Biology of tachinid parasitoids (diptera) and their role in biological control of leafrollers (Lepidoptera: Tortricidae) in Washington tree fruit.

摘要

The tachinid flies Nemorilla pyste (Walker) and Nilea erecta (Coquillett) (Diptera) are important parasitoids of leafroller pests (Lepidoptera: Tortricidae) in central Washington tree fruits. Commercial orchard sites in central Washington were sampled from 2006-2010 for leafroller larvae, which were reared to collect parasitoids. The flies were widely distributed, and N. pyste was more frequently collected than N. erecta. The lifestage of host larvae and the time of collection determined that host size preferences and phenology were similar. The flies were reared in the laboratory and dissected in order to determine their reproductive biology. Nemorilla pyste was found to be a highly synovigenic oviparous species, while N. erecta was found to be moderately synovigenic and ovolarviparous. Longevity and fertility of the parasitoids and mortality of the leafroller Choristoneura rosaceana Harris were examined in a life table study with variable host density. Nemorilla pyste had higher fertility because females were able to adjust oviposition to the number of hosts available, while N. erecta lacked this ability, and had poor control over self-superparasitism. Despite lower reproductive rates, N. erecta may have greater effect on leafroller populations because superparasitism eliminated hosts. Egg allocation of N. pyste attacking C. rosaceana was also examined in a demographic context. While large clutches may at times be necessary to ensure production of offspring when hosts are rare, they were associated with higher fitness costs such as reduced offspring survival, increased developmental time, and decreased male body size. Life history of the immature stages of these endoparasitoids was studied to examine potential mechanisms for competitive interactions including development rates, respiration-mediated competition, selective starvation, tolerance, and physical interference. Intra- and interspecific competition in the host was also experimentally manipulated to examine outcomes. The two parasitoids had distinct respiration strategies but similar development rates. Strong evidence of intraguild predation by N. erecta was found and the species tended to dominate N. pyste in interspecific interactions. Finally, compatibility of adult flies with residues of the insecticides pyriproxyfen and methoxyfenozide was investigated. Pyriproxyfen had strong effects on survival of the flies that was shown to have detrimental effects on projected fertility rates.