Identification of compounds from the eggs of Ostrinia nubilalis and Mamestra brassicae having kairomone activity on Trichogramma brassicae

In the presence of an extract of Ostrinia nubilalis or Mamestra brassicae eggs, female Trichogramma brassicae exhibited increased rates of upwind locomotion in the tubes of a linear olfactometer. GC and GC-MS analyses of O. nubilalis and M. brassicae egg extracts revealed the presence of fatty acids, their ethyl esters, and various hydrocarbons. Exposing the wasps to a mixture of the five main saturated hydrocarbons (heneicosane, tricosane, pentacosane, heptacosane and nonacosane) increased the upwind progression in the olfactometer. Single hydrocarbons elicited reduced or no activity. Ethyl palmitate and palmitic acid were also effective in increasing upwind locomotion. Z11-14:Ac, the main component of the female sex pheromone of O. nubilalis was inactive, regardless of its concentration. It is concluded that various compounds present on the surface of the O. nubilalis egg masses may play a role in the orientation of T. brassicae to its host.     

Flight initiation in the egg parasitoid Trichogramma minutum: Effects of ambient temperature, mates, food, and host eggs

Emergence, preening, and flight initiation were studied in laboratory-reared Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae). Male parasitoids emerged first and flew before females. When both sexes were present in flight cylinders, female parasitoids flew before males. Flight propensity in males was negatively related to the number of emerging females, while flight propensity in females was independent of the number of males present. Ambient temperature significantly affected the propensity and timing of flight; between 70–80% of the parasitoids flew at 25 and 30 °C while less than 4%, mostly males, flew at 20 °C. No flights were observed at 15 °C. The presence of fresh host eggs caused a reduction in the proportion of female parasitoids that flew and a delay in the time to flight for the females that did fly. The presence of food increased the flight propensity of female parasitoids, but did not affect the timing of flight. The relationship between flight behaviour and the efficiency of mass-reared Trichogramma is discussed in terms of its importance for inundative release programmes.     

玉米螟赤眼蜂雌蜂繁殖力与年龄的关系

以米蛾卵作为繁育寄主,通过系统解剖不同发育期（0～144 h）玉米螟赤眼蜂的卵巢,探讨了雌蜂抱卵量、繁殖力与其年龄和个体大小之间的关系。结果表明,玉米螟赤眼蜂在羽化初期（0～3 h）,卵巢中只有部分卵处于成熟状态,随着雌蜂年龄的增加,其抱卵量不断增加,至72 h时接近其卵巢容纳量。抱卵量与雌蜂年龄之间的关系可以用以下公式来表示：y =a｛1-exp［-b(x+c)］｝。用后足胫节长度（HTL）来表示雌蜂个体大小时,HTL短于0.150 mm、介于0.150～0.159 mm之间以及长于0.160 mm的个体羽化后24 h的平均抱卵量分别为40.4、50.5和58.2粒,各占其卵巢容纳量的72.8%、79.3%和86.9%,占整个成虫期总产卵量的49.4%、47.9%及51.9%。玉米螟赤眼蜂羽化后24 h内的产卵量接近于羽化后24 h的抱卵量。雌蜂个体大小与抱卵量及总产卵量之间关系密切,抱卵量与总产卵量随着雌蜂个体的增大而不断增加,呈线性正相关。个体大小可以作为评估玉米螟赤眼蜂生殖潜能高低的一个良好的指标。     

Does host determine short‐range flight capacity of trichogrammatids?

Biological traits, such as body size, fecundity and fertility, of egg parasitoids are strongly influenced by host species, and the use of a single‐host species for consecutive generations has been showed to be detrimental for egg parasitoid biology. Besides biological traits, behaviour of egg parasitoids is also an important parameter for implying their performance in the field, but information about the effect of host on the behaviour of egg parasitoids is still scarce. Thus, this work aimed at determining the influence of host species on the short‐range flight capacity of three egg parasitoids Trichogrammatoidea annulata De Santis, Trichogramma atopovirilia Oatman and Platner and Trichogramma bruni Nagajara reared on Anagasta kuehniella (Zeller), Corcyra cephalonica (Stainton) and Sitotroga cerealella (Olivier), for first, 10 and 28 consecutive generations. Trichogrammatids emerged inside a tubular dark flight chamber, under controlled conditions, and short‐range flying response was based on the proportions of adults trapped to the sticky top of the chamber and the ones found on the bottom, which were checked for defective wings. Our data clearly demonstrate that trichogrammatid short‐range flight depends on the fasctidious host species. All three egg parasitoids had their flight capacity significantly reduced when emerged from S. cerealella. The highest flying capacity of T. annulata was registered when reared on C. cephalonica, while for T. atopovirilia was on A. kuehniella and T. bruni on both C. cephalonica and A. kuehniella. Parasitoid flight capacity is affected when reared on the same host over generations; however, it was not possible to define a pattern for any of the trichogrammatids. Our findings are of great relevance for quality control of mass‐reared egg parasitoids because measuring only behavioural traits with use of flight chambers can be more practical and less time‐consuming than assessing biological parameters.     

Walking pattern of Trichogramma nubilale Ertle & Davis (Hymenoptera; Trichogrammatidae) on various surfaces

The leaf surfaces on which mass-reared Trichogramma spp. are released for augmentative biological control may be an important factor effecting the success of these releases. We observed and recorded the walking pattern of Trichogramma nubilale females on leaves of Zea mays, Canna × generalis (Canna lilly), Silphium perfoliatum (cup plant), Abutilon theophrasti (velvetleaf), Schizachyruim scoparium (little bluestem), a smooth and a fuzzy polyester material, and waxed paper. For each surface type, a total of 10 mated, 1–2 days old, naive and fed females were observed and their walking path was traced. Females walked fastest on waxed paper and leaves of S. scoparium and slowest on leaves of A. theophrasti and the fuzzy material. Turning rates were high on Canna × generalis and waxed paper. In general, walking speed was negatively affected by the presence and density of trichomes and possibly the lack of leaf veins. The effect of surface structures, such as trichomes is likely to scale to the body size of the searching parasitoid. Parasitoids can walk over short trichomes, but short directionally pointed trichomes (as on S. scoparium) can guide the search paths in certain directions. The effects of long trichomes may depend on trichome density relative to the parasitoid body length. When trichome density is on the same order of magnitude as 1/L² (Z. mays), wasps will stand between trichomes, and will frequently run into trichomes, which will retard walking speeds and increase turning.     

Effect of host egg viability on reproduction and development of Trichogramma cacoeciae and T. principium (Hymenoptera: Trichogrammatidae)

A combination of a sterile insect technique, resulting in infertile eggs, and of an egg parasitoid, should provide better control of codling moth than either alone. Non-choice laboratory experiments were conducted with infertile and fertile codling moth eggs to evaluate the potential parasitism and reproduction of Trichogramma cacoeciae Marchal and T. principium Sug. et Sor. The tendency of T. cacoeciae females to attack infertile eggs was similar to that for fertile eggs, whereas T. principium showed a greater preference for infertile eggs than fertile eggs. The fertility status of the host did not affect the number of eggs that were parasitized but fewer F₁ progeny emerged from infertile eggs when parasitized than from fertile eggs. When T. cacoeciae and T. principium parasitized infertile host eggs their mean developmental time was prolonged but the viability and quality of parasitoid progeny was not influenced by the fertility status of the host eggs. The study demonstrates the compatibility of use of T. cacoeciae and T. principium in an integrated program employing the sterile insect technique for codling moth management.     

Possible incompatibility between transgenic cottons and parasitoids

Abstract  We investigated the rates of egg and larval parasitism in transgenic and non-transgenic, conventional cottons. Sentinel eggs and larvae of the cotton bollworm, CBW, Helicoverpa armigera Hübner, were released and collected at regular intervals across the cotton growing season, and the relationship between parasitism and different cotton cultivars determined. Egg and larval parasitism were significantly lower in the transgenic cottons than in the non-transgenic conventional cottons. The egg parasitoid recovered was Trichogramma confusum Viggiani and the predominant larval parasitoids were Campoletis chlorideae Uchida and Meteorus pulchriconis (Wesmael). Our studies indicate a potential negative interaction between transgenic cottons and parasitoids of CBW but need to be interpreted with caution because no within-year replication was used and treatments were not spatially randomised across years.