Influence of competition and intraguild predation between two candidate biocontrol parasitoids on their potential impact against Harrisia cactus mealybug, Hypogeococcus sp. (Hemiptera: Pseudococcidae)

Effect of egg production dynamics on the functional response of two parasitoids

Functional response describes the number of hosts attacked by a parasitoid in relation to host densities and plays an important role by connecting behavioral-level processes with community-level processes. Most functional response studies were carried out using simple experimental designs where the insects were confined to a plain and small arena with different host densities during a fixed period of time. With these designs, other factors that might affect the functional response of parasitoids were not analyzed, such as fecundity, age, and experience. We proposed a series of latent-variables Markovian models that comprised an integrated approach of functional response and egg production models to estimate the realized lifetime reproductive success of parasitoids. As a case study, we used the parasitoids Anagyrus cachamai and A. lapachosus (Hymenoptera: Encyrtidae), two candidate agents for neoclassical biocontrol of the Puerto Rican cactus pest mealybug, Hypogeococcus sp. (Hemiptera: Pseudococcidae). The tested species were assessed according to their physiology and prior experience. We estimated the number of mature eggs after emergence, egg production on the first day, egg production rate, the proportion of eggs resorbed, egg resorption threshold, and egg storage capacity. Anagyrus cachamai and A. lapachosus both presented a type III functional response. However, the two parasitoids behaved differently; for A. cachamai, the number of parasitized hosts decreased with female age and depended on the number of mature eggs that were available for oviposition, whereas A. lapachosus host parasitism increased with female age and was modulated by its daily egg load and previous experience. The methodology presented may have large applicability in pest control, invasive species management, and conservation biology, as it has the potential to increase our understanding of the reproductive biology of a wide variety of species, ultimately leading to improved management strategies.

Lethal effect of Goniozus legneri on Cactoblastis cactorum: A potential biocontrol agent for inundative releases

Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), the cactus moth, is native to South America with a widespread distribution in Argentina. The larvae consume the interior of Opuntia spp. (Cactaceae) plants. The moth was used as a biocontrol agent against invasive non-native Opuntia spp. in many countries around the world. The cactus moth arrived unintentionally in Florida, USA, expanded its range and threatened Opuntia-based agriculture and natural ecosystems in southern North America. The insect is also a pest of cultivated O. ficus-indica L. in Argentina. An endemic South American parasitoid, Goniozus legneri Gordth (Hymenoptera: Bethylidae), is used in inundative biological control programmes against lepidopteran pests. The goal of this work was to evaluate G. legneri as a biocontrol agent to be used in inundative releases against C. cactorum. Mortality of C. cactorum by G. legneri was assessed at different spatial scales, as well as the interactions with Apanteles opuntiarum Martínez & Berta (Hymenoptera: Braconidae), a common Argentine natural enemy of C. cactorum. The ability of G. legneri to paralyse, parasitise and kill C. cactorum was confirmed. The paralysis inflicted on C. cactorum larvae reduced larval damage to the plants by 85%. Using two parasitoid species increased the mortality of C. cactorum larvae, but it was highly dependent on the order of their arrival. The combined mortality caused by both parasitoids was higher than a single one, in particular when G. legneri arrived first (56 ± 1%), suggesting asymmetric competition due to the preference of G. legneri attacking previously parasitised larvae. Goniozus legneri has potential as an inundative biocontrol agent of C. cactorum, but its interaction with the classical biocontrol agent A. opuntiarum needs to be considered.

Herbivory in Myrtillocactus geometrizans (Cactaceae): Do Parasitoids Provide Indirect Defense or a Direct Advantage?

Plants respond to herbivory in diverse, complex ways, ranging from avoidance or tolerance to indirect defense mechanisms such as attracting natural enemies of herbivores, i.e., parasitoids or predators, to strengthen their defense. Defense provided by parasitoids to cultivated plants is well documented and is used in biological control programs. However, its effectiveness on wild plants under natural conditions has been little studied. Such is the case of the cactus Myrtilllocactus geometrizans (known in Mexico as garambullo), which is consumed by the soft-scale insect Toumeyella martinezae (herbivore) which, in turn, is host to the parasitoid wasp Mexidalgus toumeyellus, and mutualist with the ant Liometopum apiculatum, that tenders and protects it. This study explores the role of the parasitoid as an indirect defense, by examining its effect on both the herbivore and the plant, and how this interaction is affected by the presence of the mutualistic ant. We found that scales adversely affect the cactus' growth, flower, and fruit production, as well as its progeny's performance, as seedlings from scale-infested garambullo plants were shorter, and it also favors the presence of fungus (sooty mold). The parasitoid responded positively to herbivore abundance, but the presence of ants reduced the intensity of parasitism. Our results show that parasitoids can function as an indirect defense, but their effectiveness is reduced by the presence of the herbivore's mutualistic ant.

Genomic and ecological evidence shed light on the recent demographic history of two related invasive insects

Hypogeococcus pungens is a species complex native to southern South America that is composed of at least five putative species, each one specialized in the use of different host plants. Two of these undescribed species were registered as invasive in Central and North America: Hyp-C is a cactophagous mealybug that became an important pest that threatens endemic cactus species in Puerto Rico, and Hyp-AP feeds on Amaranthaceae and Portulacaceae hosts, but does not produce severe damage to the host plants. We quantified genomic variation and investigated the demographic history of both invasive species by means of coalescent-based simulations using high throughput sequencing data. We also evaluated the incidence of host plant infestation produced by both species and used an ecological niche modeling approach to assess potential distribution under current and future climatic scenarios. Our genetic survey evinced the footprints of strong effective population size reduction and signals of genetic differentiation among populations within each species. Incidence of plant attacks varied between species and among populations within species, with some host plant species preferred over others. Ecological niche modeling suggested that under future climatic scenarios both species would expand their distribution ranges in Puerto Rico. These results provide valuable information for the design of efficient management and control strategies of the Puerto Rican cactus pest and shed light on the evolutionary pathways of biological invasions.