Do releases of the mirid predator Macrolophus basicornis (Hemiptera: Miridae) together with the egg parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) improve biological control of Tuta absoluta (Lepidoptera: Gelechiidae) in tomato?

During the past decade, the use of predatory mirids alone or combined with releases of egg parasitoids of the genus Trichogramma have been tested in Europe for biological control of the worldwide invasive pest, Tuta absoluta (Meyrick). Here, we evaluated the control of this pest by the release of the Neotropical mirid Macrolophus basicornis (Stal), the Neotropic/Nearctic parasitoid Trichogramma pretiosum Riley, and by combined releases of the predator and the parasitoid. Tests were conducted in greenhouse compartments during the summer and fall season. Each compartment contained 10 tomato plants in which only the pest was released or the pest with 1 or 2 natural enemies. Plant damage, and pest and natural enemy densities were checked weekly on one apical, medium, and bottom leaf of 5 plants. Both M. basicornis and T. pretiosum significantly reduced T. absoluta density when released alone. Combined releases resulted in a 10% higher reduction during the summer season, but not during the fall season. The damage caused by T. absoluta was significantly higher in control treatments than in all natural enemy treatments: at the end of the summer trial leaves were completely damaged in the control treatment, whereas only up to 25% leaf damage occurred in the natural enemy treatments. Combined releases did not result in lower damage than with releases of either M. basicornis or T. pretiosum. Practical aspects of single and combined releases are discussed.

Biological Control with Trichogramma in China: History, Present Status, and Perspectives

Trichogramma species make up one of the most commonly used groups of natural enemies for biological control programs worldwide. Given the major successes in using Trichogramma to control economically important lepidopterous pests on agricultural crops in China, the biology and ecology of these wasps have been intensively studied to identify traits that contribute to successful biological control. Since the 1960s, improved mass production of Trichogramma and better augmentative release methods to suppress agricultural pests have been achieved. We review the history of research and development; current knowledge on biodiversity and bio-ecology of the species used; and achievements in mass-rearing methods, release strategies, and current large-scale applications in China. In addition, we discuss potential issues and challenges for Trichogramma research and applications in the future.

From laboratory to the field: consistent effects of experience on host location by the fruit fly parasitoid Diachasmimorpha kraussii (Hymenoptera: Braconidae)

Associative learning is well documented in Hymenopteran parasitoids, where it is thought to be an adaptive mechanism for increasing successful host location in complex environments. Based on this learning capacity, it has been suggested that providing prerelease training to parasitoids reared for inundative release may lead to a subsequent increase in their efficacy as biological control agents. Using the fruit fly parasitoid Diachasmimorpha krausii we tested this hypothesis in a series of associative learning experiments which involved the parasitoid, two host fruits (tomatoes and nectarine), and one host fly (Bactrocera tryoni). In sequential Y-tube olfactometer studies, large field-cage studies, and then open field studies, naïve wasps showed a consistent preference for nectarines over tomatoes. The preference for nectarines was retained, but not significantly increased, for wasps which had prior training exposure to nectarines. However, and again consistently at all three spatial scales, prior experience on tomatoes led to significantly increased attraction to this fruit by tomato-trained wasps, including those liberated freely in the environment. These results, showing consistency of learning at multiple spatial scales, gives confidence to the many laboratory-based learning studies which are extrapolated to the field without testing. The experiment also provides direct experimental support for the proposed practice of enhancing the quality of inundatively released parasitoids through associative learning.

Can Anastatus bifasciatus Be Used for Augmentative Biological Control of the Brown Marmorated Stink Bug in Fruit Orchards?

The generalist egg parasitoid Anastatus bifasciatus (Geoffroy) (Hymenoptera: Eupelmidae) is the most prevalent egg parasitoid of the invasive Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) in Europe. To assess its efficacy against the pest H. halys and to validate the potential risks for non-target species in a realistic field setting, inundative releases were conducted over three consecutive years in four fruit orchards in Switzerland and Italy. In total, more than 4300 A. bifasciatus females were released, which was equivalent to 11,000 to 26,000 females per hectare, depending on distances between trees in each orchard. Parasitism of freeze-killed sentinel H. halys eggs achieved with the current release strategy was on average 6% (range: 2%–16%) and considered not high enough to effectively suppress the pest. However, the overall impact of A. bifasciatus on the mortality of H. halys eggs was likely underestimated. If pre-imaginal parasitoid mortality (3.3%) and host feeding (6%) are added to the observed parasitism (6%), the actual induced mortality of H. halys eggs may reach more than 15%. Parasitism of lepidopteran non-target species reached an average of 8% and thus, some degree of non-target parasitism after mass releases may be expected. To quantify the impact of the parasitoids in the orchards more precisely, naturally laid egg masses should be used in future trials to include host-finding cues of the host and host plants, and larger scale releases with potentially higher densities of parasitoids should be considered.

Number of attacks by Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae) affects the successful parasitism of Ostrinia furnacalis (Lepidoptera: Crambidae) eggs

In laboratories, the parasitism rate of Ostrinia furnacalis (Güenée) (Lepidoptera: Crambidae) eggs by Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) is low; however, efforts to control O. furnacalis with T. dendrolimi in the field have been successful. In this study, the effects of the number of attacks by T. dendrolimi against O. furnacalis eggs and diet of O. furnacalis larva on wasp development were investigated. The results indicated that more attacks increased significantly not only the successful parasitism rate of O. furnacalis eggs by T. dendrolimi, but also the percentage of host eggs that failed to develop into either O. furnacalis larvae or T. dendrolimi. Both the size and female proportion of T. dendrolimi offspring decreased as the number of attacks increased. The number of T. dendrolimi eggs laid in per host egg increased significantly as the ratio of wasps to host eggs increased from 1:5 to 3:5. Host diet also significantly affected the developmental time of immaturity and the emergence rate of adults of T. dendrolimi. These results illustrate how inundative releases of T. dendrolimi can successfully control O. furnacalis despite the fact that pest parasitism by the subsequent wasp generation decreases sharply in the field. The suitability of O. furnacalis eggs to T. dendrolimi and the superparasitism effects on offspring of T. dendrolimi are discussed.

Assessing effects of the entomopathogenic fungus Metarhizium brunneum on soil microbial communities in Agriotes spp. biological pest control

The release of large quantities of microorganisms to soil for purposes such as pest control or plant growth promotion may affect the indigenous soil microbial communities. In our study, we investigated potential effects of Metarhizium brunneum ART2825 on soil fungi and prokaryota in bulk soil using high-throughput sequencing of ribosomal markers. Different formulations of this strain, and combinations of the fungus with garlic as efficacy-enhancing agent, were tested over 4 months in a pot and a field experiment carried out for biological control of Agriotes spp. in potatoes. A biocontrol effect was observed only in the pot experiment, i.e. the application of FCBK resulted in 77% efficacy. Colony counts combined with genotyping and marker sequence abundance confirmed the successful establishment of the applied strain. Only the formulated applied strain caused small shifts in fungal communities in the pot experiment. Treatment effects were in the same range as the effects caused by barley kernels, the carrier of the FCBK formulation and temporal effects. Garlic treatments and time affected prokaryotic communities. In the field experiment, only spatial differences affected fungal and prokaryotic communities. Our findings suggest that M. brunneum may not adversely affect soil microbial communities.

Allee effects in tritrophic food chains: some insights in pest biological control

Release of natural enemies to control pest populations is a common strategy in biological control. However, its effectiveness is supposed to be impaired, among other factors, by Allee effects in the biological control agent and by the fact that introduced pest natural enemies interact with some native species of the ecosystem. In this work, we devise a tritrophic food chain model where the assumptions previously raised are proved correct when a hyperpredator attacks the introduced pest natural enemy by a functional response type 2 or 3. Moreover, success of pest control is shown to be related to the release of large amounts (i.e., inundative releases) of natural enemies.