Selective Predation Of The Pulli-Carrying Pardosa Pseudoannulata

The pond wolf spider Pardosa pseudoannulata(Araneae,Lycosidae)is a wandering spider with wide distribution and a large population in the agricultural ecosystem in China.It has a wide spatial niche and impressive predation ability,and can prey on many kinds of rice pests such as planthopper and leafhopper,being the one of the dominant predators in paddy field.Cannibalism is common among spiders.Some field observations have shown that the predation of a female of Lycosidae changed before and after oviposition,and the predation behavior of female tarantulae in pulli-carrying females was restrained to avoid eating the young tarantulae by mistake.In previous laboratory studies,we found that pullicarrying females did not predate newborn juveniles(mainly pulli)they encountered.This is undoubtedly a strategy used by Pardosa pseudoannulata to keep the population stable.However,details of this peculiar behavior change remain to be investigated.Therefore,we asked:(1)how much food a female consumes at different stages?(2)does food consumption variation contribute to the elimination of cannibalism on pulli of pulli-carrying females?(3)What is the response of pulli-carrying females to juveniles rather than pulli?(4)Does olfactory communication contribute to the selective predation of pulli-carrying females? In the present study,the female P.pseudoannulata were fed consecutively with the brown planthopper(BPH)Nilaparvata lugens and examined for their average food consumption at different stages,and then the predation selectivity on and olfactory response to various preys were examined through double-choice experiment,and Y-maze assayand EAG assay,respectively.Lastly,the predation and olfactory selectivity of females at other stages than pulli-carrying were also determined.The results will expand people understanding on the population maintenance and predation regulation of P.pseudoannulata,and facilitate the large-scale rearing and application in pest management.1.Predation selectivity and olfactory function of pulli-carrying femalesWe firstly measured the food consumption of females at five different stages,namely virgin,pre-oviposition,eggsac-carrying,pulli-carrying,and ovipositon interval.The average daily food consumption of virgins was 18.97±0.70 mg,pre-ovipostion females consumed19.76±0.55 mg,eggsac-carrying females fed on 7.84±0.50 mg,pulli-carrying mothers took12.56±0.87 mg food,and females at oviposition interval predate 9.96±0.96 mg on average.The amount of preys decreased after egglaying,but the predation amount in the pulli-carrying was slightly higher than that in the eggsac-carrying,indicating that the female spiders in the negative juvenile stage had normal predation ability.The predatory selection experiment showed that the pulli-carrying females exhibited a significant preference for preying on BPH,do not prey on pullus and dispersing juvenile.The Y-maze experiment showed that the pullicarrying females were strongly attracted by BPH,DJ,and 35d-juveniles,but had a much lower tendency towards to pulli.We extracted the low volatile cuticular substances of pulli and DJ with n-hexane,and EAG assay showed that pulli-carrying females responded to the extracts from the young juveniles at both stages activly.2.Predation selectivity and olfactory function of females rather than pulli-carryingWe also observed and recorded the predation selectivity of non-pulli-carrying females that were females at other stages than pulli-carrying.Among the three food-choice combinations,the predation ratio of BPH vs pullus was 52.02 vs 47.98 in combination(1);BPH vs DJ was58.84 vs 41.16 in combination(2),and pullus vs DJ was 54.19 and 45.81 in combination(3).Therefore,non-pulli-carrying females had no preference over BPH,pullus and DJ with intensive cannibalistic behavior.The Y-maze experiment showed that non-pulli-carrying females were attracted equally by the three types of prey.In summary,the present study demonstrated that the cannibalistic behavior of pullicarrying female P.pseudoannulata altered to be selective without predating the young juveniles(pullus and dispersing juveniles)compared to females at other stages,and a possible olfactory regulation was likely to be involved through the cuticular substances from young juveniles.The study is helpful for us to study the cannibalism and predation behavior of P.pseudoannulata and Lycosidae,and is of great significance to further understand their living habits and to protect the natural enemy resources.