Holotrichia parallela damages seriously on peanut (Arachis hypogaea) pods. Elucidation of its flight and walking performance in the presence of different plants may provide an insight in its host selection process and an explanation to its strong olfactory preference to an attractive nonhost, castor bean (Ricinus communis). We determined the relationships among flight performance, mate choice, and body weight of H. parallela beetles, and then investigated their flight and walking patterns in the presence of known hosts and attractive nonhost plants using a flight mill and a locomotion compensator, respectively. Body weights were not related to mating success, regardless of sex. The flight proportion of selected females drastically decreased compared with nonselected females, nonselected males, and selected males. Within mated males, heavier individuals exhibited poorer flight performance than lighter ones. In flight bioassay, peanut showed an arrestment effect on virgin females. For walking activity factors (distance, time, and speed), the host plants velvetleaf (Abutilon theophrasti) and Siberian elm (Ulmus pumila) elicited the strongest responses in females and males, respectively. Interestingly, the most preferred adult host, Siberian elm, and the nonhost, castor bean, elicited the highest values of two orientation factors (orientation and upwind length) in females. The chemical similarity hypothesis, which states that feeding or oviposition of insects mistakenly on nonhost can be traced to their chemical similarity to actual hosts, could explain the attraction of H. parallela to castor bean.

The castor bean, Ricinus communis L., is a non-host plant for the large black chafer, Holotrichia parallela Motschulsky (Coleoptera: Scarabaeidae). In laboratory bioassays we found that this plant was no less attractive than the main host plant (peanut, Arachis hypogaea) and three food plant species: velvetleaf (Abutilon theophrasti), the glossy privet (Ligustrum lucidum), and the Siberian elm (Ulmus pumila). In field trapping experiments a Soxhlet extract of castor bean leaves caught more beetles than the optimal sex lure blend [(R)-(-)-linalool and (L)-isoleucine methyl ester blended in a ratio of 1:4], compared at equal doses (500 μl), and laboratory bioassays indicated that a castor bean plant could enhance the attractiveness of different blend ratios of sex lures. Olfactometer bioassays showed that males prefer volatiles emitted from different combinations of castor bean plant extracts and a signaling female over a female alone. In the presence of castor bean plants copulation rates of H. parallela were highest among all test environments both in laboratory bioassays (60%) and in field tests (70%). This study, combined with our previous observation of the feeding behavior of H. parallela adults on castor bean leaves, suggests that castor bean plants may provide an attractive but risky mating site for H. parallela beetles. The enhancement of male mate-location and copulation rate in the presence of castor bean plants can balance its paralytic effects on H. parallela after intake of potential toxins contained in its leaves.

Experience is well known to affect sensory-guided behaviors in many herbivorous insects. Here, we investigated the effects of natural feeding experiences of Helicoverpa armigera larvae on subsequent preferences of larval approaching and feeding, as well as the effect of host-contacting experiences of mated females on subsequent ovipositional preference. The results show that the extent of experience-induced preference, expressed by statistical analysis, depended on the plant species paired with the experienced host plant. Larval feeding preference was much easier to be induced by natural feeding experience than larval approaching preference. Naïve larvae, reared on artificial diet, exhibited clear host-ranking order as follows: tobacco ≥ cotton > tomato > hot pepper. Feeding experiences on hot pepper and tobacco could always induce positive feeding preference, while those on cotton often induced negative effect, suggesting that the direction of host plant experience-induced preference is not related to innate feeding preference. Inexperienced female adults ranked tobacco as the most preferred ovipositional host plant, and this innate preference could be masked or weakened but could not be reversed by host-contacting experience after emergence.

The tobacco Nicotiana rustica is widely used as a trap crop in the fields of Nicotiana tabacum in China, by attracting oviposition of Helicoverpa assulta females, thus preventing damage to N. tabacum. The mechanism underlying the differential oviposition rates of H. assulta across these two tobacco species, however, is largely unknown. We investigated the mechanism of host plant acceptance of H. assulta with respect to these two tobaccos by using a two-choice behavioral bioassay and GC–MS. Our results indicate that both the leaves and inflorescences of N. rustica attracted significantly more eggs than the corresponding parts of N. tabacum. Extracts of leaves and inflorescences of N. rustica with two different solvents elicited similar oviposition patterns to the corresponding parts of the plants. Chemical analysis by GC–MS revealed that the volatiles of N. rustica contain larger amounts of nicotine than those of N. tabacum at the flowering stage. In addition, γ-terpinolene and β-elemene are found only in extracts of N. rustica. A two-choice bioassay on the individual compounds showed that γ-terpinolene, which is specific to the vegetative stage of N. rustica, and nicotine attracted oviposition by H. assulta. The volatile β-elemene, which is present only in N. rustica, was also attractive. We conclude that the larger amount of nicotine, and the species-specific γ-terpinolene and β-elemene may mediate the different oviposition rates of H. assulta females across N. rustica and N. tabacum.

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