the Israeli OP population is unique to this area, or is a general phenomenon in this species
In every location where the CB egg masses were collected, other Ooencyrtus spp. were parasitizing the eggs, usually substantially outnumbering OP; in some locations no OP individuals were found in the CB eggs sampled, e.g., the Negev desert and Jordan Valley, these samples were not included in the present work

Summary

Introduction

The term "host alternation" is often used to describe situations in which species are required to change hosts constantly in order to survive, as in the case of true parasites that exhibit complex life cycles that require two different host species [1], or in the case of aphid species that alternate seasonally between two distinct host plant species [2]. Wide application of molecular techniques in recent decades revealed that many of those designated as "generalist parasitoids" are a complex of several closely related and morphologically similar species each [10,11], described as "cryptic" or "sibling species" [12,13]. These segregated species often utilize different hosts; many of them have rather narrow host ranges and can be considered specialists [10,11]. OP is common in Israeli pine forests, where it is the dominant egg parasitoid attacking the PPM eggs in this area, responsible for substantial egg mortality rates—up to 80% in a single egg mass [21]

Objectives

Methods

Conclusion