Interactions between the omnivorous bug Nesidiocoris tenuis (Heteroptera: Miridae) and the tomato pests Helicoverpa armigera (Lepidoptera: Noctuidae) and Phthorimaea absoluta (Lepidoptera: Gelechiidae): predation, phytophagy, and prey preference.

Nesidiocoris tenuis (Reuter) (Heteroptera: Miridae) is a zoophytophagous bug that can derive nutrients from 3 trophic levels: plants, herbivorous arthropods, and other predators. On tomato, besides damaging the plants as they feed, might the mirid also forage on pest species and repel pests. In greenhouse and laboratory experiments, we investigated the functional response of the bug, its prey preference, and its influence on the oviposition potentials of 2 major pest species Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) and Phthorimaea absoluta Meyrick (Lepidoptera: Gelechiidae) on tomato Solanum lycopersicum L. (Solanaceae). Nesidiocoris tenuis showed a Type II functional response to both prey species. The estimated handling time was higher for H. armigera eggs than for P. absoluta yet N. tenuis attack rates did not differ between the 2 prey species. Nesidiocoris tenuis did not show a preference for 1 species when prey eggs were provided in equal proportions. The feeding on tomato plants by N. tenuis did not affect oviposition by the 2 moth species, as neither species showed a preference for clean or N. tenuis-adult-damaged plants and clean or N. tenuis-nymph-damaged plants. This study shows that N. tenuis can prey upon eggs of both moth species as the 3 species co-occur in tomato fields. However, because of the shorter handling time of P. absoluta eggs by the predator and the higher number of eggs laid by H. armigera, the co-occurrence might be less detrimental to the H. armigera populations compared to P. absoluta.

Efficacy of a postharvest treatment aiming at eradication of all developmental stages of Tecia solanivora in ware potatoes.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver a scientific opinion on the efficacy of a postharvest treatment aiming to eradicate all developmental stages of Guatemalan potato tuber moth Tecia solanivora (Lepidoptera: Gelechiidae) in ware potatoes. The Panel evaluated the scientific publication describing the elevated CO2 treatment, which was defined as: 10-day exposure to 30% CO2, 20% O2 and 50% N2 in controlled atmosphere at 17°C on the variety Negra Yema de Huevo (Papas Antiguas de Canarias, PDO potatoes, Solanum chaucha). In the scientific publication, the treatment was applied under semi-commercial and commercial conditions on artificially and field-infested tubers. The effect of the pest developmental stage on the treatment efficacy was investigated with artificial infestation of potato tubers with eggs, neonate and second instar larvae. Pupae and adults were placed in separate containers during the treatment. However, the third and fourth larval instars were not investigated. Further limitations were the sample size in the experiments, the mortality rate in the control group and the unknown level of infestation of the naturally infested potato tubers. It was not possible to evaluate the degree of pest freedom due to incomplete data on the conditions of production, i.e. the infestation level in the field. The Panel was able to conclude that although no surviving insects were observed in the performed experiments, the statistical evaluation of the presented results from the commercial trial indicate that it cannot be excluded that insects would survive the treatment. For example, based on the data provided the 95% confidence interval of the survival rate for eggs was: 0%-0.453%.

Detection of Volatile Constituents from Food Lures by Tephritid Fruit Flies.

Tephritid fruit flies require protein for sexual and gonotrophic development. Food-based lures are therefore widely used in strategies to detect and control fruit flies in the Tephritidae family. However, these baits are attractive to a broad range of insect species. We therefore sought to identify volatiles detected by the fly antennae, with the goal to compose lures that more specifically target tephritids. Using gas chromatography-coupled electroantennographic detection (GC-EAD) we screened for antennal responses of four important tephritid species to volatile compounds from five commercially available protein-based baits. Antennal active compounds were reconstituted in synthetic blends for each species and used in behavioral assays. These species-based blends were attractive in olfactometer experiments, as was a blend composed of all antennally active compounds from all the four species we observed (tested only in Bactrocera dorsalis, Hendel). Pilot field tests indicate that the blends need to be further evaluated and optimized under field conditions.

Host-plant location by the Guatemalan potato moth Tecia solanivora is assisted by floral volatiles.

Insects locate their host plants using mainly visual and olfactory cues, generally of the exploited plant structure. However, when the resource is difficult to access, it could be beneficial to utilise indirect cues, which indicates the presence of reward (e.g., oviposition site or mate). In the present study, we investigated the host-plant location strategy of the monophagous Guatemalan potato moth Tecia solanivora (Lepidoptera: Gelechiidae). The larva of the moth feed exclusively on potato Solanum spp. (Solanaceae) tubers usually hidden below ground. Using electrophysiological and behavioural tests, we characterised the olfactory cues mediating the attraction of the moth towards their host plant. Odour blends were made to represent different potato structures: tubers, foliage, and flowers. Synthetic blends were created by combining potato-emitted compounds that were antennal active which showed positive dose-response. Attraction to these blends of compounds in relation to the mating status of males and females was tested in dual-choice Y-tube assays. Both males and females, virgin and mated, were attracted to a three-compound blend representing flower odour, while foliage and tuber blends attracted neither sexes. Oviposition bioassays indicated additionally that the floral blend enhances oviposition. We show that potato flower odour might indicate the presence of an oviposition site for the female and possibly an increased mating opportunity for both sexes. Our results provide one of the few examples of the use of floral odour as a reliable indicator of host and probably mating possibility for phytophagous insects exploiting a site spatially separated from the flower.

Identification of host blends that attract the African invasive fruit fly, Bactrocera invadens.

Bactrocera invadens, an invasive fruit fly species in the Afro-tropical region belonging to the Bactrocera dorsalis complex, causes considerable damage to fruit production and productivity. We sought to find attractants from hosts of B. invadens that could serve as baits in traps for monitoring and management of this pest. The attractiveness of volatiles from four different fruit species (mango, guava, banana and orange) at two stages of ripeness (ripe or unripe) was tested in an olfactometer assay. All fruits were attractive against a clean air control. Using hexane extracts of volatile collections of fruits, we demonstrated that male flies preferred the volatiles of ripe guava and orange over unripe fruit extracts. There was a slight difference in preference between females and males; females preferred orange to guava and mango, whereas males preferred mango and guava to orange. Gas chromatography/electroantennographic detection (GC/EAD) and GC/mass spectrometry (GC/MS) were used to identify compounds to which B. invadens antennae were sensitive. GC/EAD recordings from distal and medio-central parts of the fly antenna showed responses to a number of compounds from each fruit species, with esters dominating the responses. Synthetic blends were made for each fruit species using the shared antennally active compounds in ratios found in the extracts. In the olfactometer, B. invadens was most attracted to the banana and orange blends, followed by the mango and guava blends. The synthetic banana blend was as attractive as the volatile collection of banana, although both were less attractive than the fruit. The results demonstrate that composing attractive blends from GC/EAD-active constituents shared by host fruits can be effective for formulating attractive synthetic host mimics for generalist fruit fly species, such as B. invadens.

Guatemalan potato moth Tecia solanivora distinguish odour profiles from qualitatively different potatoes Solanum tuberosum L.

Guatemalan potato moth, Tecia solanivora, lay eggs in the soil nearby potato Solanum spp. and larvae feed on the tubers. We investigated the oviposition behaviour of T. solanivora females and the survival of larval offspring on healthy vs. stressed, i.e. light exposed and/or damaged potato tubers. In choice tests, females laid significantly more eggs in response to potato odour of healthy tubers and female oviposition preference correlated with higher larval survival. Survival of larvae was negatively correlated with the tuber content of the steroid glycoalkaloids α-solanine and α-chaconine: healthy potatoes contained lower amounts than stressed tubers, ranging from 25 to 500 µg g⁻¹ and from 30 to 600 µg g⁻¹, respectively. Analysis of volatile compounds emitted by potato tubers revealed that stressed tubers could clearly be distinguished from healthy tubers by the composition of their volatile profiles. Compounds that contributed to this difference were e.g. decanal, nonanal, isopropyl myristate, phenylacetaldehyde, benzothiazole, heptadecane, octadecane, myristicin, E,E-α-farnesene and verbenone. Oviposition assays, when female moths were not in contact with the tubers, clearly demonstrated that volatiles guide the females to lay fewer eggs on stressed tubers that are of inferior quality for the larvae. We propose that volatiles, such as sesquiterpenes and aldehydes, mediate oviposition behaviour and are correlated with biosynthetically related, non-volatile compounds, such as steroidal glycoalkaloids, which influence larval survival. We conclude that the oviposition response and larval survival of T. solanivora on healthy vs. stressed tubers supports the preference performance hypothesis for insect herbivores.

Plant odor analysis of potato: response of guatemalan moth to above- and belowground potato volatiles.

The Guatemalan moth Tecia solanivora is an invasive pest of potato in Central and South America. The larvae infest potato tubers in the field as well as in storage facilities. The headspace of potato foliage and potato tubers was studied with regard to volatiles that mediate host-finding and oviposition in the Guatemalan moth. Foliage of three phenological stages, from sprouting to tuberization and flowering, released more than 30 sesquiterpenes. The main compounds were beta-caryophyllene, germacrene-D-4-ol, germacrene-D, kunzeaol, and (E,E)-alpha-farnesene. Sesquiterpenes accounted for >90% of the headspace of green plants, whereas fresh potato tubers emitted only trace amounts of a few sesquiterpenes. Screening of headspace collections with antennae of Guatemalan moth females showed a strong response to several sesquiterpenes and monoterpenes that were emitted from foliage only. In addition, antennae responded to methyl phenylacetate, a floral fragrance that was released in large amounts from flowering plants and that was also present in tuber headspace. Female and male moths were attracted to methyl phenylacetate; this compound may accordingly contribute to female attraction to tuber-bearing potato plants in the field as well as to potato tubers in storage. Oviposition tests showed that females lay eggs near mature flowering plants. Eggs were laid in soil close to the plant and not on potato stems and foliage, which may be due to avoidance of terpenoid compounds released from green plant parts at close range. The results support the concept that potato volatiles mediate host-finding and oviposition behavior and that these compounds may become useful tools for management of the Guatemalan moth.