Intraguild Predation by Anthocoris nemorum (Heteroptera: Anthocoridae) on the Aphid Parasitoid Aphidius colemani (Hymenoptera: Braconidae)

The magnitude of intraguild predation by adult females of the predator Anthocoris nemorum on immature larvae of the aphid parasitoid Aphidius colemani inside mummies of peach-potato aphids Myzus persicae was investigated under laboratory conditions in a preference experiment. Each predator consumed a mean (95% confidence limits) of 2.8 (2.1; 3.8) immature parasitoids within mummies and 3.6 (2.7; 4.6) unparasitised aphid nymphs. Thereby A. nemorum engaged in intraguild predation with A. colemani and did not exhibit prey preference between mummies and unparasitised aphids.     

High oviposition rate ofDasineura marginemtorquens onSalix viminalis genotypes unsuitable for offspring survival

A short history of contact betweenDasineura marginemtorquens and resistant genotypes ofSalix viminalis has previously been suggested as an explanation for a poor correspondence between female oviposition preference and larval performance on certain host types. The discovery of resistant wild willows instigated a quest for an alternative hypothesis. This study presents data from laboratory and field experiments that were designed to detect variability in host preferences of individual members of the midge population. Field tests showed that the oviposition site choices of females followed the same random-natured pattern as choices of females in laboratory situations. Ovipositing females did not distinguish between willow genotypes with very high or very low larval mortality. No differences in post-alighting behavior of midges on the two willow types were discovered. Observations revealed that females usually remained and oviposited on the first plant with which they came into contact, regardless of genotype.     

Effects of cotton cultivars differing in gossypol content on the quality of Aphis gossypii as prey for two species of Coccinellidae

Plants can have detrimental effects on biological control agents by affecting their prey or host quality. Thus, it is important to understand the tri-trophic interactions between plants, herbivores and natural enemies when implementing biological control programmes. Studies have shown that both morphological and chemical traits of host plants can affect the third trophic level. Cotton plants are known to produce alkaloids such as gossypol, a sesquiterpene aldehyde that can confer resistance against herbivorous arthropods. Nevertheless, little is known about the effect of gossypol on biological control agents. In this study, we investigated how three cotton cultivars (BRS Rubi, BRS Safira and BRS Verde) differing in gossypol content affect development and growth of predatory coccinellids, Eriopis connexa and Harmonia axyridis, feeding on the cotton aphid Aphis gossypii reared on those cultivars. The results show that the cultivar BRS Rubi (highest gossypol content) had a sub-lethal effect on the development and growth of both Coccinellidae species compared with the other cultivars. Overall, the cultivar BRS Rubi reduced slightly fecundity, net reproductive rate and intrinsic rate of natural increase for both Coccinellidae species. However, because aphid populations stay short periods of time in the field, and adult coccinellids may supplement its diet with alternative prey and plant material this sub-lethal indirect effect of gossypol may not have a detrimental effect on field biological control of cotton aphid by either E. connexa or H. axyridis, thus suggesting a compatibility between plant resistance and biological control agents.     

The biology of Dasineura dielsi Rübsaamen (Diptera: Cecidomyiidae) in relation to the biological control of Acacia cyclops (Mimosaceae) in South Africa

Abstract  Acacia cyclops is an invasive Australian tree in South Africa and a target for biological control using seed-reducing agents. In southern Australia, two gall-forming Cecidomyiidae, Dasineura dielsi (Small Fluted Galler) and Asphondylia sp., develop on the flowers and seeds of A. cyclops , respectively. The larvae of D. dielsi form woody fluted galls on the ovaries of flowers and prevent the development of fruit. Immature Asphondylia sp. develop in the loculi of green fruit and destroy developing seeds. Dasineura dielsi was selected as a biological control candidate for A. cyclops in South Africa and was approved for official release after host specificity evaluation and consideration of potential conflicts of interest. Dasineura dielsi naturalised in South Africa in 2001 and after 3 years dispersed up to 450 km from a single population at Stellenbosch, Western Cape. At sites where D. dielsi has been present longest, high gall densities occur on A. cyclops during the peak flower season in summer. Four hymenopterans, ? Synopeas sp., Mesopolobus sp., Torymus sp. and an unidentified Platygastridae, were reared from D. dielsi galls and are suspected parasitoids of the cecidomyiid, with incidence levels less than 10%. Monitoring is required to evaluate trends in the population status of D. dielsi , its parasitoids and seed production of A. cyclops . Importantly, field monitoring should determine the extent and nature of possible competitive interactions between D. dielsi and an introduced seed-feeding weevil, Melanterius servulus .     

Microsatellite isolation from the gall midge Spurgia capitigena (Diptera: Cecidomyiidae), a biological control agent of leafy spurge

Spurgia capitigena is a gall midge that has been released as a biological control agent of leafy spurge (Euphorbia esula), a noxious rangeland weed in North America. We isolated 15 microsatellite loci from S. capitigena with from two to 27 alleles at each locus. These markers will allow us to examine the structure and levels of neutral genetic variation in native and introduced populations.     

Plant feeding site selection on soybean by the facultatively phytophagous predator Orius insidiosus

Experiments were conducted to test whether the facultatively phytophagous predator Orius insidiosus (Say) (Heteroptera: Anthocoridae) ingested phloem, xylem or mesophyll contents from soybean plants (Glycine max L.). Potential uptake of phloem sap was examined by radiolabeling photosynthate with ¹⁴CO₂ and then measuring the accumulation of radiolabeled metabolites in feeding animals. Most O. insidiosus feeding on radiolabeled plants ingested no or very low levels of label; only 3% ingested small amounts of label, indicating the experimental insects fed very little, if at all, on the phloem. In contrast, well known phloem feeding insects used as positive controls accumulated substantial levels of labeled metabolites after feeding on known host plants. O. insidiosus did feed on xylem contents, as shown by ingestion of safranin-labeled xylem fluid. A few of the insects showed signs of feeding on the mesophyll, as indicated by the presence of chloroplasts in the gut. However, the small diameter of the food canal may cause limited passage of chloroplasts, which would contribute to an underestimation of the frequency of mesophyll feeding. Some radiolabeled metabolites remain in the mesophyll so those insects that ingested low levels of radiolabel probably ingested label from the mesophyll, which supports the notion that some level of mesophyll feeding occurred. Feeding site determines the nutrients ingested during phytophagy. These insects obtain water from the xylem, and may ingest small amounts of starches, sugars, and amino acids from the mesophyll. The results suggest that facultative phytophagy by this heteropteran predator primarily provides the insect with water, but also may provide some nutrients that supplement a prey diet and help the predator survive periods when prey are scarce.     

北方温室内金盏菊对东亚小花蝽定殖及防控草莓害虫的增效作用

田间应用功能植物的保护型生物防治技术,有助于实现天敌昆虫释放后对种群定殖与可持续控害的增效作用,是农业可持续发展的研究热点。为了探究北方冬季温室内功能植物协同捕食性天敌对害虫的控制作用,本研究以蜜源植物金盏菊Calendula offinalis和捕食性天敌东亚小花蝽Orius sauteri为对象,以不含金盏菊为对照,系统研究了金盏菊对东亚小花蝽成虫寿命和定殖的影响,以及对草莓上重要害虫蚜虫和叶螨的防控效果。结果发现,温室种植金盏菊显著增加了东亚小花蝽雌成虫的存活率和寿命,东亚小花蝽雌成虫的寿命达到9.49 d,较对照（6.18 d）延长了53.6%。金盏菊存在显著增加了释放东亚小花蝽后的第2~4周的种群数量,显著降低了草莓植株上棉蚜和叶螨的密度,表明金盏菊通过支持东亚小花蝽存活与种群定殖,增效草莓害虫防控。本研究不仅支持了蜜源植物增效天敌和控制害虫的生态作用,还为北方冬季温室草莓的害虫生物防治方式多元化应用与推广提供实践指导。