Using hosts of mixed sizes to reduce male-biased sex ratio in the parasitoid wasp, Diglyphus isaea

Overproduction of males in mass rearing of parasitic Hymenoptera contributes to higher costs for biological control because only females directly kill pests. We present a technique, based on manipulating host composition, to generate less male‐biased sex ratios in parasitoid species that adjust their sex allocation in response to relative host size. Our system consisted of chrysanthemum, Dendranthema grandiflora Tzvelev var. ‘Miramar’; a leafminer, Liriomyza langei Frick (Diptera: Agromyzidae); and a commercially available parasitoid, Diglyphus isaea (Walker) (Hymenoptera: Eulophidae). We compared the offspring sex ratios of D. isaea females presented with different compositions of L. langei larvae on chrysanthemum. Presenting individual females with only large hosts increased mean sex ratio from 32 to 67% male over 2 days. However, presenting individual females with progressively larger hosts over 1 or 2 days reduced mean sex ratio from 90 to 100% male to less than 30% male. Groups of females produced sex ratios around 58% male if presented with both plants infested by only small hosts and plants infested by only large hosts. In comparison, groups of females produced sex ratios around 48% male if presented with plants infested by both small hosts and large hosts. We compared the use of both small hosts and large hosts to only large hosts for simulated mass rearing of wasps over 8 weeks. Using both small hosts and large hosts produced similar numbers of wasps as using only large hosts, but reduced mean sex ratio of weekly cohorts from 66% male to 56% male. The two techniques produced females of similar size, but using both large hosts and small hosts produced slightly smaller males than using only large hosts. The use of both small hosts and large hosts for mass rearing of D. isaea could reduce actual costs of females by 23%.     

Leaf puncturing, feeding and oviposition behavior of Liriomyza trifolii

The leaf puncturing, ovipositional and feeding behavior of Liriomyza trifolii was investigated on a preferred and non-preferred host (chrysanthemum and tomato, respectively). The sequence of leaf-puncturing behavior was stereotypic on both hosts, with a high probability of transition from one event to the next once the sequence is initiated. Two types of leaf punctures were made: a large fan-shaped puncture without an egg and tubular-shaped punctures with or without an egg. Regardless of the type of leaf puncture created, the female always backed over the puncture to feed. Therefore, all leaf punctures can be considered as feeding punctures. Fewer slow abdominal thrusts were noted for flies during oviposition compared to leaf puncturing only on chrysanthemum and tomato. The major differences noted between hosts were that L. trifolii fed for a significantly shorter period and spent less time during the leaf puncturing sequence on tomato vs. chrysanthemum. This suggests a repellent/antifeedant present in the former host which is detected through gustatory mechanisms. The deposition of an epideictic pheromone during oviposition was not detected.

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Résumé L'étude des comportements de piqûre, de ponte et d'alimentation de Liriomyza trifolii a été réalisée sur hôtes préférés ou non (Chrysanthème ou tomate). Les séquences du comportement de piqûre de feuilles sont stéréotypées sur les deux plantes, avec une forte probabilité de transmission d'une séquence à la suivante quand le comportement a débuté.II y avait deux types de piqûres de feuilles: de larges piqûres coniques sans oeufs et des piqûres tubulaires avec ou sans oeuf. Sans considération du type de piqûre, la femelle retourne sur la piqûre pour s'alimenter. Ainsi, toutes les piqûres peuvent être considérées comme des piqûres alimentaires. Moins de lentes contractions abdominales ont été observées chez les mouches pondant que chez celles piquant uniquement, tant sur chrysanthème que tomate. Les principales différences observées entre hôtes ont été que L. trifolii s'alimentait pendant moins longtemps et passait moins de temps pendant la perforation sur tomate que sur chrysanthème. Ceci suggère la présence d'un répulsif/dissuadant chez la tomate qui serait décelé par la gustation. Aucun dépôt de phéronome épidéictique n'a été mis en évidence pendant la ponte.

     

Genetic differentiation and speciation in leaf-mining flies of the genus Phytomyza

Population structure is one of the most important factors determining speciation potential. We analyzed the spatial variation in allozyme frequencies of Phytomyza chaerophylli Kalt. (Diptera: Agromyzidae) using Wright's F-statistics. The degree of interpopulation variation is substantial (F_ST=0.092). Variation between local populations separated by only a few kilometers is as high as between populations as far as 1000 kilometers apart, indicating low interpopulation gene flow. The results are supported by ecological studies which revealed that host plant populations of P. chaerophylli, as well as of other, closely related Phytomyza species, are patchily distributed and have a short average life span. Populations of many Phytomyza species are thus mostly small and partly isolated and are prone to frequent extinctions and bottlenecks. Such conditions greatly increase the chance of rare mutations being fixed in new populations which may eventually lead to speciation. It is argued that the ecology and population structure of P. chaerophylli and congeners favor rapid speciation.

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Zusammenfassung Die Populationsstruktur ist einer der wichtigsten Faktoren, die das Speziationspotential einer Species bestimmen. Wir analysierten die räumliche Variation der Allozymfrequenzen von Phytomyza chaerophylli Kalt. (Diptera: Agromyzidae) nach den Methoden von Wrights F-Statistik. Der Grad der genetischen Variation zwischen den Populationen ist beträchtlich (F_ST=0.092). Die Variation zwischen lokalen, lediglich durch wenige Kilometer voneinander getrennten Populationen ist gleich gross wie zwischen Populationen, die bis zu 1000 Kilometer auseinander liegen. Eine solche Differenzierung deutet auf einen niedrigen Genfluss zwischen den Populationen. Die Ergebnisse der genetischen Analyse werden gestützt durch ökologische Studien, welche zeigten, dass Wirtspflanzenpopulationen von P. chaerophylli und anderen, nah verwandten Phytomyza-Arten eine inselartige Verbreitung aufweisen und eine verhältnismässig kurze mittlere Lebensdauer haben. Die Populationen von vielen Phytomyza-Arten sind daher meist klein und teilweise isoliert und unterliegen häufig Ausrottungen und genetischen Flaschenhälsen (Bottlenecks). Solche Bedingungen vergrössern beträchtlich die Chance, seltene Mutationen in neuen Populationen zu fixieren, was unter Umständen zu Speziation führen kann. Wir stellen fest, dass Ökologie und Populationsstruktur von P. chaerophylli und anderen Arten dieses Genus günstige Voraussetzungen für eine schnelle Speziation darstellen.

     

Role of volatile infochemicals in foraging behavior of the leafminer parasitoidDacnusa sibirica (Diptera: Agromyzidae)

Previous investigations suggested that the leafminer parasitoid Dacnusa sibirica Telenga does not use a volatile hostrelated infochemical in foraging for hosts. Parasitoids landed with equal frequencies on an uninfested tomato plant and on a tomato plant infested with larvae of the leafminer Liriomyza bryoniae (Kalt.) (Hendrikse et al., 1980). In contrast, we found that volatile infochemicals emitted by uninfested and leafminer-infested tomato plants differently affected the parasitoid 's foraging behavior in a windtunnel. This was obvious from the proportion of wasps flying upwind but not from the proportion of wasps landing on the leaves. Latency time on an uninfested tomato leaflet and proportion of latency time devoted to preflight antennal behavior were influenced by the presence of upwind infested or uninfested tomato leaves. However, these parameters were not affected by odors in the absence of visual plant stimuli. Our data provide a new view on foraging behavior of Dacnusa sibirica.     

中国萝潜蝇属分类研究 (双翅目: 潜蝇科)

研究了中国萝潜蝇属Napomyza Westwood,确认该属在我国现知下列6种：环萝潜蝇Napomyza annulipes (Meigen),角萝潜蝇N.hirticornis(Hendel),菊茎萝潜蝇N.lateralis (Fallen),拟土萝潜蝇N.paratripolii sp. Nov.,毛萝潜蝇N. plumea Spencer和西藏萝潜蝇N. xizangensis sp. Nov.。除描述二新种并附特征图外, 还提供中国已知种类的鉴别特征和分种检索表。     

中国热潜蝇属一新种(双翅目,潜蝇科)

记述了热潜蝇属Tropicomyia Spencer1新种：云南热潜蝇T．yunnanensis sp．nov,附形态特征图,并提供该属中国现知6种的分种检索表。模式标本存放于中国科学院动物研究所。     

Evolution of host avoidance in a leafmining fly, Amauromyza flavifrons

Herbivorous insects are characterized by a great diversity of host plant associations, yet, the processes driving host range evolution are not fully understood. When herbivores encounter a novel host, local selection pressures are expected to shape traits that mediate plant–insect interactions. I show that a leafmining fly, Amauromyza flavifrons (Meigen) (Diptera: Agromyzidae), suffers a profound fitness cost by ovipositing on a novel host, Beta vulgaris L. (sugar beet) (Chenopodiaceae). Leafminers from a sugar beet-free population readily oviposit on B. vulgaris leaves, whereas those collected from a population near sugar beet farms discriminate against B. vulgaris . This finding suggests that oviposition specificity in A. flavifrons populations may have evolved in response to the presence of the novel host, and represents the first evidence of host-avoidance evolution in the wild. Because this study compared only one pair of populations and thus lacks replication, future studies will test whether parallel evolution has occurred at B. vulgaris farm locales across North America.     

Variation of density-dependence with spatial scale in the leaf-mining fly Liriomyza commelinae (Diptera: Agromyzidae)

Abstract. 1. Mortality imposed on the leaf mining fly, Liriomyza commelinae (Frost) was studied at three spatial levels: (1) the leaf, (2) the stem, and (3) a metre quadrat of the food plant.
2. Real mortality (R.M.) (death as a percentage of eggs laid) during development for five sites over 3 years (forty-seven generations) was 96.3 + 1.9% -2.5% (±95% c.l.), due mainly to parasitoids and predatory ants, with a small component due to competition and other causes.
3. Real mortality due to the parasitoid complex averaged 41.2%. It was not related to population density in leaves or stems but was positively dependent on density in one metre quadrats.
4. Predation by Crematogaster brevispinosa Mayr was 21.2% and was independent of population density at all spatial levels.
5. Mortality due to other causes (e.g. competition and exposure to high temperature resulting from insolation) was positively dependent on the number of mines per leaf at three out of five sites studied and the number of mines per stem at two of the three sites studied; however, such mortality was independent of density per metre quadrat.     

Effect of soil-applied complex fertiliser on an insect–host plant relationship: Liriomyza trifolii on Solanum tuberosum

Insects respond to very low levels of nutritional and non‐nutritional compounds in plants, which influence their acceptance and colonisation of the plant or plant part, and thereby their growth and development. Plant nutrient levels can vary within and between plants, and are influenced by external factors such as fertiliser treatments, irrigation regime, and light. Soil levels of nitrogen, potassium, phosphorus, calcium, and magnesium can have significant effects on the amounts of these nutrients in the plant, and thereby on pest infestation. This study reports on the influence of seven different NPK fertiliser rates in potted potato (Solanum tuberosum cv. Mondial) plants on the nitrogen, phosphorus, potassium, calcium, and magnesium levels in the leaves, and the concomitant influence on infestation by, and development of, the serpentine leafminer, Liriomyza trifolii Burgess (Diptera: Agromyzidae). Results showed that increases in nitrogen in the potato leaves increased larval and pupal survival, and pupal and adult body weight and length. Potassium and phosphorus, on the other hand, decreased the host suitability of potato plants to L. trifolii, and were detrimental to the pest.