Academic literature on the topic 'Insect species'

It is generally believed that tree species growing in mixed forest stands are less susceptible to insect herbivore damage than if grown in monocultures, but previous studies have been largely observational and focussed mainly on tree species richness effects. In this thesis, I examined effects of three components of forest diversity (tree species richness, intraspecific genotypic diversity and functional diversity) on insect herbivores using three long-term forest diversity experiments in Finland and Germany. I have also explored the sources of variation in and the mechanisms behind the effects of tree diversity on insect herbivores. I found that all three components of forest diversity significantly influenced insect herbivore abundance and damage. Tree species richness effects depended on the insect herbivore feeding guild, but also changed within season and between years. As a result, silver birch (Betula pendula) experienced both associational resistance (reduced damage in mixed stands) and associational susceptibility (higher damage in mixed stands) to different insect herbivores and in some instances this altered temporally. In contrast, tree species richness effects on insect herbivory were spatially consistent and not mediated by tree size (physical apparency), physical properties of leaves or natural enemies. Interestingly, tree species richness and genotypic diversity had opposite effects on leaf miners; leaf miner abundance and species richness were lower in species-rich stands, but higher in mixtures containing several genotypes of silver birch. To test the effects of tree functional diversity, I created a functional diversity index based on constitutive emissions of monoterpenes and isoprene by different tree species and showed that tree species which emitted low levels of volatiles experienced associational resistance in stands with high diversity of volatile emissions. This suggests that increasing chemical complexity in mixed stands may interfere with host finding ability of herbivores.

Changes in the regulatory sequences of the genes involved in development are thought to be important in the evolution of morphology. However, molecular coevolution between functionally interacting genetic elements allows sequence divergence to be tolerated whilst the functional interaction is maintained. Molecular coevolution can lead to species-specificity in the sequence basis underlying molecular interactions. The concentration-dependent activation of hunchback (hb) expression in the anterior half of the Drosophila melanogaster embryo by the gradient of bicoid (bcd) protein represents a primary step in the elaboration of pattern along the anterior- posterior axis, and this interaction is conserved in the housefly, Musca domestica. In order to investigate the possibility that the molecular basis of this interaction may have coevolved, the bed and hb genes have been partially sequenced from M. domestica and compared to those of D. melanogaster. Analysis of the putative M. domestica hb regulatory region identified three candidate bed binding sites, with a consensus sequence of TTTAATCC, rather than the TCTAATCC of D. melanogaster. Comparison of the bed sequences revealed 5 changes within the 60 amino acids of the homedomain. Hence, it is possible that M. domestica bcd may have a subtly altered binding specificity, pointing towards the possibility that the coordinated changes in the binding site sequences have elicited compensatory changes in the M. domestica bed homeodomain. Preliminary analyses have been made of the functional significances of the observed differences. Although the functional significance of the observed differences in the bed and hb genes is not fully understood, the possibility remains that the molecular nature of the interaction between bed and hb has diverged between M. domestica and D. melanogaster.

Master of Science<br>Department of Grain Science and Industry<br>Bhadriraju Subramanyam<br>Hulya Dogan<br>Stored-product insects and stored products from feed mills and swine farms contain antibiotic and potentially virulent Enterococcus faecalis, Enterococcus faecium, Enterococcus casseliflavus, Enterococcus gallinarum, and Enterococcus hirae. Stored-product insects can serve as potential vectors of these enterococci which possess antibiotic resistance genes that can be spread by horizontal transfer to more serious human pathogens. In the present study, the species and concentration of enterococci from adults and larvae of key stored-product insects and insect diets and their antibiotic resistance profile were characterized. Adults of five species out of the 15 stored-product insects were tested positive for enterococci, and these included Callosobruchus maculatus (F.), Sitophilus granarius (L.), Stegobium paniceum (L.), Lasioderma serricorne (F.), and Sitophilus zeamais Motschulsky. Three enterococcal species (E. casseliflavus, E. faecalis, and E. faecium) were found in 53 to 97% of the 30 adults screened for each insect species, and the enterococcal concentrations ranged from 1.4 x 10³ to 3.1 x 10⁶ CFU/adult. About 10 to 100% of the mature larvae of the respective five insect species had these three enterococcal species with concentrations ranging from 0.3 x 10¹ to 1.4 x 10⁵ CFU/larvae. Only three of the eight insect diets screened had the same three enterococci species in addition to E. gallinarum and E. hirae at concentrations of 0.2 x 10¹ to 5.9 x 10³ CFU/g. The greatest enterococcal concentration was found in C. maculatus adults but not in their larvae or diet (cowpeas). In C. maculatus during a nine-day period after adult eclosion, the enterococcal concentrations increased exponentially from 0.6 x 10¹ to a maximum of 4.1 x 10⁷ CFU/adult. Enterococci were detected in the fecal material of C. maculatus during a four-day period with a maximum concentration of 3.3 x 10³ CFU/adult on the fourth day. A total of 298 enterococcal isolates from adults, larvae, and diets were represented by E. faecalis (51.7% of the total), E. faecium (19.1%), E. casseliflavus (18.8%), E. gallinarum (5.7%), and E. hirae (4.7%). Enterococci were phenotypically resistant to quinupristin (51.3% of the total), erythromycin (38.9%), tetracycline (30.1%), enrofloxacin (29.2%), doxycycline (11.5%), and tigecycline (2.7%). All isolates were susceptible to ampicillin and vancomycin.

Invasive species are alien to the ecosystem under consideration and cause economic or environmental damage or harm to human health. Two alien insects that fit this description are the brown marmorated stink bug, Halyomorpha halys and the spotted lanternfly, Lycorma delicatula. Both invaders are polyphagous pests that feed on a myriad of plant species and inflict severe crop losses. As sustainable control methods depend on the accurate monitoring of species’ invasion and involve the use of natural enemies, we addressed these two facets by exploring novel monitoring techniques and deciphering host-parasitoid interactions for improved integrated pest management. Thus, we adopted ‘BugMap’, a citizen science initiative that enables students, farmers and everyday citizens to report sightings of H. halys from Italy, with emphasis on Trentino-Alto Adige. Aside from fostering citizen participation in scientific endeavors and the enhanced literacy that ensues, BugMap helped uncover the invasion dynamics of H. halys and forecast its potential distribution in Trentino, all while coordinating technical monitoring and informing management strategies. The most promising agent currently under study for the classical biological control of H. halys is the Asian egg parasitoid Trissolcus japonicus. To assess the wasp’s potential non-target impacts, we investigated its foraging behavior in response to chemical traces ‘footprints’ deposited by its main host H. halys and by a suboptimal predatory species, the spined soldier bug, Podisus maculiventris. Wasps exhibited a ‘motivated searching’ when in contact with footprints originating from both species. However, T. japonicus arrestment was significantly stronger in response to H. halys footprints, compared with P. maculiventris, implying the presence of underlying chemical cues that shape its natural preferences. A series of GC-MS chemical analyses revealed that n-tridecane and (E)-2-decenal were more abundant in H. halys footprints and are probably the key components utilized by the wasp for short range host location. The function of the aforementioned compounds was studied, n-tridecane acted as an arrestant, prolonging T. japonicus residence time, whereas (E)-2-decenal fulfilled its presumed defensive role and repelled the wasp. These results shed new light on the chemical ecology of T. japonicus and help expand the understanding of parasitoid foraging and its implications for classical biological control. Moving to the other invader L. delicatula, an egg parasitoid Anastatus orientalis was reported attacking it at high rates in its native range in Eastern Asia and may play a key role in reducing its populations there. A series of bioassays revealed that wasps responded to footprints deposited by L. delicatula gravid females by initiating a strong searching behavior. Moreover, A. orientalis preferred to oviposit in egg masses with intact oothecae, suggesting that the host’s egg covering functions as a trigger for A. orientalis probing and oviposition. Thus, A. orientalis not only overcomes, but also reverses an important line of host structural defense for its own fitness gains. This dissertation discusses the benefits of combining citizen science with traditional monitoring, and the usefulness of decoding host-parasitoid interactions to design more efficacious management strategies of invasive insect pests.

Although it is well documented how introduced species can negatively affect native species, we only poorly understand how they may alter ecosystem functions. We investigated how an invasive fish affected the flux of aquatic insects to terrestrial food webs using mesocosms in a desert spring ecosystem. We compared aquatic insect emergence between alternative community states with monocultures and polycultures of two native species of fish, least chub (Iotichthys phlegethontis) and Utah chub (Gila atraria) plus, introduced western mosquitofish (Gambusia affinis). We tested three hypotheses: (1) aquatic insect biomass will be greater than terrestrial insect biomass and thus, constitute a vital source of energy for terrestrial consumers (2) invasive mosquitofish will negatively impact the biomass of emerging aquatic insects, and (3) terrestrial consumers will negatively respond to decreased emerging aquatic insect biomass. Aquatic insects represented 79% of the flying insect community, and treatments with mosquitofish significantly reduced emergent aquatic insect biomass by 60% relative to the control without mosquitofish. Behavioral traits of invasive species are important, because mosquitofish most heavily affected insects that emerged during the day. Also, spiders that build horizontal webs were negatively correlated with decreasing aquatic insect biomass. Invasive mosquitofish can achieve very dense populations because of their high intrinsic rate of population increase, which can significantly disrupt the flow of energy between aquatic and terrestrial ecosystems, thereby reducing the energy available for terrestrial consumers.