The ichneumonid Diadromus collaris (Gravenhorst) (Hymenoptera: Ichneumonidae) is a major solitary, pupal endoparasitoid of the diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae). Experiments to examine parasitism of the host pupae of different ages by the parasitoid were conducted in the laboratory. Diadromus collaris preferred host pupae that were in the first half of their pupal development. Survival from larva to adult, and size and parasitizing capacity of the resultant female adults decreased dramatically as host pupal age increased. When ovipositions were made into host pupae that were in the last quarter of their development, all parasitoids died before adult emergence. The performance of D. collaris, as affected by host pupal age, agrees with the simple diet theory that predicts female wasps should select hosts of higher nutritional quality for oviposition.

Hellén [Hymenoptera: Ichneumonidae], Apanteles ippeus Nixon [Hymenoptera: Braconidae], and Oomyzus sokolowskii Kurdjumov [Hymenoptera: Eulophidae]) and one species of pupal parasitoid Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae) attacked immature P. xylostella. The most abundant groups of predatory arthropods caught in pitfall traps were Araneae (Lycosidae)＞Coleoptera (Carabidae, Coccinelidae, Staphylinidae)＞Neuroptera (Chrysopidae)＞Formicidae, whereas on crop foliage Araneae (Clubionidae, Oxyopidae)＞Coleoptera (Coccinelidae)＞Neuroptera (Chrysopidae) were most common. The abundance and diversity of natural enemies was greatest at sites that adopted IPM, correlating greater P. xylostella mortality at these sites. The efÞcacy of the natural enemy complex to pest mortality under different pest management regimes and appropriate strategies to optimize this important natural resource are discussed.

Elevated jasmonic acid (JA) concentrations in response to herbivory can induce wounded plants to produce defences against herbivores. In laboratory and field experiments we compared the effects of exogenous JA treatment to two closely related cabbage species on the host-searching and oviposition preference of the diamondback moth (DBM), Plutella xylostella. JA-treated Chinese cabbage (Brassica campestris) was less attractive than untreated Chinese cabbage to ovipositing DBM, while JA-treatment of common cabbage (B. oleracea) made plants more attractive than untreated controls for oviposition by this insect. Similar effects were observed when plants of the two species were damaged by DBM larvae. In the absence of insect-feeding, or JA application, Chinese cabbage is much more attractive to DBM than common cabbage. Inducible resistance therefore appears to occur in a more susceptible plant and induced susceptibility appears to occur in a more resistant plant, suggesting a possible balance mechanism between constitutive and inducible defences to a specialist herbivore.

Foraging adults of phytophagous insects are attracted by host-plant volatiles and supposedly repelled by volatiles from non-host plants. In behavioural control of pest insects, chemicals derived from non-host plants applied to crops are expected to repel searching adults and thereby reduce egg laying. How experience by searching adults of non-host volatiles affects their subsequent searching and oviposition behaviour has been rarely tested. In laboratory experiments, we examined the effect of experience of a nonhost-plant extract on the oviposition behaviour of the diamondback moth (DBM), Plutella xylostella, a specialist herbivore of cruciferous plants. Naive ovipositing DBM females were repelled by an extract of dried leaves of Chrysanthemum morifolium, a nonhost plant of DBM, but experienced females were not repelled. Instead they were attracted by host plants treated with the non-host-plant extract and laid a higher proportion of eggs on treated than on untreated host plants. Such behavioural changes induced by experience could lead to host-plant range expansion in phytophagous insects and play an important role in determining outcome for pest management of some behavioural manipulation methods.

Laboratory selection was conducted for fenvalerate resistance in two colonies of the parasitoid, Cotesia plutellae Kurdjumov, each reared on a different colony of its host, Plutella xylostella (L.), with different level of resistance to the insecticide. In the selection regime the insecticide was applied to the host larvae that harbored the parasitoid larvae. Compared with the unselected parasitoid colony, the parasitoid colony selected with the susceptible hosts acquired 4.5-fold resistance after 14 selection cycles, while the colony selected with the more resistant hosts acquired 13.6-fold resistance after 13 selection cycles. These results demonstrate that parasitoid larvae could be exposed to insecticide selection via the hosts, selection with more resistant hosts could accelerate development of resistance in the parasitoid, and resistance genes selected during larval development could be expressed at the adult stage. This information can help improve selection procedures for insecticide resistance in parasitoids.

Survival and development time from egg to adult emergence of the diamondback moth, Plutella xylostella (L.), were determined at 19 constant and 14 alternating temperature regimes from 4 to 40℃. Plutella xylostella developed successfully from egg to adult emergence at constant temperatures from 8 to 32℃. At temperatures from 4 to 6℃ or from 34 to 40℃, partial or complete development of individual stages or instars was possible, with third and fourth instars having the widest temperature limits. The insect developed successfully from egg to adult emergence under alternating regimes including temperatures as low as 4℃ or as high as 38℃. The degree-day model, the logistic equation, and the Wang model were used to describe the relationships between temperature and development rate at both constant and alternating temperatures. The degree-day model described the relationships well from 10 to 30℃. The logistic equation and the Wang model fit the data well at temperatures 32℃, but only the Wang model described the decline in development rate at temperatures 32℃. Under alternating regimes, all three models gave good simulations of development in the mid-temperature range, but only the logistic equation gave close simulations in the low temperature range, and none gave close or consistent simulations in the high temperature range. The distribution of development time was described satisfactorily by a Weibull function. These rate and time distribution functions provide tools for simulating population development of P. xylostella over a wide range of temperature conditions.

The development period from birth to adult of alate and apterous virginoparae of the green peach aphid, Myzus persicae (Sulzer), reared on Brassica campestris ssp. chinensis, was measured at 13 constant and five natural temperature regimes. The day-degree model, the logistic equation, and the Wang model were used to describe the relationships between temperature and development rate at constant conditions. The constant temperature-development curves derived from the three models were used with a Weibull function describing the distribution of development times, to simulate the development of individuals of cohorts reared at natural temperature regimes. Comparison of the observed with simulated distributions of adult emergence indicates that all three models can simulate the development of M. persicae very well when the temperature does not go below 4℃, the notional low temperature threshold of the day-degree model. When accumulation of temperatures below 4℃becomes substantial, only the logistic curve with a low temperature threshold of 0℃ can offer accurate simulations; the other two models give falsely longer durations of development. Methods for accurately simulating the development of M. persicae in the field are suggested. The significance of modelling insect development at low temperatures by nonlinear models is discussed.

Laboratory experiments were conducted to examine host selection by Cotesia plutellae Kurdjumov when larvae of its host, Plutella xylostella (Linnaeus), fed on Chinese cabbage, Brassica campestris L. ssp. pekinensis and those fed on common cabbage, Brassica oleracea L. var. capitata were provided simultaneously, and to investigate the roles of plant and host volatiles in mediating host selection. When C. plutellae were provided with equal numbers of host larvae on plants of the two species in one arena, the parasitoid parasitized 4- to 15-fold more host larvae on Chinese cabbage than on common cabbage. This preference changed little with host density. However, an experience of searching coupled with an oviposition in a host larva on a leaf of the less-preferred plant, common cabbage, significantly increased the preference for parasitizing host larvae on this plant and resulted in twice as many host larvae parasitized on this plant than on Chinese cabbage. Dual choice tests with a Y-tube olfactometer showed that plant volatiles from Chinese cabbage were more attractive to female C. plutellae than those from common cabbage when plants of both species were either intact or infested. In parallel to the increased parasitism on common cabbage following experience, oviposition in a host larva on this less-preferred plant significantly increased the response to volatiles emanating from that plant. These results indicate that host plants may strongly influence the foraging behaviour of C. plutellae, but their differential attractiveness to the parasitoid may be altered by experience of the parasitoid.

Diadromus collaris (Gravenhorst) (Hymenoptera: Ichneumonidae) has been recorded in many parts of the world as a major pupal endoparasitoid of the diamondback moth Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae). Experiments were conducted to compare reproductive compatibility and performance as affected by temperature between two geographic populations of D. collaris, one from Hangzhou, Zhejiang and the other from Lishan, Taiwan, China. The numbers and sex ratio of progeny in all possible crosses and backcrosses were similar to those obtained within each of the populations, demonstrating complete reproductive compatibility between the two populations. The two populations showed similar responses to temperature with respect to development time, adult longevity and number of host pupae parasitized per female. However, the population from Hangzhou achieved higher rates of survival from larva to adult emergence at high temperatures and had higher proportions of female progeny at some temperatures, than the population from Lishan. The Hangzhou population achieved higher intrinsic rates of increase at all temperatures tested from 15 to 33.5℃, and the differences were significant at 30 and 32℃. The differences between the two populations in ability to survive high temperatures may reflect their adaptation to local climates. The significance of the intraspecific variations revealed is discussed with regard to the use of geographic populations of the parasitoid in the biological control of P. xylostella.

The term 'dead-end trap cropping' has recently been proposed to identify a plant that is highly attractive for oviposition by an insect pest, but on which offspring of the pest cannot survive. The potential of the wild crucifer Barbarea vulgaris R. Br. to allure and serve as a dead-end trap crop for the diamondback moth Plutella xylostella (L.), an important pest of cruciferous crops worldwide, was examined in laboratory experiments. When P. xylostella adults were provided with a dual-choice of plants of B. vulgaris, and Chinese cabbage Brassica campestris (L.), in one arena, adult moths laid 2.5-6.8 times more eggs on the former than on the latter. When P. xylostella adults were provided with a dual-choice of plants of B. vulgaris and common cabbage Brassica oleracea L., adult moths laid virtually all their eggs on the former and ignored the latter. Nearly all P. xylostella eggs laid on the three species of plants hatched successfully, but nearly all individuals on plants of B. vulgaris died as neonates or early instar larvae, while 87-100% of the larvae on Chinese cabbage and common cabbage survived to pupation. Dual choice tests with a Y-tube olfactometer showed that volatiles from B. vulgaris were much more attractive to P. xylostella adults than those from common cabbage. The results demonstrate that B. vulgaris has a great potential as a dead-end trap crop for improving management of P. xylostella. Factors that may influence the feasibility of using B. vulgaris as a trap crop in the field are discussed, and ways to utilize this plant are proposed.