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.

The detection of Anaphes sp. nov. [Hymenoptera : Mymaridae], an egg parasitoid of the carrot weevil in Nova Scotia

The wasps Anaphes victus (Huber) and Anaphes listronoti (Huber) [Hymenoptera : Mymaridae] parasitize 50% of the eggs of carrot weevil, Listronotus oregonensis (Le Conte) [Coleoptera : Curculionidae] in Quebec and in Ontario. Attempts to detect either of these egg parasites from exposed carrot weevil eggs in Nova Scotia were unsuccessful. However, 48 individuals of a new species of parasitic wasp, Anaphes sp. nov. [Hymenoptera : Mymaridae], were detected in carrot (Daucus carota) fields in Nova Scotia, using carrots infested in growth chambers with carrot weevil eggs. Anaphes sp. nov. is distinguishable from the other parasites of the carrot weevil by characteristics of the forewing. Anaphes sp. nov. has a forewing length : width ratio greater than 7 :3 while A. victus and A. listronoti have a forewing length : width ratio of less than 6 : 7.

DESCRIPTION OF THREE NEWANAPHESSPECIES (HYMENOPTERA: MYMARIDAE), EGG PARASITOIDS OF THE CARROT WEEVIL,LISTRONOTUS OREGONENSIS(LECONTE) (COLEOPTERA: CURCULIONIDAE), AND REDESCRIPTION OFANAPHES SORDIDATUSGIRAULT

Three new mymarid egg parasitoids of the carrot weevil,Listronotus oregonensis(LeConte) (Coleoptera: Curculionidae), are described:Anaphes coteiHuber from Nova Scotia;Anaphes listronotiHuber from Quebec; andAnaphes victusHuber from Quebec, Michigan, and Texas. A key to the species is given.Anaphes sorditatus(Girault), with which at least one of the new species was previously confused, is redescribed. Althoughlistronotiandsorditatuscannot presently be distinguished morphologically, they are biologically distinct and have different hosts. Crosses between malesordidatusand femalevictusyielded female offspring in 27% of the tests but none in the reciprocal crosses. The corresponding control crosses resulted in 90 and 30% female offspring. Mating did not occur in attempts to crosssordidatuswithlistronoti. On three occasions an unidentified species ofAnagruswas reared from field-collected carrot weevil eggs. This represents the first report of anAnagrusspecies from Curculionidae.