The effect of temperature on host patch exploitation by an egg parasitoid

The effect of temperature during host patch exploitation by parasitoids remains poorly understood, despite its importance on female reproductive success. Under laboratory conditions, we explored the behaviour of Anaphes listronoti, an egg parasitoid of the carrot weevil, Listronotus oregonensis, when foraging on a host patch at five temperatures. Temperature had a strong effect on the female tendency to exploit the patch: A. listronoti females parasitized more eggs at intermediate temperature (20 to 30°C) compared to those foraging at the extreme of the range (15.9°C and 32.8°C). However, there was no difference in offspring sex-ratio and clutch size between temperature treatments. Mechanisms of host acceptance within a patch differed between temperatures, especially at 32.8°C where females used ovipositor insertion rather than antennal contact to assess whether a host was already parasitized or not, suggesting that host handling and chemical cues detection were probably constrained at high temperature. Females spent less time on the host patch with increasing temperatures, but temperature had no effect on patch-leaving rules. Our results show that foraging A. listronoti females behave better than expected at sub-optimal temperatures, but worse than expected at supra-optimal temperatures. This could impair parasitoid performance under ongoing climate change.

Host Patch Use and Potential Competitive Interactions Between Two Egg Parasitoids From the Family Scelionidae, Candidate Biological Control Agents of Bagrada hilaris (Hemiptera: Pentatomidae)

Two egg parasitoids from Pakistan, Gryon sp. nr. gonikopalense Sharma (Hymenoptera: Scelionidae) and Trissolcus hyalinipennis Rajmohana & Narendran (Hymenoptera: Scelionidae), are currently being investigated as potential classical biocontrol agents for Bagrada hilaris Burmeister. The former is the most promising because of its ability to attack B. hilaris eggs in soil, but the latter was recently discovered in California. This study detailed the patch use and oviposition behavior of both species and assessed their relative foraging efficiency. We also investigated possible competitive interactions by assessing 1) the occurrence of intra- and interspecific host discrimination, 2) mutual interference between females (extrinsic competition), 3) the outcome of multiparasitism (intrinsic competition), and 4) the effect of competition on host suppression. Our results showed that T. hyalinipennis females tended to probe repeatedly in the same hosts leading to longer host patch time and lower foraging efficiency. Both species avoided conspecific superparasitism, but not multiparasitism. When the two species foraged simultaneously, G. sp. nr. gonikopalense seemed to be slightly superior in extrinsic competition, while neither species seemed to have an advantage in intrinsic competition. Also, neither species could develop as a facultative hyperparasitoid, but they inflicted non-reproductive mortality on eggs containing 4-d-old larvae of their competitor. Lastly, host mortality inflicted by G. sp. nr. gonikopalense and T. hyalinipennis when acting together appeared to be additive. These results suggest that the presence of T. hyalinipennis in California is unlikely to reduce G. sp. nr. gonikopalense efficiency, but will instead improve the biological control of B. hilaris.

Patterns of Oviposition and Feeding in the Monophagous Fly Anastrepha spatulata (Diptera: Tephritidae) on its Larval Host Plant Schoepfia schreberi

Monophagous insects that use discrete resources for oviposition and feeding are especially sensitive to variations in host quality and availability because their opportunities to find these resources are scarce. The monophagous tephritid fly Anastrepha spatulata Stone is a tephritid fly that uses as hosts the fruits of the non-economically important Schoepfia schreberi J. F. Gmel. Scant information of host utilization behavior in the field is available for this species. Wild individually marked flies were observed during the fruiting season. Observations of oviposition, feeding and resting on three trees were taken hourly from 0900 to 1800 hours on days with benign weather. Our results suggest that females can use fruits for oviposition or for feeding according to a temporal scale. Females were significantly more likely to feed on smaller hosts and oviposit in larger ones. Additionally, individual variation in host patch exploitation was detected. However, females that fed on a natural food source such as host fruit juice oviposited fewer eggs than females provided an artificial diet of sucrose and hydrolyzed yeast. Results indicate that females use different foraging tactics during the fruiting season and confirm that, in this case, the host plant is not the center of activity.

Parasitism of Tuta absoluta in tomato plants by Trichogramma pretiosum Riley in response to host density and plant structures

One important factor determining the efficacy of parasitoids is the way they exploit different host patch. This study evaluated the response of females of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) to the oviposition sites of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) on processing tomato plants. In fully developed caged tomato plants T. absoluta moths were released, followed by the release of T. pretiosum females 12h later. After 24h of parasitoid release, the moth oviposition sites were mapped according to the plant canopy, and levels of parasitism assessed. The parasitism rate varied from 1.5 to 28%. There was not influence of plant structures on parasitism, except for the absence of parasitism on the plant apex. Levels of both T. absoluta oviposition and parasitism by T. pretiosum were higher on the upper third of the plant, decreasing downward along the plant canopy.